SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
Schedule 13G
(Rule 13d-102)
 
INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1 (b), (c) AND (d)
AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b)
(Amendment No. ___________)*

 
Zafgen, Inc.
 (Name of Issuer)

Common Stock
(Title of Class of Securities)

	98885E103	
(CUSIP Number)

October 14, 2015
(Date of Event Which Requires Filing of this Statement)
 
Check the appropriate box to designate the rule pursuant to which this 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 on the remainder of this cover page shall not be deemed to be “filed” 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).
 
(Continued on following pages)

Page 1 of 11
 
Exhibit Index on Page 10

 
CUSIP # 98885E103	 	Page 2 of 11	

1	NAME OF REPORTING PERSONS	          Foresite Capital Fund II, L.P. (“FCF II”)	 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a)     ¨     (b)     x	 	
3	SEC USE ONLY	 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	 	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY EACH
REPORTING
PERSON
WITH	5	SOLE VOTING POWER
1,098,800 shares, except that Foresite Capital Management II, LLC (“FCM II”), the general partner of FCF II, may be deemed to have sole power to vote these shares, and James Tananbaum (“Tananbaum”), the managing member of FCM II, may be deemed to have sole power to vote these shares.	 	
 	6	SHARED VOTING POWER
See response to row 5.	 	 	 	
 	7	SOLE DISPOSITIVE POWER
1,098,800 shares, except that FCM II, the general partner of FCF II, may be deemed to have sole power to dispose of these shares, and Tananbaum, the managing member of FCM II, may be deemed to have sole power to dispose of these shares.
 	 	 	 	 	 	
 	8	SHARED DISPOSITIVE POWER
See response to row 7.	 	 	 	 	 	 	
 	 	 	 	 	 	 	 	 	 	
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	1,098,800	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	[_]	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	4.05%	
12	TYPE OF REPORTING PERSON	PN	

CUSIP # 98885E103	 	Page 3 of 11	

1	NAME OF REPORTING PERSONS	          Foresite Capital Management II, LLC (“FCM II”)	 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a)     ¨     (b)     x	 	
3	SEC USE ONLY	 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	 	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY EACH
REPORTING
PERSON
WITH	5	SOLE VOTING POWER
1,098,800 shares, all of which are directly owned by Foresite Capital Fund II, L.P. (“FCF II”).  FCM II, the general partner of FCF II, may be deemed to have sole power to vote these shares, and James Tananbaum (“Tananbaum”), the managing member of FCM II, may be deemed to have sole power to vote these shares.	 	
 	6	SHARED VOTING POWER
See response to row 5.	 	 	 	
 	7	SOLE DISPOSITIVE POWER
1,098,800 shares, all of which are directly owned by FCF II.  FCM II, the general partner of FCF II, may be deemed to have sole power to dispose of these shares, and Tananbaum, the managing member of FCM II, may be deemed to have sole power to dispose of these shares.	 	 	 	 	 	
 	8	SHARED DISPOSITIVE POWER
See response to row 7.	 	 	 	 	 	 	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	1,098,800	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	4.05%	
12	TYPE OF REPORTING PERSON	OO	

CUSIP # 98885E103	 	Page 4 of 11	

1	NAME OF REPORTING PERSONS	          Foresite Capital Fund III, L.P. (“FCF III”)	 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a)     ¨     (b)     x	 	
3	SEC USE ONLY	 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	 	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY EACH
REPORTING
PERSON
WITH	5	SOLE VOTING POWER
388,500 shares, except that Foresite Capital Management III, LLC (“FCM III”), the general partner of FCF III, may be deemed to have sole power to vote these shares, and James Tananbaum (“Tananbaum”), the managing member of FCM III, may be deemed to have sole power to vote these shares.	 	
 	6	SHARED VOTING POWER
See response to row 5.	 	 	 	
 	7	SOLE DISPOSITIVE POWER
388,500 shares, except that FCM III, the general partner of FCF III, may be deemed to have sole power to dispose of these shares, and Tananbaum, the managing member of FCM III, may be deemed to have sole power to dispose of these shares.	 	 	 	 	 	
 	8	SHARED DISPOSITIVE POWER
See response to row 7.	 	 	 	 	 	 	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	388,500	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES		¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	1.43%	
12	TYPE OF REPORTING PERSON	PN	

