UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934¹

Optimer Pharmaceuticals, Inc.

(Name of Issuer)

Common Stock, no par value

(Title of Class of Securities)

68401H104

(CUSIP Number)

December 31, 2007

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

o Rule 13d-1(b)

x Rule 13d-1(c)

o Rule 13d-1(d)

_______________

¹ 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 the disclosures provided in a prior cover page.

The information required in 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 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).

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1.	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY) ProQuest Investments II, L.P. 22-3764772
2.	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP**			(a) o (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 -0-
		6.	SHARED VOTING POWER 1,275,357
		7.	SOLE DISPOSITIVE POWER -0-
		8.	SHARED DISPOSITIVE POWER 1,275,357
9.	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,275,357
10.	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES CERTAIN SHARES** o
11.	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 6.0%
12.	TYPE OF REPORTING PERSON** PN
	** SEE INSTRUCTIONS BEFORE FILLING OUT

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1.	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY) ProQuest Investments II Advisors Fund, L.P. 22-3784567
2.	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP**			(a) o (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 -0-
		6.	SHARED VOTING POWER 54,106
		7.	SOLE DISPOSITIVE POWER -0-
		8.	SHARED DISPOSITIVE POWER 54,106
9.	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 54,106
10.	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES CERTAIN SHARES** o
11.	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.3%
12.	TYPE OF REPORTING PERSON** OO
	** SEE INSTRUCTIONS BEFORE FILLING OUT

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1.	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY) ProQuest Associates II, LLC 22-3764735
2.	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP**			(a) o (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 -0-
		6.	SHARED VOTING POWER 1,329,463
		7.	SOLE DISPOSITIVE POWER -0-
		8.	SHARED DISPOSITIVE POWER 1,329,463
9.	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,329,463
10.	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES CERTAIN SHARES** o
11.	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 6.3%
12.	TYPE OF REPORTING PERSON** PN
	** SEE INSTRUCTIONS BEFORE FILLING OUT

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1.	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY) ProQuest Management LLC 04-3428179
2.	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP**			(a) o (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 -0-
		6.	SHARED VOTING POWER 2,500
		7.	SOLE DISPOSITIVE POWER -0-
		8.	SHARED DISPOSITIVE POWER 2,500
9.	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,500
10.	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES CERTAIN SHARES** o
11.	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 0.1%
12.	TYPE OF REPORTING PERSON** OO
	** SEE INSTRUCTIONS BEFORE FILLING OUT

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1.	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY) Jay Moorin
2.	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP**			(a) o (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 -0-
		6.	SHARED VOTING POWER 1,331,963
		7.	SOLE DISPOSITIVE POWER -0-
		8.	SHARED DISPOSITIVE POWER 1,331,963
9.	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,331,963
10.	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES CERTAIN SHARES** o
11.	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 6.3%
12.	TYPE OF REPORTING PERSON** IN
	** SEE INSTRUCTIONS BEFORE FILLING OUT

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1.	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY) Alain Schreiber
2.	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP**			(a) o (b) x
3.	SEC USE ONLY
4.	CITIZENSHIP OR PLACE OF ORGANIZATION United States Resident Alien
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		5.	SOLE VOTING POWER 119,226*
		6.	SHARED VOTING POWER 1,331,963
		7.	SOLE DISPOSITIVE POWER 119,226*
		8.	SHARED DISPOSITIVE POWER 1,331,963
9.	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,451,189*
10.	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES CERTAIN SHARES** o
11.	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9 6.8%
12.	TYPE OF REPORTING PERSON** IN
	** SEE INSTRUCTIONS BEFORE FILLING OUT

*Includes 114,226 shares subject to currently exercisable options and 5,000 shares subject to options that vest 1/12 per month commencing 1/1/08.

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Item 1(a).

Name of Issuer.

Optimer Pharmaceuticals, Inc. (the “Company”).

Item 1(b).

Address of Issuer’s Principal Executive Offices.

The Company’s principal executive offices are located at 10110 Sorrento Valley Road, Suite C, San Diego, California 92121.

Items 2(a).

Name of Person Filing.

This statement is filed on behalf of the following persons with respect to shares of common stock of the Company and shares subject to options to purchase shares of common stock of the Company acquired by such persons (collectively, the “Shares”):

(i) ProQuest Investments II, L.P., a Delaware limited partnership (“Investments III”), with respect to Shares beneficially owned by it;

(ii) ProQuest Investments II Advisors Fund, L.P., a Delaware limited partnership (“Advisors Fund”), with respect to Shares beneficially owned by it;

(iii) ProQuest Associates II LLC, a Delaware limited liability company (“Associates III”), as General Partner of Investments II and Advisors Fund, with respect to Shares beneficially owned by Investments II and Advisors Fund;

(iv) ProQuest Management, LLC, a Delaware limited liability company (“Management”), with respect to Shares beneficially owned by it;

(v) Jay Moorin, an individual and a member of Associates II and Management (“Moorin”), with respect to Shares beneficially owned by Investments II and Management; and

(vi) Alain Schreiber, an individual and a member of Associates II and Management (“Schreiber”), with respect to Shares beneficially owned by Investments II and Management and by him.

