**EXHIBIT      2.1**

*by      and between*

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**TABLE      OF CONTENTS**

| Article                  I                                                   | DEFINITIONS                  AND DEFINED TERMS                                                                     |                    1 |
|------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------|---------------------------|
|     Section                  1.1     |     Definitions                  and                  Defined Terms                            |                    1 |
| Article                  II                                                  | PURCHASE                  OF MEMBERSHIP INTEREST                                                                   |                    2 |
|     Section                  2.1                         |     Purchase                  and                  Sale of Membership Interest                 |                    2 |
|     Section                  2.2                         |     Purchase                  Price                                                            |                    2 |
|     Section                  2.3                         |     Allocation                  of                  Purchase Price                             |                    2 |
|     Section                  2.4                         |     Withholding                  Taxes                                                         |                    3 |
| Article                  III                                                 | CLOSING                                                                                                            |                    3 |
|     Section                  3.1                         |     Closing                                                                                    |                    3 |
|     Section                  3.2                         |     Deliveries                  at                  Closing                                    |                    3 |
| Article                  IV                                                  | REPRESENTATIONS                  AND WARRANTIES OF SELLER                                                          |                    5 |
|     Section                  4.1                         |     Ownership                  of                  Membership Interest; No Third Party Options |                    5 |
|     Section                  4.2                         |     Corporate                  Organization and Good Standing                                  |                    6 |
|     Section                  4.3                         |     Authorization                  and Effect of Agreement                                     |                    6 |
|     Section                  4.4                         |     Consents                  and                  Approvals; No Violations                    |                    6 |
|     Section                  4.5                         |     Litigation                                                                                 |                    7 |
|     Section                  4.6                         |     Performance                  of                  Obligations; Other Matters                |                    7 |
|     Section                  4.7                         |     Seller                  Sophistication; Excluded Information                               |                    7 |
|     Section                  4.8                         |     No                  Broker                                                                 |                    8 |
|     Section                  4.9                         |     No                  Misleading Statements                                                  |                    8 |
| Article                  V                                                   | REPRESENTATIONS                  AND WARRANTIES OF PURCHASER                                                       |                    8 |
|     Section                  5.1                         |     Corporate                  Organization and Good Standing                                  |                    8 |
|     Section                  5.2                         |     Authorization                  and Effect of Agreement                                     |                    9 |
|     Section                  5.3                         |     Consents                  and                  Approvals; No Violations                    |                    9 |
|     Section                  5.4                         |     No                  Broker                                                                 |                    9 |
|     Section                  5.5                         |     Litigation                                                                                 |                    9 |
|     Section                  5.6                         |     Performance                  of                  Obligations; Other Matters                | 10                        |
|     Section                  5.7                         |     No                  Misleading Statements                                                  | 10                        |

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|     Section                  5.8  |     Third                  Parties                                                                         | 10                         |
|-------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------|----------------------------|
| Article                  VI                           | COVENANTS                                                                                                                      | 10                         |
|     Section                  6.1  |     Further                  Assurances                                                                    | 10                         |
|     Section                  6.2  |     Confidentiality                                                                                        | 11                         |
|     Section                  6.3  |     Non-Hiring                                                                                             | 12                         |
|     Section                  6.4  |     Termination                  of                  Rights and Liabilities Under PSMA Operating Agreement | 12                         |
|     Section                  6.5  |     Tax                  Matters                                                                           | 13                         |
| Article                  VII                          | MISCELLANEOUS                  PROVISIONS                                                                                      | 14                         |
|     Section                  7.1  |     Notices                                                                                                | 14                         |
|     Section                  7.2  |     Expenses                                                                                               | 15                         |
|     Section                  7.3  |     Successors                  and                  Assigns                                               | 15                         |
|     Section                  7.4  |     Extension;                  Waiver                                                                     | 16                         |
|     Section                  7.5  |     Entire                  Agreement                                                                      | 16                         |
|     Section                  7.6  |     Amendments,                  Supplements, Etc                                                          | 16                         |
|     Section                  7.7  |     Applicable                  Law                                                                        | 16                         |
|     Section                  7.8  |     Execution                  in                  Counterparts                                            | 16     |
|     Section                  7.9  |     Titles                  and Headings                                                                   | 16                         |
|     Section                  7.10 |     Invalid                  Provisions                                                                    | 16                         |
|     Section                  7.11 |     Publicity                                                                                              | 16                         |
|     Section                  7.12 |     Specific                  Performance                                                                  | 17                         |

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**MEMBERSHIP      INTEREST PURCHASE AGREEMENT**

**RECITALS:**

**ARTICLE      I**

**DEFINITIONS      AND DEFINED TERMS**

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**    ARTICLE      II**

**PURCHASE      OF MEMBERSHIP INTEREST**

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**ARTICLE      III**

**CLOSING**

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**ARTICLE      IV**

**REPRESENTATIONS      AND WARRANTIES OF SELLER**

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**ARTICLE      V**

**REPRESENTATIONS      AND WARRANTIES OF PURCHASER**

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**ARTICLE      VI**

**COVENANTS**

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| (i)   | was                in the public domain or the subject of public knowledge at the time                of                disclosure; |
|-----------------|-------------------------------------------------------------------------------------------------------------------------------------|

| (ii)   | becomes                part of the public domain or the subject of public knowledge through                no                breach by or act of default of Seller;                or |
|------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (iii)   | is                obtained by Seller from a third party other than in breach of a legal                or                contractual obligation of confidentiality owed by such third party                to                Purchaser (or the Company) in respect thereof, the existence of which                such                obligation was known or should have been known by                Seller. |
|-------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

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**ARTICLE      VII**

**MISCELLANEOUS      PROVISIONS**

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**[**
**]**

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**PROGENICS      PHARMACEUTICALS, INC.**

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

**CYTOGEN      CORPORATION**

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| Term                                                                | Section                   |
|---------------------------------------------------------------------|---------------------------|
| Agents                                                              | 6.2(b)(iii)               |
| Agreement                                                           | Preamble                  |
| Amended                and Restated PSMA/PSMP License               | 3.2(a)(ii)                |
| Asset                Acquisition Statement                          | 2.3(a)                    |
| Claims                                                              | 6.4(c)                    |
| Closing                                                             | 3.1                       |
| Closing                Date                                         | 3.1                       |
| Company                                                        | Recitals                  |
| Confidential                Information                             | 6.2(a)                    |
| Disclosure                Schedule                                  | Article                IV |
| Management                Committee Waiver and Approval Certificate | 3.2(a)(v)                 |
| Managing                Representative Certificate                  | 3.2(a)(iv)                |
| Membership                Assignment                                | 3.2(a)(i)                 |
| Membership                Interest                             | 2.1                       |
| Proceedings                                                         | 4.5                       |
| PSMA                Operating Agreement                        | Recitals                  |
| Purchase                Price                                       | 2.2                       |
| Purchaser                                                           | Preamble                  |
| Resignations                                                        | 3.2(a)(iii)               |
| Reviewing                Accountants                                | 2.3(a)                    |
| Seller                                                              | Preamble                  |
| Tax                Matters Partner                                  | 6.5(a)                    |

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