CUSIP # 98885E103	 	Page 5 of 11	

1	NAME OF REPORTING PERSONS	          Foresite Capital Management III, LLC (“FCM III”)	 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a)     ¨     (b)     x	 	
3	SEC USE ONLY	 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware	 	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY EACH
REPORTING
PERSON
WITH	5	SOLE VOTING POWER
388,500 shares, all of which are directly owned by Foresite Capital Fund III, L.P. (“FCF III”).  FCM III, the general partner of FCF III, may be deemed to have sole power to vote these shares, and James Tananbaum (“Tananbaum”), the managing member of FCM III, may be deemed to have sole power to vote these shares.	 	
 	6	SHARED VOTING POWER
See response to row 5.	 	 	 	
 	7	SOLE DISPOSITIVE POWER
388,500 shares, all of which are directly owned by FCF III.  FCM III, the general partner of FCF III, may be deemed to have sole power to dispose of these shares, and Tananbaum, the managing member of FCM III, may be deemed to have sole power to dispose of these shares.	 	 	 	 	 	
 	8	SHARED DISPOSITIVE POWER
See response to row 7.	 	 	 	 	 	 	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH  REPORTING PERSON	388,500	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES		¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9	1.43%	
12	TYPE OF REPORTING PERSON	OO	

CUSIP # 98885E103	 	Page 6 of 11	

1	NAME OF REPORTING PERSONS	          James Tananbaum (“Tananbaum”)	 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a)     ¨     (b)     x	 	
3	SEC USE ONLY	 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
United States	 	
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY EACH
REPORTING
PERSON
WITH	5	SOLE VOTING POWER
1,487,300 shares, of which 1,098,800 shares are directly owned by Foresite Capital Fund II, L.P. (“FCF II”), and 388,500 shares are directly owned by Foresite Capital Fund III, L.P. (“FCF III”).  Tananbaum is the managing member of each of Foresite Capital Management II, LLC (“FCM II”), which is the general partner of FCF II, and Foresite Capital Management III, LLC (“FCM III”), which is the general partner of FCF III.  Tananbaum may be deemed to have sole power to vote these shares.	 	
 	6	SHARED VOTING POWER
See response to row 5.	 	 	 	
 	7	SOLE DISPOSITIVE POWER
1,487,300 shares, of which 1,098,800 shares are directly owned by FCF II, and 388,500 shares are directly owned by FCF III.  Tananbaum is the managing member of each FCM II, which is the general partner of FCF II, and FCM III, which is the general partner of FCF III.  Tananbaum may be deemed to have sole power to dispose of these shares.	 	 	 	 	 	
 	8	SHARED DISPOSITIVE POWER
See response to row 7.	 	 	 	 	 	 	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON	1,487,300	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES	¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9  	5.48%	
12	TYPE OF REPORTING PERSON	IN	

CUSIP # 98885E103	 	Page 7 of 11	

ITEM 1(A).	NAME OF ISSUER	
 	Zafgen, Inc. (the “Issuer”)	

ITEM 1(B).	ADDRESS OF ISSUER’S PRINCIPAL EXECUTIVE OFFICES	
 	 	
 	175 Portland Street, 4th Floor	
 	Boston, Massachusetts 02114	

ITEM 2(A).	NAME OF PERSONS FILING	
 	This Schedule is filed by Foresite Capital Fund II, L.P., a Delaware limited partnership, Foresite Capital Management II, LLC, a Delaware limited liability company, Foresite Capital Fund III, L.P., a Delaware limited partnership, Foresite Capital Management III, LLC, a Delaware limited liability company and James Tananbaum.The foregoing entities and individuals are collectively referred to as the “Reporting Persons.”	
ITEM 2(B).	ADDRESS OF PRINCIPAL OFFICE	
 	The address for each of the Reporting Persons is:	

 	c/o Foresite Capital Management	
 	101 California Street, Suite 4100	
 	San Francisco, CA 94111	

