FILED PURSUANT TO RULE
                                                         424(b)(1). REGISTRATION
                                                                   NO. 333-34379
    
 
   
    PROSPECTUS
    
 
                         ATLANTIC PHARMACEUTICALS, INC.
 
                        250,000 SHARES OF COMMON STOCK,
                   OFFERED BY CERTAIN SELLING SECURITYHOLDERS
                            ------------------------
 
    This prospectus (the "Prospectus") relates to the public offering, which is
not being underwritten, of 250,000 shares (the "Shares") of Common Stock, par
value $0.001 per share (the "Common Stock"), of Atlantic Pharmaceuticals, Inc.,
a Delaware corporation ("Atlantic" or the "Company"). All of the Shares may be
offered by certain stockholders of the Company or by pledgees, donees,
transferees or other successors in interest that receive such shares as a gift,
partnership distribution or other non-sale related transfer (the "Selling
Securityholders"). The Shares were received by certain Selling Securityholders
in a private placement transaction of the Company and were issued pursuant to an
exemption from the registration requirements of the Securities Act of 1933, as
amended (the "Securities Act"), provided by Section 4(2) thereof. The Shares are
being registered by the Company pursuant to a registration rights agreement with
certain Selling Securityholders. See "Description of Securities" and "Plan of
Distribution."
 
    The Shares may be offered by the Selling Securityholders from time to time
in transactions on the Nasdaq SmallCap Market ("Nasdaq"), in privately
negotiated transactions, or by a combination of such methods of sale, at fixed
prices that may be changed, at market prices prevailing at the time of sale, at
prices related to such prevailing market prices or at negotiated prices. The
Shares may be sold by one or more of the following: (a) a block trade in which
the broker or dealer so engaged will attempt to sell the Shares as agent but may
position and resell a portion of the block as principal to facilitate the
transaction, (b) purchases by a broker or dealer as principal and resale by such
broker or dealer for its account pursuant to this Prospectus and (c) ordinary
brokerage transactions and transactions in which the broker solicits purchases.
The Selling Securityholders may effect such transactions by selling the Shares
to or through broker-dealers and such broker-dealers may receive compensation in
the form of discounts, concessions or commissions from the Selling
Securityholders or the purchasers of the Shares for whom such broker-dealers may
act as agent or to whom they sell as principal or both (which compensation to a
particular broker-dealer might be in excess of customary commissions). In
addition, any securities covered by this Prospectus which qualify for sale
pursuant to Rule 144 may be sold under Rule 144 promulgated under the Securities
Act rather than pursuant to this Prospectus. The Company will not receive any of
the proceeds from the sale of the Shares by the Selling Securityholders. The
Company has agreed to bear certain expenses in connection with the registration
and sale of the Shares being offered by the Selling Securityholders and to
indemnify the Selling Securityholders against certain liabilities, including
liabilities under the Securities Act. See "Plan of Distribution."
 
   
    The Units, Common Stock and Redeemable Warrants of the Company are traded on
The Nasdaq SmallCap Market tier of The Nasdaq Stock Market under the symbols
"ATLCU," "ATLC" and "ATLCW," respectively. On November 11, 1997, the last sale
price for the Units, Common Stock and Redeemable Warrants as quoted on Nasdaq
was $13.00, $9.0625 and $4.375, respectively, per security.
    
                            ------------------------
 
    The Selling Securityholders and any broker-dealers or agents that
participate with the Selling Securityholders in the distribution of the Shares
may be deemed to be "underwriters" within the meaning of Section 2(11) of the
Securities Act, and any commissions received by them and any profit on the
resale of the Shares purchased by them may be deemed to be underwriting
commissions or discounts under the Securities Act.
                            ------------------------
 
    THE SECURITIES OFFERED HEREBY INVOLVE A HIGH DEGREE OF RISK. SEE "RISK
FACTORS" BEGINNING ON PAGE 3.
                             ---------------------

 THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
     EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION
         PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY
            REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
 
                            ------------------------
 
   
               THE DATE OF THIS PROSPECTUS IS NOVEMBER 12, 1997.
    
                            ------------------------

    No dealer, salesperson or other person has been authorized to give any
information or to make any representations other than those contained in this
Prospectus and, if given or made, such information or representations must not
be relied upon as having been authorized by the Company, any Selling
Securityholders or by any other person. This Prospectus does not constitute an
offer to sell or a solicitation of an offer to buy any securities other than the
shares of Common Stock offered hereby, nor does it constitute an offer to sell
or a solicitation of an offer to buy any of the shares offered hereby to any
person in any jurisdiction in which such offer or solicitation would be
unlawful. Neither the delivery of this Prospectus nor any sale made hereunder
shall under any circumstances create any implication that the information
contained herein is correct as of any date subsequent to the date hereof.
 
                             AVAILABLE INFORMATION
 
    Atlantic was incorporated in the State of Delaware on May 18, 1993 and
commenced operations on July 13, 1993. As used in this Prospectus, unless the
context requires otherwise, the "Company" means Atlantic Pharmaceuticals, Inc.
and its subsidiaries. The Company's principal executive offices are located at
1017 Main Campus Drive, Suite 3900, Raleigh, North Carolina 27606. The Company's
telephone number at that address is (919) 513-7020. The Company's Units, Common
Stock, and Redeemable Warrants are quoted on Nasdaq under the respective symbols
"ATLCU," "ATLC" and "ATLCW."
 
    Atlantic is subject to the information requirements of the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), and in accordance
therewith, is required to file periodic reports, proxy materials and other
information with the Securities and Exchange Commission (the "Commission").
Reports, proxy statements and other information can be inspected and copied at
the public reference facilities maintained by the Commission at Room 1024,
Judiciary Plaza, 450 Fifth Street, N.W., Washington, D.C. 20549, or at its
regional offices located at Suite 1400, Northwest Atrium Center, 500 West
Madison Street, Chicago, Illinois 60661 and at 7 World Trade Center, Suite 1300,
New York, New York 10048. Copies of such materials may also be obtained from the
Public Reference Section of the Commission, 450 Fifth Street, N.W., Washington,
DC 20549, at prescribed rates. In addition, the Commission maintains a World
Wide Web site that contains reports, proxy and information statements and other
information regarding issuers, including the Company, that file electronically
with the Commission. Such Web site can be found at http://www.sec.gov. The
materials described above may also be inspected at the offices of Nasdaq
Operations, 1735 K Street, N.W., Washington, DC 20006.
 
    This Prospectus, which constitutes a part of a Registration Statement on
Form S-3 (the "Registration Statement") filed by the Company with the Commission
under the Securities Act, omits certain of the information set forth in the
Registration Statement and the exhibits and schedules thereto. For further
information with respect to the Company and the Shares offered hereby, reference
is made to the Registration Statement and the exhibits and schedules filed as a
part thereof. Statements contained in this Prospectus concerning the contents of
any contract or any other document referred to are not necessarily complete;
reference is made in each instance to the copy of such contract or document
filed as an exhibit to the Registration Statement. Each such statement is
qualified in all respects by such reference to such exhibit. The Registration
Statement, including all exhibits and schedules thereto, may be inspected
without charge at the Commission's principal office in Washington, D.C., and
copies of all or any part thereof may be obtained from such office after payment
of fees prescribed by the Commission.
 
                     INFORMATION INCORPORATED BY REFERENCE
 
    The following documents filed by the Company with the Commission (File No.
0-19750) pursuant to the Exchange Act are incorporated by reference in this
Prospectus:
 
   
    1.  The Company's Annual Report on Form 10-KSB for the fiscal year ended
       December 31, 1996, Quarterly Report on Form 10-QSB for the fiscal quarter
       ended March 31, 1997, Current Report on Form 8-K filed with the
       Commission on June 9, 1997, Quarterly Report on Form 10-QSB for
    
 
                                       2

   
       the fiscal quarter ended June 30, 1997 and Quarterly Report on Form
       10-QSB for the fiscal quarter ended September 30, 1997;
    
 
    2.  The Company's definitive Proxy Statement dated May 8, 1997 filed in
       connection with the Company's 1997 Annual Meeting of Stockholders;
 
    3.  The description of the Company's securities contained in the Company's
       Registration Statement on Form 8-A filed under the Exchange Act on
       November 27, 1995, including any amendment or report filed for the
       purpose of updating such description.
 
    All documents filed by the Company pursuant to Sections 13(a), 13(c), 14 or
15(d) of the Exchange Act subsequent to the date of this Prospectus but prior to
the termination of the offering to which this Prospectus relates shall be deemed
to be incorporated by reference in this Prospectus and to be part hereof from
the date of filing of such documents. Any statement contained in a document
incorporated by reference herein shall be deemed to be modified or superseded
for purposes of this Prospectus to the extent that a statement contained herein
or in any other subsequently filed document which also is incorporated herein
modifies or supersedes such statement. Any statement so modified or superseded
shall not be deemed, in its unmodified form, to constitute a part of this
Prospectus.
 
