UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Schedule 13G/A (Amendment No. 3) Under the Securities Exchange Act of 1934 Repligen Corp. -------------- Common Stock, par value $.01 per share (Title of Class of Securities) February 12, 2002 (CUSIP Number: 759916109) December 31, 2001 ----------------- Date of event which requires filing Check the appropriate box to designate the rule pursuant to which the schedule is filed: |_| Rule 13d-1(b) |X| Rule 13d-1(c) |_| Rule 13d-1(d) *The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page. The information required in the remainder of this cover page shall not be deemed to be filled for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act, but shall be subject to all other provisions of the Act (however, see the Notes to Schedule 13G). 1 CUSIP No. 759916109 13G Page 2 of 10 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Paramount Capital Asset Management, Inc. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |_| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware -------------------------------------------------------------------------------- 5 SOLE VOTING POWER None -------------------------------------------------------------- NUMBER OF 6 SHARED VOTING POWER SHARES BENEFICIALLY 2,380,650 OWNED BY -------------------------------------------------------------- EACH 7 SOLE DISPOSITIVE POWER REPORTING PERSON None WITH -------------------------------------------------------------- 8 SHARED DISPOSITIVE POWER 2,380,650 -------------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,380,650 -------------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 8.9% -------------------------------------------------------------------------------- 12 TYPE OF REPORTING PERSON* CO -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT 2 CUSIP No. 759916109 13G Page 3 of 10 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Aries Domestic Fund, L.P. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |_| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION Delaware -------------------------------------------------------------------------------- 5 SOLE VOTING POWER None -------------------------------------------------------------- NUMBER OF 6 SHARED VOTING POWER SHARES BENEFICIALLY 545,631 OWNED BY -------------------------------------------------------------- EACH 7 SOLE DISPOSITIVE POWER REPORTING PERSON None WITH -------------------------------------------------------------- 8 SHARED DISPOSITIVE POWER 545,631 -------------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 545,631 -------------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 2.0% -------------------------------------------------------------------------------- 12 TYPE OF REPORTING PERSON* PN -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT 3 CUSIP No. 759916109 13G Page 4 of 10 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON The Aries Master Fund II -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |_| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION Cayman Islands -------------------------------------------------------------------------------- 5 SOLE VOTING POWER None -------------------------------------------------------------- NUMBER OF 6 SHARED VOTING POWER SHARES BENEFICIALLY 1,835,019 OWNED BY -------------------------------------------------------------- EACH 7 SOLE DISPOSITIVE POWER REPORTING PERSON None WITH -------------------------------------------------------------- 8 SHARED DISPOSITIVE POWER 1,835,019 -------------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,835,019 -------------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.4% -------------------------------------------------------------------------------- 12 TYPE OF REPORTING PERSON* OO (see Item 2) -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT 4 CUSIP No. 759916109 13G Page 5 of 10 -------------------------------------------------------------------------------- 1 NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Lindsay A. Rosenwald, M.D. -------------------------------------------------------------------------------- 2 CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a) |_| (b) |_| -------------------------------------------------------------------------------- 3 SEC USE ONLY -------------------------------------------------------------------------------- 4 CITIZENSHIP OR PLACE OF ORGANIZATION United States -------------------------------------------------------------------------------- 5 SOLE VOTING POWER 33,250 -------------------------------------------------------------- NUMBER OF 6 SHARED VOTING POWER SHARES BENEFICIALLY 2,380,650 OWNED BY -------------------------------------------------------------- EACH 7 SOLE DISPOSITIVE POWER REPORTING PERSON 33,250 WITH -------------------------------------------------------------- 8 SHARED DISPOSITIVE POWER 2,380,650 -------------------------------------------------------------------------------- 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,413,900 -------------------------------------------------------------------------------- 10 CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES* |_| -------------------------------------------------------------------------------- 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 9.1% -------------------------------------------------------------------------------- 12 TYPE OF REPORTING PERSON* IN -------------------------------------------------------------------------------- *SEE INSTRUCTIONS BEFORE FILLING OUT 5 ITEM 1(a). NAME OF ISSUER: Repligen Corporation. ITEM 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES: 117 Fourth Avenue, Needham, MA 02494 ITEM 2(a) NAME OF PERSON FILING: This statement is filed on behalf of Paramount Capital Asset Management, Inc. ("Paramount Capital"), Aries Domestic Fund, L.P. ("Aries Domestic"), Aries Master Fund II, a Cayman Island exempted company ("Aries Fund") and Lindsay A. Rosenwald, M.D. ("Dr. Rosenwald" and collectively, "Reporting Parties"). See attached Exhibit A which is a copy of their agreement in writing to file this statement on behalf of each of them. Dr. Rosenwald is an investment banker, venture capitalist, fund manager and sole stockholder of Paramount Capital,1 a Subchapter S corporation incorporated in Delaware. Paramount Capital is the General Partner to each of Aries Domestic,2 and Aries Domestic II, limited partnerships incorporated in Delaware. Paramount Capital is the Investment Manager to Aries Fund,3 a Cayman Islands exempted company. Dr. Rosenwald, Paramount Capital, Aries Domestic and Aries Fund and their respective officers, directors, general partners, investment managers, or trustees have not, during the five years prior to the date hereof, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). ITEM 2(b) ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE: Paramount Capital's, Aries Domestic's, and Dr. Rosenwald's business address is 787 Seventh Avenue, 48th Floor, New York, New York, 10019. The business address for The Aries Fund is c/o Fortis Fund Services Cayman Limited, Grand Pavilion Commercial Center, 802 West Bay Road, Grand Cayman, Cayman Islands. ITEM 2(c). CITIZENSHIP: Dr. Rosenwald is a citizen of the United States of America. ITEM 2(d). TITLE OF CLASS OF SECURITIES: Common Stock, par value $0.01 per share. ---------- (1) Please see attached Exhibit B indicating the executive officers and directors of Paramount Capital and providing information called for by Items 2-6 of this statement as to said officers and directors. Exhibit B is herein incorporated by reference. (2) Please see attached Exhibit C indicating the general partner to each of Aries Domestic and Aries II and the general partner's executive officers and directors and providing information called for by Items 2-6 of this statement as to said general partners, officers and directors. Exhibit C is herein incorporated by reference. (3) Please see attached Exhibit D indicating the investment manager of the Aries Fund and the investment manager's executive officers and directors and providing information called for by Items 2-6 of this statement as to said investment manager and officers and directors. Exhibit D is herein incorporated by reference. 6 ITEM 2(e). CUSIP NUMBER: 759916109 ITEM 3. |X| CHECK THIS BOX IF THIS STATEMENT IS FILED PURSUANT TO RULE 13d-1(c) ITEM 4. OWNERSHIP For information concerning the ownership of Common Stock of the Company by the Reporting Persons, see Items 5 through 9 and 11 of the cover pages to this schedule 13G and footnotes thereto. ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS Not applicable ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON Not applicable ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY Not Applicable ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP Not Applicable ITEM 9. NOTICE OF DISSOLUTION OF GROUP Not Applicable ITEM 10. CERTIFICATION By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in a transaction having that purpose and effect. Material to be Filed as Exhibits: Exhibit A - Copy of an Agreement between Dr. Rosenwald, Paramount Capital, Aries Domestic, Aries II and Aries Fund to file this Statement on Schedule 13G on behalf of each of them. Exhibit B - List of executive officers and directors of Paramount Capital and information called for by Items 2-6 of this statement relating to said officers and directors. Exhibit C - List of executive officers and directors of Aries Domestic and Aries II and information called for by Items 2-6 of this statement relating to said officers and directors. Exhibit D - List of executive officers and directors of Aries Fund and information called for by Items 2-6 of this statement relating to said officers and directors. 7 SIGNATURES After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. PARAMOUNT CAPITAL ASSET MANAGEMENT, INC. Dated: February 12, 2002 By /s/ Lindsay A. Rosenwald, M.D. New York, NY ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman ARIES DOMESTIC FUND, L.P. By Paramount Capital Asset Management, Inc., General Partner Dated: February 12, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman THE ARIES MASTER FUND II By Paramount Capital Asset Management, Inc. Investment Manager Dated: February 12, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman Dated: February 12, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. 