ITEM 2(C).	CITIZENSHIP	
 	See Row 4 of cover page for each Reporting Person.	
ITEM 2(D).	TITLE OF CLASS OF SECURITIES	
 	Common Stock	
ITEM 2(E)	CUSIP NUMBER	
 	98885E103	
ITEM 3.	If this statement is filed pursuant to Rule 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:	
 	Not applicable.	
ITEM 4.	OWNERSHIP	
 	The following information with respect to the ownership of the common stock of the Issuer by the persons filing this Statement is provided as of October 22, 2015:	

 	(a)	Amount beneficially owned:	
 	 	See Row 9 of cover page for each Reporting Person.	
 	(b)	Percent of Class:	
 	 	See Row 11 of cover page for each Reporting Person.	

 
CUSIP # 98885E103	 	Page 8 of 11	

 	(c)	Number of shares as to which such person has:	

 	(i)	Sole power to vote or to direct the vote:	
 	 	 	
 	 	See Row 5 of cover page for each Reporting Person.	
 	 	 	
 	(ii)	Shared power to vote or to direct the vote:	
 	 	 	
 	 	See Row 6 of cover page for each Reporting Person.	
 	 	 	
 	(iii)	Sole power to dispose or to direct the disposition of:	
 	 	 	
 	 	See Row 7 of cover page for each Reporting Person.	
 	 	 	
 	(iv)	Shared power to dispose or to direct the disposition of:	
 	 	 	
 	 	See Row 8 of cover page for each Reporting Person.	

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.	
 	Under certain circumstances set forth in the limited partnership agreements of FCF II and FCF III and the limited liability company agreements of FCM II and FCM III the partners or members, as the case may be, of each of such entities may be deemed to have the right to receive dividends from, or the proceeds from the sale of, shares of the Issuer directly or indirectly owned by each such entity of which they are a partner or member.	
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 any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.	

CUSIP # 98885E103	 	Page 9 of 11	

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.
 
Date: October 22, 2015	

 	FORESITE CAPITAL FUND II, L.P.	

 	By:	FORESITE CAPITAL MANAGEMENT II, LLC	
 	Its:	General Partner	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	FORESITE CAPITAL MANAGEMENT II, LLC	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	FORESITE CAPITAL FUND III, L.P.	

 	By:	FORESITE CAPITAL MANAGEMENT III, LLC	
 	Its:	General Partner	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	FORESITE CAPITAL MANAGEMENT III, LLC	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	JAMES TANANBAUM	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	

CUSIP # 98885E103	 	Page 10 of 11	

EXHIBIT INDEX
 	Found on
Sequentially	
Exhibit	Numbered Page	
 	 	
Exhibit A:   Agreement of Joint Filing	11	

 	 	

CUSIP # 98885E103	 	Page 11 of 11	

exhibit A
 
Agreement of Joint Filing
 
The undersigned hereby agree that a single Schedule 13G (or any amendment thereto) relating to the common stock of the Issuer shall be filed on behalf of each of the undersigned and that this Agreement shall be filed as an exhibit to such Schedule 13G.
 
Date: October 22, 2015	

 	

 	FORESITE CAPITAL FUND II, L.P.	

 	By:	FORESITE CAPITAL MANAGEMENT II, LLC	
 	Its:	General Partner	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	FORESITE CAPITAL MANAGEMENT II, LLC	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	FORESITE CAPITAL FUND III, L.P.	

 	By:	FORESITE CAPITAL MANAGEMENT III, LLC	
 	Its:	General Partner	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	FORESITE CAPITAL MANAGEMENT III, LLC	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum	
 	Title:	Managing Member	

 	 	 	
 	 	 	
 	JAMES TANANBAUM	

 	By:	/s/ James Tananbaum	
 	Name:	James Tananbaum