    Upon written or oral request, the Company will provide without charge to
each person to whom a copy of the Prospectus is delivered a copy of the
documents incorporated by reference herein (other than exhibits to such
documents unless such exhibits are specifically incorporated by reference
therein). Requests should be submitted in writing or by telephone at (919)
513-7020 to Director of Investor Relations, Atlantic Pharmaceuticals, Inc., at
the principal executive offices of the Company, 1017 Main Campus Drive, Suite
3900, Raleigh, North Carolina 27606.
 
                                       3

                                  RISK FACTORS
 
    AN INVESTMENT IN THE SECURITIES OFFERED HEREBY IS SPECULATIVE IN NATURE,
INVOLVES A HIGH DEGREE OF RISK AND SHOULD NOT BE MADE BY AN INVESTOR WHO CANNOT
AFFORD THE LOSS OF HIS ENTIRE INVESTMENT. THE FOLLOWING RISK FACTORS SHOULD BE
CONSIDERED CAREFULLY IN ADDITION TO THE OTHER INFORMATION CONTAINED OR
INCORPORATED BY REFERENCE IN THIS PROSPECTUS BEFORE PURCHASING THE SECURITIES
OFFERED HEREBY. IN ADDITION TO THE HISTORICAL INFORMATION CONTAINED HEREIN, THE
DISCUSSION IN THIS PROSPECTUS CONTAINS CERTAIN FORWARD-LOOKING STATEMENTS,
WITHIN THE MEANING OF SECTION 27A OF THE SECURITIES ACT AND SECTION 27E OF THE
EXCHANGE ACT, THAT INVOLVE RISKS AND UNCERTAINTIES, SUCH AS STATEMENTS OF THE
COMPANY'S PLANS, OBJECTIVES, EXPECTATIONS AND INTENTIONS. THE CAUTIONARY
STATEMENTS MADE IN THIS PROSPECTUS SHOULD BE READ AS BEING APPLICABLE TO ALL
RELATED FORWARD-LOOKING STATEMENTS WHEREVER THEY APPEAR IN THIS PROSPECTUS. THE
COMPANY'S ACTUAL RESULTS COULD DIFFER MATERIALLY FROM THOSE DISCUSSED HEREIN.
FACTORS THAT COULD CAUSE OR CONTRIBUTE TO SUCH DIFFERENCES INCLUDE THOSE
DISCUSSED BELOW AS WELL AS THOSE CAUTIONARY STATEMENTS AND OTHER FACTORS SET
FORTH ELSEWHERE HEREIN.
 
DEVELOPMENT STAGE COMPANIES; HISTORY OF OPERATING LOSSES; ACCUMULATED DEFICIT;
  UNCERTAINTY OF FUTURE PROFITABILITY
 
    The technologies and products under development by the Company are in the
research and development stage and no operating revenue, outside of grant
revenues, have been generated to date. The Company does not expect to generate
any revenues in the near future. As a result, the Company must be evaluated in
light of the problems, delays, uncertainties and complications encountered in
connection with newly established businesses. The Company has incurred operating
losses since its inception. As of June 30, 1997, the Company's working capital
and accumulated deficit were $1,988,899 and $11,276,353, respectively. Operating
losses have resulted principally from costs incurred in identifying and
acquiring the technologies under development, research and development
activities and from general and administrative costs. The Company expects to
incur significant operating losses over the next several years, primarily due to
continuation and expansion of its research and development programs, including
preclinical studies and clinical trials for its pharmaceutical products under
development. The Company's ability to achieve profitability depends upon its
ability to develop pharmaceutical and medical device products, obtain regulatory
approval for its proposed products and enter into agreements for product
development, manufacturing and commercialization. There can be no assurance that
the Company will ever achieve significant revenues or profitable operations from
the sale of its proposed products.
 
AUDITOR'S OPINION
 
    The Company's independent accountants have included an explanatory paragraph
in their report on the Company's financial statements at December 31, 1996,
included in the Company's 1996 Annual Report on Form 10-KSB, which states that
the Company has suffered recurring losses from operations and has limited
capital resources, both of which raise substantial doubt about the Company's
ability to continue as a going concern.
 
NEED FOR ADDITIONAL FINANCING; ISSUANCE OF SECURITIES BY THE COMPANY AND ITS
  SUBSIDIARIES; FUTURE DILUTION
 
    The Company will require, and is constantly considering potential sources
for, substantial additional financing to continue its research, to complete its
product development and to manufacture and market any products that may be
developed. Based solely upon its currently existing consulting, license,
sponsored research and employment agreements, the Company currently anticipates
that it will spend all of its current cash reserves by late 1999. There can be
no assurance, however, that the Company's current cash reserves will not be
expended prior to that time. The Company anticipates that further funds may be
raised at any time through additional public or private debt or equity
financings conducted either by the Company or by one or more of its
subsidiaries, or through collaborative ventures entered into between the Company
or one or more of its subsidiaries and a corporate partner. There can be no
assurance that the
 
                                       4

Company will be able to obtain additional financing or that such financing, if
available, can be obtained on terms acceptable to the Company. If additional
financing is not otherwise available, the Company will be required to modify its
business development plans or reduce or cease certain or all of its operations.
In such event, holders of securities of the Company will, in all likelihood,
lose their entire investment.
 
    Although the Company and each of its subsidiaries will seek to enter into
collaborative ventures with corporate sponsors to fund some or all of such
activities, as well as to manufacture or market the products which may be
successfully developed, neither the Company nor any of its subsidiaries
currently has any such arrangements with corporate sponsors, and there can be no
assurance that the Company or any of its subsidiaries will be able to enter into
such ventures on favorable terms, if at all. In addition, no assurance can be
given that the Company or any of its subsidiaries will be able to complete a
subsequent private placement or public offering of their securities. Failure by
the Company or any of its subsidiaries to enter into such collaborative ventures
or to receive additional funding to complete its proposed product development
programs either through a public offering or a private placement would have a
material adverse effect on the Company.
 
    In the event that the Company obtains any additional funding, such
financings may have a dilutive effect on the holders of the Company's
securities. In addition, if one or more of the Company's subsidiaries raises
additional funds through the issuance and sale of its equity securities, the
interest of the Company and its stockholders in such subsidiary or subsidiaries,
as the case may be, could be diluted and there can be no assurance that the
Company will be able to maintain its majority interest in any or all of its
current subsidiaries. In addition, the interest of the Company and its
stockholders in each subsidiary will be diluted or subject to dilution to the
extent any such subsidiary issues shares or options to purchase shares of its
capital stock to employees, directors, consultants and others. In the event that
the Company's voting interest in any of its current subsidiaries falls below
50%, the Company may not be able to exercise an adequate degree of control over
the affairs and policies of such subsidiary as currently being exercised. In
addition, the Company has outstanding currently exercisable Redeemable Warrants
and options to purchase 3,826,750 and 699,155 shares of its Common Stock,
respectively, at exercise prices ranging from $5.50 to $10.00, and $0.75 to
$7.50, respectively, and the exercise price for most of such Redeemable Warrants
and options is below the per share price of the Common Stock as currently quoted
on Nasdaq. The Company also has outstanding 1,237,200 shares of its Series A
Preferred Stock and warrants to purchase 123,720 shares of Series A Preferred
Stock, all of which are convertible into shares of the Company's Common Stock.
The exercise of such warrants and options or the conversion of the Series A
Preferred Stock, if any, may dilute the value of the Common Stock.
 
NO DEVELOPED OR APPROVED PRODUCTS
 
    To achieve profitable operations, the Company, alone or with others, must
successfully develop, obtain regulatory approval for, introduce and market its
products under development. The great majority of the preclinical and clinical
development work for the products under development of the Company remains to be
completed. The Company has not generated, nor is it expected to generate in the
near future, any operating revenues. In addition, the Company has no
manufacturing or marketing facilities nor any contracts with any commercial
manufacturing or marketing entities. No assurance can be given that any of its
product development efforts will be successfully completed, that required
regulatory approvals will be obtained, or that any such products, if developed
and introduced, will be successfully marketed or achieve market acceptance.
 
TECHNOLOGICAL UNCERTAINTY AND EARLY STAGE OF PRODUCT DEVELOPMENT
 
    The technologies and products which the Company intends to develop are in
the early stages of development, require significant further research,
development and testing and are subject to the risks of failure inherent in the
development of products based on innovative or novel technologies. These risks
include the possibility that any or all of the Company's proposed technologies
and products will be found
 
                                       5

to be ineffective or unsafe, that such technologies and products once developed,
although effective, are uneconomical to market, that third parties hold
proprietary rights that preclude the Company from marketing such technologies
and products or that third parties market superior or equivalent technologies
and products.
 
    The Company's agreements with licensors do not contain any representations
by the licensors as to the safety or efficacy of the inventions or discoveries
covered thereby. The Company is unable to predict whether the research and
development activities it is funding will result in any commercially viable
products or applications. Further, due to the extended testing required before
marketing clearance can be obtained from the United States Food and Drug
Administration (the "FDA") or other similar agencies, the Company is not able to
predict with any certainty, when, if ever, the Company will be able to
commercialize any of its proposed technologies or products.
 
