SEC Form 3

FORM 3

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

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1. Name and Address of Reporting Person* PROSPECT VENTURE PARTNERS II LP (Last) (First) (Middle) C/O PROSPECT VENTURE PARTNERS 435 TASSO STREET, SUITE 200 (Street) PALO ALTO CA 94301 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 09/12/2006	3. Issuer Name and Ticker or Trading Symbol INFINITY PHARMACEUTICALS, INC. [ INFI ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
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)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

1. Name and Address of Reporting Person* PROSPECT VENTURE PARTNERS II LP (Last) (First) (Middle) C/O PROSPECT VENTURE PARTNERS 435 TASSO STREET, SUITE 200 (Street) PALO ALTO CA 94301 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* PROSPECT VENTURE PARTNERS LP (Last) (First) (Middle) C/O PROSPECT VENTURE PARTNERS 435 TASSO STREET, SUITE 200 (Street) PALO ALTO CA 94301 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* PROSPECT MANAGEMENT CO II LLC (Last) (First) (Middle) C/O PROSPECT VENTURE PARTNERS 435 TASSO STREET, SUITE 200 (Street) PALO ALTO CA 94301 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* PROSPECT MANAGEMENT CO LLC (Last) (First) (Middle) C/O PROSPECT VENTURE PARTNERS 435 TASSO STREET, SUITE 200 (Street) PALO ALTO CA 94301 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

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.

	/s/ David Schnell, Managing Director of Prospect Management Co. II, L.L.C.	09/22/2006
	/s/ David Schnell, Managing Director of Prospect Management Co., L.L.C.	09/22/2006
	/s/ David Schnell, Managing Director of Prospect Management Co. II, L.L.C., which serves as the sole general partner of Prospect Venture Partners II, L.P.	09/22/2006
	/s/ David Schnell, Managing Director of Prospect Management Co., L.L.C., which serves as the sole general partner of Prospect Venture Partners, L.P.	09/22/2006
	** Signature of Reporting Person	Date
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