8 EXHIBIT A AGREEMENT JOINT FILING OF SCHEDULE 13G The undersigned hereby agrees to jointly prepare and file with regulatory authorities a Schedule 13G and any future amendments thereto reporting each of the undersigned's ownership of securities of Repligen Corp.and hereby affirm that such Schedule 13G is being filed on behalf of each of the undersigned. PARAMOUNT CAPITAL ASSET MANAGEMENT, INC. Dated: February 10, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman ARIES DOMESTIC FUND, L.P. By Paramount Capital Asset Management, Inc., General Partner Dated: February 10, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman THE ARIES DOMESTIC FUND II, L.P. By Paramount Capital Asset Management, Inc. General Partner Dated: February 10, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman THE ARIES MASTER FUND II By Paramount Capital Asset Management, Inc. Investment Manager Dated: February 10, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. Title: Chairman Dated: February 10, 2002 New York, NY By /s/ Lindsay A. Rosenwald, M.D. ----------------------------------------- Name: Lindsay A. Rosenwald, M.D. 9 EXHIBIT B The name and principal occupation or employment, which in each instance is with Paramount Capital Asset Management, Inc. ("Paramount Capital") located at 787 Seventh Avenue, 48th Floor, New York, New York, 10019, of each executive officer and director of Paramount Capital is as follows: NAME PRINCIPAL OCCUPATION ---- OR EMPLOYMENT ------------- Lindsay A. Rosenwald, M.D. Chairman of the Board and sole shareholder, Paramount Capital Asset Management, Inc., Paramount Capital Investments LLC and Paramount Capital, Inc. Mark C. Rogers, M.D. President of Paramount Capital Asset Management, Inc., Paramount Capital Investments, LLC, and Paramount Capital, Inc. Peter Morgan Kash Director of Paramount Capital Asset Management, Inc., Senior Managing Director, Paramount Capital, Inc. Dr. Yuichi Iwaki Director of Paramount Capital Asset Management, Inc., Professor, University of Southern California School of Medicine Item 2. During the five years prior to the date hereof, the above person (to the best of Paramount Capital's knowledge) has not been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). Additionally, during the five years prior to the date hereof, the above person (to the best of Paramount Capital's knowledge) has not been a party to a civil proceeding, of a judicial or administrative body of competent jurisdiction, as a result of which such person was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, Federal or State securities laws or finding any violation with respect to such laws. Items 3-6. Please refer to Items 3-6 herein reporting the beneficial ownership. 10 EXHIBIT C The name and principal occupation or employment of the General Partner of Aries Domestic and Aries II, which are located at 787 Seventh Avenue, 48th Floor, New York, New York, 10019, is as follows: NAME PRINCIPAL OCCUPATION ---- OR EMPLOYMENT ------------- Paramount Capital Asset Management, Inc General Partner; Investment Manager Exhibit B is hereby incorporated by reference. Item 2. During the five years prior to the date hereof, the above person (to the best of Aries Domestic's and Aries II's knowledge) has not been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). Additionally, during the five years prior to the date hereof, the above person (to the best of Aries Domestic's and Aries II's knowledge) has not been a party to a civil proceeding, of a judicial or administrative body of competent jurisdiction, as a result of which such person was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, Federal or State securities laws or finding any violation with respect to such laws. Items 3-6. Please refer to Items 3-6 herein reporting the beneficial ownership. 11 EXHIBIT D The name and principal occupation or employment, which in the case of Paramount Capital Asset Management, Inc. is located at 787 Seventh Avenue, 48th Floor, New York, New York, 10019, of each executive officer and director of Aries Fund is as follows: PRINCIPAL OCCUPATION NAME OR EMPLOYMENT ---- ------------- Paramount Capital Asset Management, Inc. Investment Manager Fortis Fund Services Cayman Limited Administrator Grand Pavilion Commercial Center 802 West Bay Road Grand Cayman, Cayman Islands Exhibit B is hereby incorporated by reference. Item 2. During the five years prior to the date hereof, the above person (to the best of Aries Fund's knowledge) has not been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). Additionally, during the five years prior to the date hereof, the above person (to the best of Aries Fund's knowledge) has not been a party to a civil proceeding, of a judicial or administrative body of competent jurisdiction, as a result of which such person was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, Federal or State securities laws or finding any violation with respect to such laws. Items 3-6. Please refer to Items 3-6 herein reporting the beneficial ownership. 12