GOVERNMENT REGULATION; NO ASSURANCE OF PRODUCT APPROVAL
 
    The Company's proposed products and technologies are in very early stages of
development. The research, preclinical development, clinical trials, product
manufacturing and marketing to be conducted by the Company is subject to
regulation by the FDA and similar health authorities in foreign countries. FDA
approval of the Company's products, as well as the manufacturing processes and
facilities, if any, used to produce such products will be required before such
products may be marketed in the U.S. The process of obtaining approvals from the
FDA is costly, time consuming and often subject to unanticipated delays. There
can be no assurance that approvals of the Company's proposed products, processes
or facilities will be granted on a timely basis, or at all. In addition, new
government regulations may be established that could delay or prevent regulatory
approval of the Company's products under development. Any future failure to
obtain or delay in obtaining any such approval will materially and adversely
affect the ability of the Company to market its proposed products and the
business, financial condition and results of operations of the Company.
 
    Even if regulatory approval of the Company's proposed products is granted,
such approval may include significant limitations on indicated uses for which
any such products could be marketed. Further, even if such regulatory approvals
are obtained, a marketed drug or device and its manufacturer are subject to
continued review, and later discovery of previously unknown problems may result
in restrictions on such product or manufacturer, including withdrawal of the
product from the market. Failure of the Company to obtain and maintain
regulatory approval of its proposed products, processes or facilities would have
a material adverse effect on the business, financial condition and results of
operations of the Company.
 
    The Company's proposed products and technologies may also be subject to
certain other federal, state and local government regulations, including, but
not limited to, the Federal Food, Drug and Cosmetic Act, the Environmental
Protection Act, the Occupational Safety and Health Act and state, local and
foreign counterparts to certain of such acts. The Company intends to develop its
business to strategically address regulatory needs. However, the Company cannot
predict the extent of the adverse effect on its business or the financial and
other costs that might result from any government regulations arising out of
future legislative, administrative or judicial action.
 
SECURITIES LAW RESTRICTIONS ON THE EXERCISE OF REDEEMABLE WARRANTS
 
    A holder of Redeemable Warrants will have the right to exercise such
Redeemable Warrants for the purchase of shares of Common Stock only if the
Company has filed with the Securities and Exchange Commission a current
prospectus meeting the requirements of the Securities Act covering the issuance
of such shares of Common Stock issuable upon exercise of the Redeemable Warrants
and only if the issuance of such shares has been registered or qualified, or is
deemed to be exempt from registration or qualification under, the securities
laws of the state of residence of the holder of the Redeemable Warrant. The
Company has undertaken and intends to file and keep effective and current a
prospectus which will permit the purchase and sale of the Common Stock
underlying the Redeemable Warrants, but there can be
 
                                       6

no assurance that the Company will be able to do so. Although the Company
intends to seek to qualify for sale the shares of Common Stock underlying the
Redeemable Warrants in those states in which the securities are to be offered,
no assurance can be given that such qualification will occur. The Redeemable
Warrants may be deprived of any value if a prospectus covering the shares
issuable upon the exercise thereof is not kept effective and current or if such
underlying shares are not, or cannot be, registered in the applicable states.
See "Description of Securities--Redeemable Warrants."
 
DEPENDENCE ON LICENSE AND SPONSORED RESEARCH AGREEMENTS
 
    The Company depends on license agreements that form the basis of its
proprietary technology, and, with the exception of its majority-owned
subsidiary, Optex Opthalmologics, Inc., a Delaware corporation ("Optex"), the
Company relies on sponsored research agreements for its research and development
efforts. The license agreements that have been entered into by the Company
typically require the use of due diligence in developing and bringing products
to market and the payment of certain milestone amounts that in some instances
may be substantial. With the exception of Optex, the Company is also obligated
to make royalty payments on the sales, if any, of products resulting from such
licensed technology and, is responsible for the costs of filing and prosecuting
patent applications and maintaining issued patents. With the exception of Optex,
the Company does not currently have laboratory facilities, and, accordingly,
certain research and development activities of the Company is intended to be
conducted by universities or other institutions pursuant to sponsored research
agreements. The sponsored research agreements entered into and contemplated to
be entered into by the Company generally require periodic payments on an annual,
quarterly or monthly basis.
 
    If the Company does not meet its financial, development or other obligations
under either its license agreements or its sponsored research agreements in a
timely manner, the Company could lose the rights to its proprietary technology
or the right to have the applicable university or institution conduct its
research and development efforts. If the rights of the Company under its license
or sponsored research agreements are terminated, such termination could have a
material adverse effect on the business and research and development efforts of
the Company.
 
UNCERTAINTY REGARDING PATENTS AND PROPRIETARY RIGHTS
 
    The success of the Company will depend in large part on its or its
licensors' ability to obtain patents, defend their patents, maintain trade
secrets and operate without infringing upon the proprietary rights of others,
both in the United States and in foreign countries. The patent position of firms
relying upon biotechnology is highly uncertain and involves complex legal and
factual questions. To date there has emerged no consistent policy regarding the
breadth of claims allowed in biotechnology patents or the degree of protection
afforded under such patents. The Company relies on certain United States patents
and pending United States and foreign patent applications relating to various
aspects of its products and processes. All of these patents and patent
applications are owned by third parties and are licensed or sublicensed to the
Company. The patent application and issuance process can be expected to take
several years and entail considerable expense to the Company, as it is
responsible for such costs under the terms of such license agreements. There can
be no assurance that patents will issue as a result of any such pending
applications or that the existing patents and any patents resulting from such
applications will be sufficiently broad to afford protection against competitors
with similar technology. In addition, there can be no assurance that such
patents will not be challenged, invalidated, or circumvented, or that the rights
granted thereunder will provide competitive advantages to the Company. The
commercial success of the Company will also depend upon avoiding infringement of
patents issued to competitors. A United States patent application is maintained
under conditions of confidentiality while the application is pending, so the
Company cannot determine the inventions being claimed in pending patent
applications filed by its competitors. Litigation may be necessary to defend or
enforce the Company's patent and license rights or to determine the scope and
validity of others' proprietary rights. Defense and enforcement of patent claims
can be expensive and time consuming, even, in those instances in which the
outcome is favorable to the
 
                                       7

Company, and can result in the diversion of substantial resources from the
Company's other activities. An adverse outcome could subject the Company to
significant liabilities to third parties, require the Company to obtain licenses
from third parties, or require the Company to alter its products or processes,
or cease altogether any related research and development activities or product
sales, any of which may have a material adverse effect on the Company's
business, results of operations and financial condition.
 
    The Company has certain licenses from third parties and in the future may
require additional licenses from other parties to develop, manufacture and
market commercially viable products effectively. The Company's commercial
success will depend in part on obtaining and maintaining such licenses. There
can be no assurance that such licenses can be obtained or maintained on
commercially reasonable terms, if at all, that the patents underlying such
licenses will be valid and enforceable or that the proprietary nature of the
patented technology underlying such licenses will remain proprietary.
 
    The Company relies substantially on certain technologies that are not
patentable or proprietary and are therefore available to its competitors. The
Company also relies on certain proprietary trade secrets and know-how that are
not patentable. Although the Company has taken steps to protect its unpatented
trade secrets and know-how, in part through the use of confidentiality
agreements with its employees, consultants and contractors, there can be no
assurance that these agreements will not be breached, that the Company would
have adequate remedies for any breach, or that the Company's trade secrets will
not otherwise become known or be independently developed or discovered by
competitors.
 
    The success of the Company is also dependent upon the skills, knowledge and
experience of its scientific and technical personnel. The management and
scientific personnel of the Company has been recruited primarily from other
scientific companies, pharmaceutical companies and academic institutions. In
some cases, these individuals may be continuing research in the same areas with
which they were involved prior to joining the Company. Although the Company has
not received any notice of any claims and knows of no basis for any claims, it
could be subject to allegations of violation of trade secrets and similar claims
which could, regardless of merit, be time consuming, expensive to defend, and
have a material adverse effect on the Company's business, results of operations
and financial condition.
 
UNCERTAINTY OF PRODUCT PRICING AND REIMBURSEMENT; HEALTH CARE REFORM AND RELATED
  MEASURES
 
    The levels of revenues and profitability of pharmaceutical and/or
biotechnology products and companies may be affected by the continuing efforts
of governmental and third party payors to contain or reduce the costs of health
care through various means and the initiatives of third party payors with
respect to the availability of reimbursement. For example, in certain foreign
markets, pricing or profitability of prescription pharmaceuticals is subject to
government control. In the United States there have been, and the Company
expects that there will continue to be, a number of federal and state proposals
to implement similar governmental control. Although the Company cannot predict
what legislative reforms may be proposed or adopted or what impact actions taken
by federal, state or private payors for health care goods and services in
response to any health care reform proposals or legislation may have on its
business, the existence and pendency of such proposals could have a material
adverse effect on the Company in general. In addition, the Company's ability to
commercialize potential pharmaceutical and/or biotechnology products may be
adversely affected to the extent that such proposals have a material adverse
effect on other companies that are prospective collaborators with respect to any
of the Company's product candidates.
 
