Sec Form 3 Filing - SCHNELL DAVID @ INFINITY PHARMACEUTICALS, INC. - 2006-09-12

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person SCHNELL DAVID 2. Issuer Name and Ticker or Trading Symbol INFINITY PHARMACEUTICALS, INC. [ INFI] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O PROSPECT VENTURE PARTNERS, 435 TASSO STREET, SUITE 200 3. Date of Earliest Transaction (MM/DD/YY) 09/12/2006 (Street) PALO ALTO, CA94301 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 107,750 ( 1 ) ( 8 ) I By Prospect Venture Partners II, L.P. ( 2 ) Common Stock 510,575 ( 1 ) ( 9 ) I By Prospect Venture Partners II, L.P. ( 3 ) Common Stock 799,152 ( 1 ) ( 10 ) I By Prospect Venture Partners II, L.P. ( 4 ) Common Stock 107,750 ( 1 ) ( 11 ) I By Prospect Venture Partners, L.P. ( 5 ) Common Stock 510,575 ( 1 ) ( 12 ) I By Prospect Venture Partners, L.P. ( 6 ) Common Stock 66,596 ( 1 ) ( 13 ) I By Prospect Venture Partners, L.P. ( 7 ) Common Stock 26,938 ( 1 ) ( 14 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SCHNELL DAVID C/O PROSPECT VENTURE PARTNERS 435 TASSO STREET, SUITE 200 PALO ALTO, CA94301 X Signatures /s/ David Schnell 09/22/2006 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Reflects a 1:4 reverse stock split, which became effective September 12, 2006. ( 2 )The shares are owned by Prospect Venture Partners II, L.P. ("PVP II"). Prospect Management Co. II, L.L.C. ("PMC II") serves as the sole general partner of PVP II. James B. Tananbaum, M.D., Alexander E. Barkas, Ph.D., David Schnell, M.D., and Russell C. Hirsch, M.D., Ph.D. are the Managing Directors of PMC II. Each reporting person disclaims beneficial ownership of the shares reported herein, except to the extent of its pecuniary interest. Dr. Tananbaum, Dr. Barkas and Dr. Schnell have filed separate Section 16 reports relating to their holdings in the Issuer. ( 3 )The shares are owned by PVP II. ( 4 )The shares are owned by PVP II. ( 5 )The shares are owned by Prospect Venture Partners, L.P. ("PVP"). Prospect Management Co., L.L.C. ("PMC") serves as the sole general partner of PVP. Dr. Barkas and Dr. Schnell are the Managing Directors of PMC. Each reporting person disclaims beneficial ownership of the shares reported herein, except to the extent of its pecuniary interest. ( 6 )The shares are owned by PVP. ( 7 )The shares are owned by PVP. ( 8 )Received in exchange for 487,500 shares of Infinity Discovery, Inc. ("IPI") Common Stock in connection with the merger of IPI into Infinity Pharmaceuticals, Inc. (the "Merger") based on a conversion ratio of 0.88411. ( 9 )Received in exchange for 2,600,000 shares of IPI Series A Preferred Stock in connection with the Merger based on a conversion ratio of 0.78550. The Series A Preferred Stock had no expiration date. ( 10 )Received in exchange for 3,200,000 shares of IPI Series B Preferred Stock in connection with the Merger based on a conversion ratio of 0.99894. The Series B Preferred Stock had no expiration date. ( 11 )Received in exchange for 487,500 shares of IPI Common Stock in connection with the Merger based on a conversion ratio of 0.88411. ( 12 )Received in exchange for 2,600,000 shares of IPI Series A Preferred Stock in connection with the Merger based on a conversion ratio of 0.78550. The Series A Preferred Stock had no expiration date. ( 13 )Received in exchange for 266,667 shares of IPI Series B Preferred Stock in connection with the Merger based on a conversion ratio of 0.99894. The Series B Preferred Stock had no expiration date. ( 14 )Received in exchange for 121,875 shares of IPI Common Stock in connection with the Merger based on a conversion ratio of 0.88411.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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