EXHIBIT 2.1


                                                                  EXECUTION COPY



                              AMENDMENT NUMBER 1 TO
             PURCHASE AGREEMENT, CONTRACT SALES FORCE AGREEMENT AND
                           CONFIDENTIALITY AGREEMENT


         THIS AMENDMENT, (the "AMENDMENT") effective as of November 30, 2006
(the "EFFECTIVE DATE OF THIS AMENDMENT"), is made by and between LIGAND
PHARMACEUTICALS INCORPORATED, a Delaware corporation, and all of its successors
and assigns (the "SELLER"), KING PHARMACEUTICALS, INC., a Tennessee corporation
("KING") and KING PHARMACEUTICALS RESEARCH AND DEVELOPMENT, INC., a Delaware
corporation and wholly owned subsidiary of King ("KING R & D; King R & D
together with King, the "PURCHASER"). Each of Seller and Purchaser is referred
to herein, individually, as a "PARTY" and, collectively, as the "Parties."

         WHEREAS, the Seller and Purchaser entered into that certain Purchase
Agreement, dated as of September 6, 2006 (the "PURCHASE AGREEMENT");

         WHEREAS, the Seller and King entered into that certain Contract Sales
Force Agreement, dated as of September 6, 2006 (the "SALES FORCE AGREEMENT");

         WHEREAS, the Seller and King entered into that certain Confidentiality
Agreement dated as of August 15, 2006 (the "CONFIDENTIALITY AGREEMENT")
(together with the Purchase Agreement, and the Sales Force Agreement, the
"AGREEMENTS");

         WHEREAS, the Seller and Purchaser desire to amend the Purchase
Agreement, as described in this Amendment; and

         WHEREAS, the Seller and King desire to amend each of the Sales Force
Agreement and the Confidentiality Agreement, as described in this Amendment.

         NOW, THEREFORE, the Parties hereby agree as follows:

         1. The terms in this Amendment with initial letters capitalized shall
have the meanings set forth in this Amendment and, if not defined in this
Amendment, shall have the meaning set forth in the applicable Agreement.

         2. SECTION 9.1(A) of the Purchase Agreement is hereby amended to insert
the following prior to the final sentence:

                  "Effective as of November 30, 2006, Purchaser may make offers
                  of employment to any of the Seller's Regional Business
                  Managers (the "RBMS") and such other of the Seller employees
                  as Purchaser shall require and as the Seller shall from time
                  to time agree (the "OTHER EMPLOYEES"), which offers shall be
                  contingent upon the Closing. The RBMs and Other Employees
                  shall not be counted for purposes of calculating severance
                  reimbursement to the Seller under SECTION 9.1(C) hereof. The
                  Seller shall permit all employees receiving offers under this
                  Agreement to attend Purchaser's sales/training meetings as
                  Purchaser may specify and as the Seller may from time to time
                  agree, at Purchaser's expense."

         3. The final sentence of SECTION 9.1(A) shall be amended to read as
follows:



                  "The Product Employees, RBMs and Other Employees who become
                  employed by Purchaser are herein referred to as the "HIRED
                  EMPLOYEES"."

         4. SECTION 9.1(B) of the Purchase Agreement is hereby amended to insert
the following after the final sentence:

                  "Seller shall be responsible for a pro-rata portion of any
                  sales incentive bonus earned by its employees per its bonus
                  plans up to the date of termination from Seller's employ.
                  Purchaser shall thereafter be responsible to compensate all
                  Product Employees who become employed by Purchaser in
                  accordance with Purchaser's compensation policies."

         5. The first sentence of SECTION 9.1(C) of the Purchase Agreement shall
be amended to read as follows:

                  "All Product Employees on SCHEDULE 9.1(A)(1) or RBMs who do
                  not receive an employment offer from Purchaser as of December
                  6, 2006, may, at Seller's sole option, remain employees of
                  Seller or be terminated from Seller's employment at any time
                  after December 14, 2006."

         6. SCHEDULE 9.1(A)(2) of the Purchase Agreement shall be amended to
read as follows:

                  "In exchange for a release of claims in accordance with
                  paragraph 9.2(c), each Product Employee not offered employment
                  by Purchaser, will be offered severance as follows: Each
                  severed Product Employee shall receive two (2) months regular
                  salary plus one (1) week salary for each year of service. For
                  clarity, a year of service shall be deemed to accrue on the
                  one hundred eighty third (183rd) day after the relevant start
                  date anniversary."

         7. SECTION 11.1(A)(II) of the Purchase Agreement shall be amended to
replace "December 31, 2006" with "February 28, 2007" as the "Outside Date" of
the Purchase Agreement.

         8. SECTION 12.3 of the Sales Force Agreement shall be amended to
replace "thirty (30) days" with "sixty (60) days".

         9. PARAGRAPH 1 of the Confidentiality Agreement shall be amended to add
the following final sentence:

                  "Upon Closing (as such term is defined in that certain
                  Purchase Agreement by and among Ligand Pharmaceuticals
                  Incorporated, King Pharmaceuticals, Inc. and King
                  Pharmaceuticals Research and Development, Inc. and dated as of
                  September 6, 2006 (the "PURCHASE AGREEMENT"), Proprietary
                  Information of King received by Ligand as the Receiving Party
                  hereunder shall also be deemed to include all Product Records
                  (again, as such term is defined in the Purchase Agreement),
                  and the exception to the confidentiality obligations set forth
                  below in Paragraph 2(b) shall not apply to such Product
                  Records."



         10. This Amendment shall not amend or modify the covenants, terms,
conditions, rights and obligations of the Parties under the Agreements, except
as specifically set forth herein. The Agreements shall continue in full force
and effect in accordance with their terms as amended by this Amendment.


                                                  * * *


                            [signature page follows]









         IN WITNESS WHEREOF, the Parties have executed this Amendment in
multiple counterparts.


LIGAND PHARMACEUTICALS                       KING PHARMACEUTICALS, INC.
INCORPORATED

By:  /s/ Warner R. Broaddus                  By: /s/ James W. Elrod
    --------------------------------             -------------------------------

Title: Vice President, General Counsel       Title: General Counsel
       & Secretary                                  & Secretary
       -------------------------------         ---------------------------------


KING PHARMACEUTICALS RESEARCH
AND DEVELOPMENT, INC.

By:  /s/ James W. Elrod
    ------------------------

Title: Secretary
       ---------------------