    In addition, in both the United States and elsewhere, sales of medical
products and services are dependent in part on the availability of reimbursement
to the consumer from third party payors, such as government and private
insurance plans. Third party payors are increasingly challenging the prices
charged for medical products and services. If the Company succeeds in bringing
one or more products to the market, there can be no assurance that these
products will be considered cost effective and that reimbursement to the
consumer will be available or will be sufficient to allow the Company to sell
its products on a competitive basis.
 
                                       8

DEPENDENCE UPON KEY PERSONNEL AND CONSULTANTS
 
    The Company is highly dependent upon its officers and directors, as well as
its Scientific Advisory Board members, consultants and collaborating scientists.
Atlantic and its subsidiaries have an aggregate of only eight full-time
employees, four of whom are officers of Atlantic, and the loss of any of these
individuals would have a material adverse effect on the Company. Although
Atlantic has entered into employment agreements with each of its officers, such
employment agreements do not contain provisions which would prevent such
employees from resigning their positions with Atlantic at any time. The Company
does not maintain key-man life insurance policies on any of such key personnel.
Each of the Company's non-employee directors, advisors and consultants devotes
only a portion of his or her time to the Company's business. The loss of certain
of these individuals could have a material adverse effect on the Company.
 
    The Company may seek to hire additional personnel. Competition for qualified
employees among pharmaceutical and biotechnology companies is intense, and the
loss of any of such persons, or the inability to attract, retain and motivate
any additional highly skilled employees required for the expansion of the
Company's activities could have a material adverse effect on the Company. There
can be no assurance that the Company will be able to retain its existing
personnel or to attract additional qualified employees.
 
    The Company's scientific advisors are employed on a full time basis by
unrelated employers and some have one or more consulting or other advisory
arrangements with other entities which may conflict or compete with their
obligations to the Company. Inventions or processes discovered by such persons,
other than those to which the licenses may relate, those to which the Company is
able to acquire licenses for or those which were invented while performing
consulting services on behalf of the Company pursuant to a proprietary
information agreement or utilizing the Company's facilities, will not become the
property of the Company, but will remain the property of such persons or of such
persons' full-time employers. Failure to obtain needed patents, licenses or
proprietary information held by others could have a material adverse effect on
the Company.
 
COMPETITION
 
    The Company's business is characterized by intensive research efforts and
intense competition. Many companies, research institutes, hospitals and
universities are working to develop products and technologies in the Company's
fields of research. Most of these entities have substantially greater financial,
technical, manufacturing, marketing, distribution and other resources than the
Company. Certain of such companies have experience in undertaking testing and
clinical trials of new or improved products similar in nature to that which the
Company is developing. In addition, certain competitors have already begun
testing of similar compounds or processes and may introduce such products or
processes before the Company. Accordingly, other companies may succeed in
developing products earlier than the Company or that are more effective than
those proposed to be developed by the Company. Further, it is expected that
competition in the Company's fields will intensify. There can be no assurance
that the Company will be able to compete successfully in the future.
 
DEPENDENCE ON OTHERS FOR CLINICAL DEVELOPMENT OF, REGULATORY APPROVALS FOR AND
  MARKETING OF PHARMACEUTICAL PRODUCTS
 
    The Company currently does not have the resources to directly manufacture,
market or sell any of the Company's proposed products and the Company has no
current plans to acquire such resources. The Company anticipates that it will,
in the future, enter into collaborative agreements with pharmaceutical and/or
biotechnology companies for the development of, clinical testing of, seeking of
regulatory approval for, manufacturing of, marketing of and commercialization of
certain of its proposed products. The Company may in the future grant to its
collaborative partners rights to license and commercialize any
 
                                       9

products developed under these collaborative agreements, and such rights would
limit the Company's flexibility in considering alternatives for the
commercialization of such products. Under such agreements, the Company may rely
on its respective collaborative partners to conduct research efforts and
clinical trials on, obtain regulatory approvals for and manufacture, market and
commercialize certain of its products. The Company expects that the amount and
timing of resources devoted to these activities generally will be controlled by
each such individual partner. The inability of the Company to acquire such third
party manufacturing, distribution, marketing and selling arrangements for such
anticipated products would have a material adverse effect on the Company's
business. There can be no assurance that the Company will be able to enter into
any arrangements for the manufacturing, marketing and selling of its products,
or that, if such arrangements are entered into, such future partners will be
successful in commercializing products or that the Company will derive any
revenues from such arrangements.
 
RISK OF PRODUCT LIABILITY; NO INSURANCE
 
    Should the Company develop and market any products, the marketing of such
products, through third-party arrangements or otherwise, may expose the Company
to product liability claims. The Company presently does not carry product
liability insurance. Upon clinical testing or commercialization of the Company's
proposed products, certain of the licensors require that the Company obtain
product liability insurance. There can be no assurance that the Company will be
able to obtain such insurance or, if obtained, that such insurance can be
acquired in sufficient amounts to protect the Company against such liability or
at a reasonable cost. The Company is required to indemnify the Company's
licensors against any product liability claims incurred by them as a result of
the products developed by the Company. None of the Company's licensors has made,
and are not expected to make, any representations as to the safety or efficacy
of the inventions covered by the licenses or as to any products which may be
made or used under rights granted therein or thereunder.
 
CONTROL BY EXISTING STOCKHOLDERS
 
    Two principal stockholders of the Company beneficially own approximately 27%
of the outstanding shares of Common Stock. Accordingly, such holders, if acting
together, may have the ability to exert significant influence over the election
of the Company's Board of Directors and other matters submitted to the Company's
stockholders for approval. The voting power of these holders may discourage or
prevent any proposed takeover of the Company.
 
NO ASSURANCE OF IDENTIFICATION OF ADDITIONAL PROJECTS
 
    The Company is engaged in the development and commercialization of
biomedical and pharmaceutical products and technologies. From time to time, if
the Company's resources allow, the Company may explore the acquisition and
subsequent development and commercialization of additional biomedical and
pharmaceutical products and technologies. However, there can be no assurance
that the Company will be able to identify any additional products or
technologies and, even if suitable products or technologies are identified, the
Company does not expect to have sufficient resources to pursue any such products
or technologies in the foreseeable future.
 
CERTAIN INTERLOCKING RELATIONSHIPS; POTENTIAL CONFLICTS OF INTEREST
 
    Two of the four members of the Board of Directors and one of the officers of
the Company are full-time or part-time officers of Paramount Capital
Investments, LLC a New York-based merchant banking and venture capital firm
specializing in biotechnology companies ("Investments"). In the regular course
of its business, Investments identifies, evaluates and pursues investment
opportunities in biomedical and pharmaceutical products, technologies and
companies. Generally, Delaware corporate law requires that any transactions
between the Company and any of its affiliates be on terms that, when taken as a
whole, are substantially as favorable to the Company as those then reasonably
obtainable from a person who is
 
                                       10

not an affiliate in an arms-length transaction. Nevertheless, neither
Investments nor any such directors are obligated pursuant to any agreement or
understanding with the Company to make any additional products or technologies
available to the Company, nor can there be any assurance, and the Company does
not expect and security holders should not expect, that any biomedical or
pharmaceutical product or technology identified by Investments or any such
directors in the future will be made available to the Company. In addition,
certain of the officers and directors of the Company may from time to time serve
as officers or directors of other biopharmaceutical or biotechnology companies.
There can be no assurance that such other companies will not, in the future,
have interests in conflict with those of the Company.
 
    The Company has entered into several agreements with Investments pursuant to
which Investments provides financial advisory services to the Company.
 
   
    Michael S. Weiss, the Company's Secretary, is a Senior Managing Director of
Paramount Capital, Inc., the placement agent for the Company's private placement
of its Series A Preferred Stock (the "Placement Agent"). See "Recent
Developments." Lindsay A. Rosenwald, M.D., a principal stockholder of the
Company, is the President and sole stockholder of the Placement Agent and of
Investments.
    
 
RISKS ASSOCIATED WITH LITIGATION
 
    In November 1996 and February 1997, related complaints alleging claims under
the Securities Exchange Act of 1934, as amended, and common law causes of action
were filed against the Company in the United States District Court for the
District of Delaware and the Delaware Chancery Court, respectively. The parties
have reached a settlement with respect to such complaints, pursuant to which an
existing stockholder of the Company owning greater than five percent of the
Company's capital stock transferred to plaintiff an aggregate of 5,000 shares of
the Company's Common Stock.
 
NO DIVIDENDS
 
    The Company has not paid any cash dividends on its Common Stock since its
formation and does not anticipate paying any cash dividends in the foreseeable
future. Management anticipates that all earnings and other resources of the
Company, if any, will be retained by the Company for investment in its business.
 
POSSIBLE DELISTING FROM NASDAQ AND MARKET ILLIQUIDITY
 
    Although the Common Stock is quoted on Nasdaq, continued inclusion of such
securities on Nasdaq will require that (i) the Company maintain at least
$2,000,000 in total assets and $1,000,000 in capital and surplus, (ii) the
minimum bid price for the Common Stock be at least $1.00 per share, (iii) the
public float consist of at least 100,000 shares of Common Stock, valued in the
aggregate at more than $200,000, (iv) the Common Stock have at least two active
market makers and (v) the Common Stock be held by at least 300 holders. If the
Company is unable to satisfy such maintenance requirements, the Company's
securities may be delisted from Nasdaq. In such event, trading, if any, in the
Common Stock would thereafter be conducted in the over-the-counter market in the
"pink sheets" or the National Association of Securities Dealers' "Electronic
Bulletin Board." Consequently, the liquidity of the Company's securities could
be materially impaired, not only in the number of securities that can be bought
and sold at a given price, but also through delays in the timing of transactions
and reduction in security analysts' and the media's coverage of the Company,
which could result in lower prices for the Company's securities than might
otherwise be attained and could also result in a larger spread between the bid
and asked prices for the Company's securities.
 
    In addition, if the Common Stock is delisted from trading on Nasdaq and the
trading price of the Common Stock is less than $5.00 per share, trading in the
Common Stock would also be subject to the requirements of Rule 15g-9 promulgated
under the Exchange Act. Under such rule, broker/dealers who recommended such
low-priced securities to persons other than established customers and accredited
investors must satisfy special sales practice requirements, including a
requirement that they make an
 
                                       11

individualized written suitability determination for the purchaser and receive
the purchaser's written consent prior to the transaction. The Securities
Enforcement Remedies and Penny Stock Reform Act of 1990 also requires additional
disclosure in connection with any trades involving a stock defined as a penny
stock (generally, according to recent regulations adopted by the Commission, any
equity security not traded on an exchange or quoted on Nasdaq that has a market
price of less than $5.00 per share, subject to certain exceptions), including
the delivery, prior to any penny stock transaction, of a disclosure schedule
explaining the penny stock market and the risks associated therewith. Such
requirements could severely limit the market liquidity of the Common Stock.
There can be no assurance that the Common Stock will not be delisted or treated
as penny stock.
 
LIQUIDITY OF INVESTMENT
 
    The Company's securities are traded on Nasdaq and the Company's securities
lack the liquidity of securities traded on the principal trading markets.
Accordingly, an investor may be unable to promptly liquidate an investment in
the Common Stock.
 
POSSIBLE VOLATILITY OF STOCK PRICE
 
    The market price of the Company's securities, like the stock prices of many
publicly traded biotechnology and smaller pharmaceutical companies, has been and
may continue to be highly volatile.
 
ENVIRONMENTAL REGULATION
 
    In connection with its research and development activities, the Company is
subject to federal, state and local laws, rules, regulations and policies
governing the use, generation, manufacture, storage, air emission, effluent
discharge, handling and disposal of certain materials and wastes. Although the
Company believes that it has complied with these laws and regulations in all
material respects and has not been required to take any action to correct any
noncompliance, there can be no assurance that the Company will not be required
to incur significant costs to comply with environmental and health and safety
regulations in the future.
 
POSSIBLE ADVERSE EFFECT OF SHARES ELIGIBLE FOR FUTURE SALE
 
    Future sales by existing stockholders could adversely affect the prevailing
market price of the Company's Common Stock. The outstanding shares of the
Company's Common Stock are all freely tradeable, subject to volume and other
restrictions imposed by Rule 144 under the Securities Act with respect to sales
by affiliates of the Company. An 18-month restriction on transfer applicable to
the shares of Common Stock now owned or hereafter acquired by the Company's
officers, directors and certain stockholders expired on June 14, 1997. Sales of
substantial amounts of Common Stock may have an adverse effect on the market
price of the Company's Common Stock.
 
    In connection with the Company's initial public offering, the Company
granted to Joseph Stevens & Company, L.P., the underwriter that managed the
Company's initial public offering (the "Underwriter"), warrants to purchase from
the Company 165,000 units, each consisting of one share of Common Stock and one
redeemable warrant to purchase one share of Common Stock at an initial exercise
price of $6.60 per unit. Such warrants are exercisable during the four year
period commenced December 13, 1996. The redeemable warrants issuable upon
exercise of these warrants have an exercise price of $6.05 per share. As long as
the warrants remain unexercised, the terms under which the Company could obtain
additional capital may be adversely affected. The Company granted to holders of
the warrants issued to such Underwriter the right on two occasions (one at the
expense of the Company) to file a registration statement under the Securities
Act covering the securities underlying such warrants and the additional right to
include such securities in any registration filed by the Company under the
Securities Act.
 
                                       12

    No prediction can be made as to the effect, if any, that sales of Units,
Redeemable Warrants and/or Common Stock or the availability of such securities
for sale will have on the market prices prevailing from time to time for the
Units, the Redeemable Warrants and/or the Common Stock. Nevertheless, the
possibility that substantial amounts of such securities may be sold in the
public market may adversely affect prevailing market prices for the Company's
equity securities and could impair the Company's ability to raise capital in the
future through the sale of equity securities.
 
ANTITAKEOVER EFFECTS OF PROVISIONS OF THE CERTIFICATE OF INCORPORATION AND
  DELAWARE LAW
 
    Atlantic's Certificate of Incorporation authorizes the issuance of shares of
"blank check" Preferred Stock. The Board of Directors has the authority to issue
the Preferred Stock in one or more series and to fix the relative rights,
preferences and privileges and restrictions thereof, including dividend rights,
dividend rates, conversion rights, voting rights, terms of redemption,
redemption prices, liquidation preferences and the number of shares constituting
any series or the designation of such series. The issuance of Preferred Stock
may have the effect of delaying, deferring or preventing a change in control of
the Company without further action by the stockholders of the Company. The
issuance of Preferred Stock with voting and conversion rights may adversely
affect the voting power of the holders of the Common Stock, including the loss
of voting control to others.
 
    The Company is subject to Section 203 of the Delaware General Corporation
Law which, subject to certain exceptions, prohibits a Delaware corporation from
engaging in any business combination with any interested stockholder for a
period of three years following the date that such stockholder became an
interested stockholder. In general, Section 203 defines an interested
stockholder as any entity or person beneficially owning 15% or more of the
outstanding voting stock of the corporation and any entity or person affiliated
with or controlling or controlled by such entity or person. The foregoing
provisions could have the effect of discouraging others from making tender
offers for the Company's shares and, as a consequence, they also may inhibit
fluctuations in the market price of the Company's shares that could result from
actual or rumored takeover attempts. Such provisions also may have the effect of
preventing changes in the management of the Company.
 
                                       13

                              RECENT DEVELOPMENTS
 
   
    On May 22, 1997 and August 7, 1997, the Company completed private placements
(the "Private Placement") of an aggregate of 123.72 units, each unit consisting
of 10,000 shares of the Company's Series A Convertible Preferred Stock (the
"Series A Preferred"), for gross proceeds of approximately $12,372,000.
Paramount Capital, Inc., a New York-based merchant and investment banking firm
specializing in the biotechnology industry ("Paramount" or the "Placement
Agent"), acted as placement agent for the Private Placement. Michael S. Weiss,
the Company's Secretary, is a Senior Managing Director of the Placement Agent,
and Lindsay A. Rosenwald, M.D., a principal stockholder of the Company, is the
President and sole stockholder of the Placement Agent.
    
 
    In connection with the Private Placement, the Company paid to the Placement
Agent compensation in the form of cash commissions and a non-accountable expense
allowance equal to nine percent and four percent, respectively, of the gross
proceeds received by the Company from the sale of the units. In addition, the
Company agreed to sell to Paramount or its designees, for $0.001 per share,
warrants (the "Placement Warrants") to purchase an aggregate of 123,720 shares
of Series A Preferred. For a description of the terms of the Series A Preferred
issued in the Private Placement and of the Placement Warrants, see "Description
of Securities--Preferred Stock--Series A Convertible Preferred Stock" and
"Description of Securities--Placement Warrants."
 
    Also in connection with the Private Placement, the Company and the Placement
Agent agreed to enter into a financial advisory agreement (the "Agreement")
pursuant to which the Placement Agent will act as the Company's non-exclusive
financial advisor. Such engagement will provide that the Placement Agent receive
(i) a monthly retainer of $4,000 commencing on the first of the month following
the date of the Agreement (with a minimum engagement of 24 months), (ii)
out-of-pocket expenses incurred in connection with services performed under the
Agreement and (iii) standard success fees in the event the Placement Agent
assists the Company in connection with certain financing and strategic
transactions.
 
                                       14

                            SELLING SECURITYHOLDERS
 
    The following table sets forth certain information, as of the date hereof,
with respect to the number of shares of Common Stock beneficially owned by each
of the Selling Securityholders and as adjusted to give effect to the sale of the
Shares offered hereby. Beneficial ownership of the shares offered hereby by such
Selling Securityholders will depend on the number of shares sold by each Selling
Securityholder in this offering. The Shares are being registered to permit
public secondary trading of the Shares, and the Selling Securityholders may
offer the Shares for resale from time to time. Except as indicated in this
Prospectus, none of the Selling Securityholders has had a material relationship
with the Company within the past three years other than as a result of the
ownership of the Shares or other securities of the Company. See "Plan of
Distribution."
 
    The Shares offered by this Prospectus may be offered from time to time by
the Selling Securityholders named below:
 


                                                             NUMBER OF SHARES OWNED
                                                              PRIOR TO OFFERING(1)     NUMBER OF     OWNERSHIP AFTER OFFERING(1)
                                                            ------------------------    SHARES
                                                             NUMBER OF                   BEING     --------------------------------
NAME AND ADDRESS OF NUMBER OF SELLING SECURITYHOLDER          SHARES       PERCENT      OFFERED    NUMBER OF SHARES      PERCENT
- ----------------------------------------------------------  -----------  -----------  -----------  -----------------  -------------
                                                                                                       
Dreyfus Growth and Value Funds, Inc., a Maryland
  corporation,--Dreyfus Aggressive Growth Fund(2)
    200 Park Avenue
    New York, NY 10166....................................     140,000         4.64%     140,000               0                0%
Premier Strategic Growth Fund(2), a Massachusetts Business
  Trust (2)
    200 Park Avenue
    New York, NY 10166....................................     110,000         3.65%     110,000               0                0%
                                                                                      -----------
        TOTAL.............................................                               250,000
                                                                                      -----------
                                                                                      -----------

 
- ------------------------
 
(1) Percentage of beneficial ownership is calculated assuming 3,016,920 shares
    of Common Stock were outstanding as of June 30, 1997. Beneficial ownership
    is determined in accordance with the rules of the Securities and Exchange
    Commission and generally includes voting or investment power with respect to
    securities. Shares of Common Stock subject to options or warrants currently
    exercisable or convertible, or exercisable or convertible within 60 days of
    June 30, 1997, are deemed outstanding for computing the percentage of the
    person holding such option or warrant but are not deemed outstanding for
    computing the percentage of any other person. Except as indicated in the
    footnotes to this table and pursuant to applicable community property laws,
    the persons named in the table have sole voting and investment power with
    respect to all shares of Common Stock beneficially owned.
 
(2) The Dreyfus Corporation serves as the investment advisor for each of Dreyfus
    Growth and Value Funds, Inc., a Maryland corporation,--Dreyfus Aggressive
    Growth Fund and Premier Strategic Growth Fund, a Massachusetts Business
    Trust, and as such may be considered the beneficial owner of the shares of
    Common Stock held by such funds.
 
                              PLAN OF DISTRIBUTION
 
    The Shares offered by the Selling Securityholders are not being
underwritten. The Company will receive no proceeds from the sale of the Shares.
The Shares offered hereby may be sold by the Selling Securityholders from time
to time in transactions (which may include block transactions) in the over-the-
counter market, in negotiated transactions, or a combination of such methods of
sale, at fixed prices that may be changed, at market prices prevailing at the
time of sale, or at negotiated prices. The Selling Securityholders may effect
such transactions by selling the Shares directly to purchasers or through
broker-
 
                                       15

dealers that may act as agents or principals. Such broker-dealers may receive
compensation in the form of discounts, concessions or commissions from the
Selling Securityholders and/or the purchasers of the Shares for whom such
broker-dealers may act as agents or to whom they sell as principals, or both
(which compensation as to a particular broker-dealer might be in excess of
customary commissions).
 
    The Dreyfus Corporation serves as the investment advisor for each of Dreyfus
Growth and Value Funds, Inc., a Maryland corporation,--Dreyfus Aggressive Growth
Fund ("Value Fund") and Premier Strategic Growth Fund, a Massachusetts business
trust ("Growth Fund"), and as such may be considered the beneficial owner of the
shares of Common Stock held by such funds. Value Fund and Growth Fund together
own an aggregate of eight percent of the Company's capital stock, and therefore
either fund or The Dreyfus Corporation may be deemed affiliates of the Company.
Other than the foregoing, there are no material relationships between any of the
Selling Securityholders and the Company or any of its predecessors or
affiliates.
 
    The Selling Securityholders and any broker-dealers that act in connection
with the sale of the Shares as principals may be deemed to be "underwriters"
within the meaning of Section 2(11) of the Securities Act and any commission
received by them and any profit on the resale of such securities as principals
might be deemed to be underwriting discounts and commissions under the
Securities Act. The Selling Securityholders may agree to indemnify any agent,
dealer or broker-dealer that participates in transactions involving sales of
such securities against certain liabilities, including liabilities arising under
the Securities Act. The Company will not receive any proceeds from the sales of
the Shares. Sales of the Shares by the Selling Securityholders, or even the
potential of such sales, would likely have an adverse effect on the market price
of the Company's outstanding Units, Common Stock and Redeemable Warrants.
 
    At the time a particular offer of securities is made by or on behalf of the
Selling Securityholder, to the extent required, a prospectus will be distributed
which will set forth the number of securities being offered and the terms of the
offering, including the name or names of any underwriters, dealers or agents, if
any, the purchase price paid by any underwriter for securities purchased from
the Selling Securityholder and any discounts, commissions or concessions allowed
or reallowed or paid to dealers.
 
    In order to comply with the securities laws of certain states, if
applicable, the Shares will be sold in such jurisdictions only through
registered or licensed brokers or dealers. In addition, in certain states the
Shares may not be sold unless they have been registered or qualified for sale in
the applicable state or an exemption from the registration or qualification
requirement is available and is complied with.
 
    Under applicable rules and regulations under the Exchange Act, any person
engaged in the distribution of the Shares may not simultaneously engage in
market making activities with respect to the securities of the Company for a
period of two business days prior to the commencement of such distribution. In
addition and without limiting the foregoing, each Selling Securityholder will be
subject to applicable provisions of the Exchange Act and the rules and
regulations thereunder, including, without limitation, the Rules promulgated
under Regulation M, which provisions may limit the timing of purchases and sales
of shares of the Shares by the Selling Securityholders.
 
    The Shares were originally issued to the Selling Securityholders pursuant to
an exemption from the registration requirements of the Securities Act provided
by Section 4(2) thereof. The Company agreed to register the Shares under the
Securities Act and to indemnify and hold such Selling Securityholders harmless
against certain liabilities under the Securities Act that could arise in
connection with the sale by such Selling Securityholders of the Shares. The
Company has agreed to pay all reasonable fees and expenses incident to the
preparation and filing of this Prospectus and the Registration Statement on Form
S-3 of which it is a part.
 
                                       16

                           DESCRIPTION OF SECURITIES
 
    The authorized capital stock of the Company consists of 80,000,000 shares of
Common Stock and 50,000,000 shares of Preferred Stock.
 
UNITS
 
    As of June 30, 1997, there were 1,872,750 Units outstanding. Each Unit
consists of one share of Common Stock and one Redeemable Warrant. The securities
included in each Unit trade separately.
 
COMMON STOCK
 
    As of June 30, 1997, there were 3,016,920 shares of Common Stock
outstanding, which include the shares of Common Stock composing the Units. In
addition, as of June 30, 1997, there were outstanding options to purchase
699,155 shares of Common Stock at exercise prices ranging from $0.001 to $7.50
per share. Such options expire on various dates through August 15, 2006.
 
    The holders of Common Stock are entitled to one vote per share on all
matters to be voted upon by the stockholders. Subject to preferences that may be
applicable to any outstanding Preferred Stock, the holders of Common Stock are
entitled to receive ratably such dividends, if any, as may be declared from time
to time by the Company's Board of Directors out of funds legally available
therefor. In the event of the liquidation, dissolution or winding up of the
Company, the holders of Common Stock are entitled to share ratably in all assets
remaining after payment of liabilities, subject to prior distribution rights of
Preferred Stock, if any, then outstanding. The Common Stock has no preemptive or
conversion rights or other subscription rights. There are no redemption or
sinking fund provisions applicable to the Common Stock. All outstanding shares
of Common Stock are fully paid and nonassessable, and the shares of Common Stock
to be issued upon completion of the Offering will be fully paid and
nonassessable.
 
PREFERRED STOCK
 
    The Company's Certificate of Incorporation authorizes 50,000,000 shares of
Preferred Stock. The Company's Board of Directors has the authority to issue
Preferred Stock in one or more series and to fix the relative rights,
preferences and privileges and restrictions thereof, including dividend rights,
dividend rates, conversion rights, voting rights, terms of redemption,
redemption prices, liquidation preferences and the number of shares constituting
any series or the designation of such series. The issuance of Preferred Stock
may have the effect of delaying, deferring or preventing a change in control of
the Company without further action by the stockholders of the Company. The
issuance of Preferred Stock with voting and conversion rights may adversely
affect the voting power of the holders of the Common Stock, including the loss
of voting control to others. See "Risk Factors--Need for Additional Financing;
Issuance of Securities by the Operating Companies; Future Dilution" and
"--Antitakeover Effects of Provisions of the Certificate of Incorporation and
Delaware Law."
 
    SERIES A CONVERTIBLE PREFERRED STOCK
 
    The Company has designated 1,375,000 shares of Preferred Stock as "Series A
Convertible Preferred Stock" (the "Series A Preferred"). As of August 15, 1997,
there were outstanding 1,237,200 shares of Series A Preferred and warrants to
purchase 123,720 shares of Series A Preferred. The following is a brief summary
of the rights, preferences and privileges of the Series A Preferred. A complete
description of the rights, preferences and privileges of the Series A Preferred
is set forth in the Company's Certificate of Designation with respect thereto.
 
    DIVIDENDS.  Holders of Series A Preferred will be entitled to receive
dividends as, when and if declared by the Board of Directors. Commencing on
August 7, 1998, holders of Series A Preferred will be entitled to a cumulative
payment-in-kind dividend (the "PIK Dividend") payable in additional shares of
 
                                       17

Series A Preferred at the rate of 10% per annum of the Dividend Base Amount,
payable semi-annually, unless their shares of Series A Preferred have previously
been converted into Common Stock. The Dividend Base Amount shall be $13.00 plus
accrued and unpaid dividends (subject to antidilution adjustment), and
represents a premium to the holders of Series A Preferred of 30% over the $10.00
per share purchase price. The Company shall not declare any dividend or
distribution on any other capital stock of the Company unless and until a
special dividend or distribution of $13.00 per share (subject to appropriate
adjustment to reflect any stock split, combination, reclassification or
reorganization of the Series A Preferred) has been declared and paid on the
Series A Preferred. No dividend or distribution, as the case may be, shall be
declared or paid on any junior stock unless the same dividend is paid to holders
of Series A Preferred. The Company does not intend to pay cash dividends on the
Series A Preferred or the underlying Common Stock for the foreseeable future.
 
    CONVERSION.  Each share of Series A Preferred is convertible at the option
of the holder thereof, at any time after the issuance thereof, into shares of
Common Stock initially at a conversion price equal to $4.72. The conversion
price is subject to adjustment upon the occurrence of certain events, including
the issuance of Common Stock at a per share price less than the conversion
price, or the occurrence of a merger, reorganization, consolidation,
reclassification, stock dividend or stock split which will result in an increase
or decrease in the number of Shares of Common Stock outstanding. Unless
converted earlier, the Company may, at any time on or after August 7, 1998, at
its option, cause the conversion of the Series A Preferred, in whole or in part,
on a PRO RATA basis, into shares of Common Stock at the conversion price in
effect at that time if the closing bid price of the Common Stock has exceeded
200% of the then applicable conversion price for at least 20 trading days in any
30 consecutive trading day period ending three days prior to the date of notice
of conversion.
 
    LIQUIDATION PREFERENCE.  Upon (i) a liquidation, dissolution or winding up
of the Company, whether voluntary or involuntary, (ii) a sale or other
disposition of all or substantially all of the assets of the Company or (iii)
any consolidation, merger, combination, reorganization or other transaction in
which the Company is not the surviving entity or in which the shares of Common
Stock constituting in excess of 50% of the voting power of the Company are
exchanged for or changed into other stock or securities, cash and/ or any other
property, after payment or provision for payment of the debts and other
liabilities of the Company, the holders of the Series A Preferred then
outstanding will first be entitled to receive, PRO RATA (on the basis of the
number of shares of the Series A Preferred then outstanding), and in preference
to the holders of the Common Stock and any capital stock of the Company, an
amount per share equal to $13.00 plus accrued but unpaid dividends, if any,
which in certain circumstances may be paid in securities of another corporation.
 
    VOTING RIGHTS.  The holders of shares of Series A Preferred have the right
at all meetings of stockholders of the Company to that number of votes equal to
the number of shares of Common Stock issuable upon conversion of the Series A
Preferred at the record date for determination of the stockholders entitled to
vote on such matters or, if no such record date is established, at the date such
vote is taken. So long as at least 50% of the shares of Series A Preferred
remain outstanding, the affirmative vote or consent of the holders of 66.67% of
the shares of Series A Preferred shall be necessary to permit, effect or
validate any one or more of the following: (i) the amendment of the Certificate
of Incorporation or Bylaws of the Company if it adversely affects the relative
rights of the holders of the Series A Preferred, (ii) the declaration or payment
of a dividend on any securities of the Company other than the Series A Preferred
or the authorization of the repurchase of any securities of the Company, (iii)
the issuance of any security ranking senior to or on a parity with the Series A
Preferred with respect to (A) a liquidation event, (B) the payment of dividends
or (C) voting rights (except class voting rights required by law), (iv) any
liquidation, dissolution or sale of substantially all of the assets of the
Company, (v) the incorporation of any subsidiary company and (vi) the issuance
of any debt securities or incurrence of indebtedness for borrowed money in
excess of $1,000,000, PROVIDED, HOWEVER, that any issuance of debt securities or
incurrence of indebtedness
 
                                       18

for borrowed money in excess of $500,000 shall be approved by a supermajority of
the Board of Directors of the Company.
 
REDEEMABLE WARRANTS
 
    The Redeemable Warrants were issued in the Company's initial public offering
pursuant to a warrant agreement (the "Redeemable Warrant Agreement") among
Joseph Stevens & Company, L.P. (the "Underwriter"), the Company and Continental
Stock Transfer & Trust Company (the "Warrant Agent"), and are evidenced by
warrant certificates in registered form. The following summary is qualified in
its entirety by the text of the Redeemable Warrant Agreement, a copy of which
has been filed as an exhibit to the Registration Statement.
 
    Each Redeemable Warrant entitles the registered holder thereof to purchase
one share of Common Stock at a price of $5.50 per share, subject to adjustment,
commencing on the date of issuance. The Redeemable Warrants expire on December
13, 2000 (the "Expiration Date"). As of December 14, 1996 the Redeemable
Warrants are subject to redemption by the Company at a redemption price of $0.05
per Redeemable Warrant on 30 days' prior written notice, provided that the
average closing bid price (or last sales price) of the Common Stock as reported
on Nasdaq (or on such exchange on which the Common Stock is then traded) equals
or exceeds $8.25 per share, subject to adjustment, for any 20 trading days
within a period of 30 consecutive trading days ending on the fifth trading day
prior to the date of notice of redemption. The holder of a Redeemable Warrant
will lose his right to purchase if such right is not exercised prior to
redemption by the Company on the date for redemption specified in the Company's
notice of redemption or any later date specified in a subsequent notice. Notice
of redemption by the Company shall be given by first class mail to the holders
of the Redeemable Warrants at their addresses set forth in the Company's
records.
 
    The exercise price of the Redeemable Warrants and the number and kind of
shares of Common Stock or other securities and property to be obtained upon
exercise of the Redeemable Warrants are subject to adjustment in certain
circumstances including a stock split of, or stock division, combination or
recapitalization of, the Common Stock. Additionally, an adjustment would be made
upon the consolidation of the Company with or the merger of the Company with or
into another corporation (other than a consolidation or merger which does not
result in any reclassification or change of the outstanding Common Stock) so as
to enable Redeemable Warrant holders to purchase the kind and number of shares
of stock or other securities or property (including cash) receivable in such
event by a holder of the number of shares of Common Stock that might otherwise
have been purchased upon exercise of such Redeemable Warrant. No adjustment for
cash dividends, if any, will be made upon exercise of the Redeemable Warrants.
 
    The exercise price of the Redeemable Warrants bears no relation to any
objective criteria of value and should not be regarded as an indication of the
future market price of the securities offered hereby. The Redeemable Warrants do
not confer upon the holder any voting or any other rights of a stockholder of
the Company. Upon notice to the Redeemable Warrant holders, the Company has the
right to reduce the exercise price or extend the expiration date of the
Redeemable Warrants.
 
    The Redeemable Warrants may be exercised upon surrender of the Redeemable
Warrant certificate on or prior to the expiration date (or earlier redemption
date) of such Redeemable Warrant at the offices of the Warrant Agent, with the
form of "Election to Purchase" on the reverse side of the Redeemable Warrant
certificate completed and executed as indicated, accompanied by payment of the
full exercise price (by cashier's or certified check payable to the order of the
Warrant Agent) for the number of Redeemable Warrants being exercised. The
Redeemable Warrants will become void and of no value upon the Expiration Date. A
holder may sell the Redeemable Warrants instead of exercising them. There can be
no assurance, however, that a market for the Redeemable Warrants will continue.
If a prospectus covering the shares of Common Stock issuable upon the exercise
of Redeemable Warrants is not kept effective and current or if such shares are
not qualified for sale in certain states, holders of Redeemable Warrants
 
                                       19

desiring to exercise the Redeemable Warrants will have no choice but either to
sell such Redeemable Warrants or let them expire. See "Risk Factors--Securities
Law Restrictions on the Exercise of Redeemable Warrants."
 
    The Redeemable Warrant Agreement provides that it may be amended at any time
with the written consent of registered holders representing at least 66 2/3% of
the Redeemable Warrants then outstanding.
 
UNDERWRITER'S WARRANTS
 
    In connection with the Company's initial public offering, the Company sold
to the Underwriter, for nominal consideration, Underwriter's Warrants to
purchase from the Company 165,000 Units. The Underwriter's Warrants are
initially exercisable at a price equal to $6.60 and may be exercised at any time
during the four year period commenced December 14, 1996. The shares of Common
Stock and Redeemable Warrants issuable upon exercise of the Underwriter's
Warrants are identical to those offered to the public pursuant to the Unit
Offering, except that the Redeemable Warrants issuable upon exercise of the
Underwriter's Warrants have an exercise price of $6.05 per share and such
Redeemable Warrants have not been approved for quotation on Nasdaq. The
Underwriter's Warrants contain anti-dilution provisions providing for adjustment
of the number of warrants and exercise price under certain circumstances. The
Underwriter's Warrants grant to the holders thereof certain rights of
registration for the securities issuable upon exercise of the Underwriter's
Warrants.
 
PLACEMENT WARRANTS
 
    In connection with the Private Placement, the Company sold to the Placement
Agent, for nominal consideration, Placement Warrants to purchase from the
Company 123,720 shares of Series A Preferred. The Placement Warrants are
initially exercisable at a price equal to $11.00 per share and may be exercised
at any time during the 10-year period commencing February 7, 1998. The rights,
preferences and privileges of the shares of Series A Preferred issuable upon
exercise of the Placement Warrants are identical to those offered to the
participants in the Private Placement. The Placement Warrants contain
anti-dilution provisions providing for adjustment of the number of securities
underlying the Series A Preferred issuable upon exercise of the Placement
Warrants and the exercise price of the Placement Warrants under certain
circumstances. The Placement Warrants are not redeemable and will remain
outstanding, to the extent not exercised, notwithstanding any mandatory
redemption or conversion of the Series A Preferred underlying the Placement
Warrants. The Placement Warrants grant to the holders thereof certain rights of
registration for the securities issuable upon exercise of the Placement
Warrants. See "--Registration Rights."
 
REGISTRATION RIGHTS
 
    In connection with the Private Placement, the Company has agreed to use its
best efforts to (i) on or prior to September 8, 1997, file with the Commission a
registration statement with respect to the Common Stock issuable upon conversion
of the Series A Preferred, including the Series A Preferred issuable upon
exercise of the Placement Warrants, and (ii) cause such registration statement
to remain effective until the date the holders of the Series A Preferred have
completed the distribution of such securities or until such earlier time as such
shares are no longer, by reason of Rule 144(k) promulgated under the Securities
Act, required to be registered for the sale thereof by such holders.
 
    In addition to the Series A Preferred issued in the Private Placement, the
Company may include in such registration statement up to an additional 788,951
shares of Common Stock covered by piggyback registration rights granted by the
Company to Lindsay A. Rosenwald, M.D., a principal stockholder of the Company
and the President and sole stockholder of the Placement Agent and of VentureTek,
L.P., a principal stockholder of the Company.
 
                                       20

ANTITAKEOVER EFFECTS OF PROVISIONS OF DELAWARE LAW
 
    The Company is subject to Section 203 of the Delaware General Corporation
Law ("Section 203"), which, subject to certain exceptions, prohibits a Delaware
corporation from engaging in any business combination with any interested
stockholder for a period of three years following the date that such stockholder
became an interested stockholder, unless: (i) prior to such date, the board of
directors of the corporation approved either the business combination or the
transaction that resulted in the stockholder becoming an interested stockholder;
(ii) upon consummation of the transaction that resulted in the stockholder
becoming an interested stockholder, the interested stockholder owned at least
85% of the voting stock of the corporation outstanding at the time the
transaction commenced, excluding for purposes of determining the number of
shares outstanding those shares owned (x) by persons who are directors and also
officers and (y) by employee stock plans in which employee participants do not
have the right to determine confidentially whether shares held subject to the
plan will be tendered in a tender or exchange offer; or (iii) on or subsequent
to such date, the business combination is approved by the board of directors and
authorized at an annual or special meeting of stockholders, and not by written
consent, by the affirmative vote of at least 66 2/3% of the outstanding voting
stock that is not owned by the interested stockholder.
 
    Section 203 defines business combination to include: (i) any merger or
consolidation involving the corporation and the interested stockholder; (ii) any
sale, transfer, pledge or other disposition of 10% or more of the assets of the
corporation involving the interested stockholder; (iii) subject to certain
exceptions, any transaction that results in the issuance or transfer by the
corporation of any stock of the corporation to the interested stockholder; (iv)
any transaction involving the corporation that has the effect of increasing the
proportionate share of the stock of any class or series of the corporation
beneficially owned by the interested stockholder; or (v) the receipt by the
interested stockholder of the benefit of any loans, advances, guarantees,
pledges or other financial benefits provided by or through the corporation. In
general, Section 203 defines an interested stockholder as any entity or person
beneficially owning 15% or more of the outstanding voting stock of the
corporation and any entity or person affiliated with or controlling or
controlled by such entity or person.
 
TRANSFER AGENT, REGISTRAR AND WARRANT AGENT
 
    The Transfer Agent and Registrar for the Shares is Continental Stock
Transfer & Trust Company ("CST&T"), 2 Broadway, New York, New York 10004. CST&T
can be reached at (212) 509-4000. CST&T is also the Warrant Agent for the
Redeemable Warrants.
 
                                 LEGAL MATTERS
 
    Certain legal matters with respect to the validity of the Shares offered
hereby are being passed upon for the Company by Brobeck, Phleger & Harrison LLP,
Palo Alto, California.
 
                                    EXPERTS
 
    The consolidated financial statements of the Company appearing in the
Company's Annual Report on Form 10-KSB for the year ended December 31, 1996, for
each of the years in the three-year period ended December 31, 1996, and for the
period from July 13, 1993 (inception) to December 31, 1996, have been
incorporated by reference herein in reliance upon the report of KPMG Peat
Marwick LLP ("KPMG"), independent certified public accountants, and upon the
authority of such firm as experts in accounting and auditing. The report of KPMG
covering the consolidated financial statements referred to above contains an
explanatory paragraph that states that the Company has suffered recurring losses
from operations and has limited capital resources which raise substantial doubt
about its ability to continue as a going concern. The consolidated financial
statements do not include any adjustments that might result from the outcome of
that uncertainty.
 
                                       21

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    NO DEALER, SALESPERSON OR ANY OTHER PERSON HAS BEEN AUTHORIZED TO GIVE ANY
INFORMATION OR TO MAKE ANY REPRESENTATIONS OTHER THAN THOSE CONTAINED IN THIS
PROSPECTUS, AND, IF GIVEN OR MADE, SUCH INFORMATION OR REPRESENTATIONS MUST NOT
BE RELIED UPON AS HAVING BEEN AUTHORIZED BY THE COMPANY. NEITHER THE DELIVERY OF
THIS PROSPECTUS NOR ANY SALE MADE HEREUNDER SHALL, UNDER ANY CIRCUMSTANCES,
CREATE ANY IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE AFFAIRS OF THE
COMPANY OR THAT THE INFORMATION CONTAINED HEREIN IS CORRECT AS OF ANY TIME
SUBSEQUENT TO THE DATE HEREOF. THIS PROSPECTUS DOES NOT CONSTITUTE AN OFFER TO
SELL OR A SOLICITATION FOR AN OFFER TO BUY ANY SECURITIES OFFERED HEREBY BY
ANYONE IN ANY JURISDICTION IN WHICH SUCH OFFER OR SOLICITATION IS NOT AUTHORIZED
OR IN WHICH THE PERSON MAKING SUCH OFFER OR SOLICITATION IS NOT QUALIFIED TO DO
SO OR TO ANYONE TO WHOM IT IS UNLAWFUL TO MAKE SUCH OFFER OR SOLICITATION.
 
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                               TABLE OF CONTENTS
 
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                                                                            PAGE
                                                                            ----
                                                                         
Available Information.....................................................     2
Information Incorporated by Reference.....................................     2
Risk Factors..............................................................     4
Recent Developments.......................................................    14
Selling Securityholders...................................................    15
Plan of Distribution......................................................    15
Description of Securities.................................................    17
Legal Matters.............................................................    21
Experts...................................................................    21

 
                            ------------------------
 
   
    UNTIL DECEMBER 8, 1997 (25 DAYS AFTER THE DATE OF THIS PROSPECTUS), ALL
DEALERS EFFECTING TRANSACTIONS IN THE REGISTERED SECURITIES OFFERED HEREBY,
WHETHER OR NOT PARTICIPATING IN THIS DISTRIBUTION, MAY BE REQUIRED TO DELIVER A
PROSPECTUS. THIS IS IN ADDITION TO THE OBLIGATION OF DEALERS TO DELIVER A
PROSPECTUS WHEN ACTING AS UNDERWRITERS AND WITH RESPECT TO THEIR UNSOLD
ALLOTMENTS OR SUBSCRIPTIONS.
    
 
                                    ATLANTIC
                             PHARMACEUTICALS, INC.
 
                                 250,000 SHARES
                                  COMMON STOCK
 
                             ---------------------
 
                                   PROSPECTUS
 
                             ---------------------
 
   
                               NOVEMBER 12, 1997
    
 
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