The foregoing persons are hereinafter are referred to collectively as the “Reporting Persons.” Any disclosures herein with respect to persons other than the Reporting Persons are made on information and belief after making inquiry to the appropriate party.

Item 2(b).

Address of Principal Business Office or, if None, Residence.

The address of the principal business office of each of the Reporting Persons is 90 Nassau Street, 5^th Floor, Princeton, NJ 08542.

Item 2(c).

Citizenship.

Mr. Moorin is a United States citizen. Mr. Schreiber is a United States resident alien. Investments II and Advisors Fund are Delaware limited partnerships organized under the laws of

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the State of Delaware. Associates II and Management are Delaware limited liability companies organized under the laws of the State of Delaware.

Item 2(d).

Title of Class of Securities.

Common stock, no par value.

Item 2(e).

CUSIP Number.

68401H104

Item 3.

If this statement is filed pursuant to Rules 13d-1(b) or 13d- 2(b) or (c), check whether the person filing is a:

(a)	o	Broker or dealer registered under Section 15 of the Act,
(b)	o	Bank as defined in Section 3(a)(6) of the Act,
(c)	o	Insurance Company as defined in Section 3(a)(19) of the Act,
(d)	o	Investment Company registered under Section 8 of the Investment Company Act of 1940,
(e)	o	Investment Adviser in accordance with Rule 13d-1 (b)(1)(ii)(E),
(f)	o	Employee Benefit Plan or Endowment Fund in accordance with 13d-1 (b)(1)(ii)(F),
(g)	o	Parent Holding Company or control person in accordance with Rule 13d-1 (b)(1)(ii)(G),
(h)	o	Savings Association as defined in Section 3(b) of the Federal Deposit Insurance Act,
(i)	o	Church Plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act of 1940,
(j)	o	Group, in accordance with Rule 13d-1(b)(1)(ii)(J).

Item 4.

Ownership.

The percentages used herein are calculated based upon 21,220,614 shares issued and outstanding, as of November 2, 2007, based upon the Company’s Quarterly Report on Form 10-for the quarter ended September 30, 2007. As of the close of business on December 31, 2007, the Reporting Persons beneficially owned shares of the Company’s common stock in the amounts and percentages listed below:

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A.	ProQuest Investments II, L.P.
(a)	Amount beneficially owned: 1,275,357
(b)	Percent of class: 6.0%
(c)	(i)	Sole power to vote or direct the vote: -0-
	(ii)	Shared power to vote or direct the vote: 1,275,357
	(iii)	Sole power to dispose or direct the disposition: -0-
	(iv)	Shared power to dispose or direct the disposition: 1,275,357
B.	ProQuest Investments II Advisors Fund, L.P.
(a)	Amount beneficially owned: 54,106
(b)	Percent of class: 0.3%
(c)	(i)	Sole power to vote or direct the vote: -0-
	(ii)	Shared power to vote or direct the vote: 54,106
	(iii)	Sole power to dispose or direct the disposition: -0-
	(iv)	Shared power to dispose or direct the disposition: 54,106
C.	ProQuest Associates II LLC
(a)	Amount beneficially owned: 1,329,463
(b)	Percent of class: 6.3%
(c)	(i)	Sole power to vote or direct the vote: -0-
	(ii)	Shared power to vote or direct the vote: 1,329,463
	(iii)	Sole power to dispose or direct the disposition: -0-
	(iv)	Shared power to dispose or direct the disposition: 1,329,463
D.	ProQuest Management, LLC
(a)	Amount beneficially owned: 2,500
(b)	Percent of class: 0.1%
(c)	(i)	Sole power to vote or direct the vote: -0-
	(ii)	Shared power to vote or direct the vote: 2,500
	(iii)	Sole power to dispose or direct the disposition: -0-
	(iv)	Shared power to dispose or direct the disposition: 2,500
E.	Jay Moorin
(a)	Amount beneficially owned: 1,331,963
(b)	Percent of class: 6.3%
(c)	(i)	Sole power to vote or direct the vote: -0-

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	(ii)	Shared power to vote or direct the vote: 1,331,963
	(iii)	Sole power to dispose or direct the disposition: -0-
	(iv)	Shared power to dispose or direct the disposition: 1,331,963
F.	Alain Schreiber
(a)	Amount beneficially owned: 1,451,189
(b)	Percent of class: 6.8%
(c)	(i)	Sole power to vote or direct the vote: 119,226
	(ii)	Shared power to vote or direct the vote: 1,331,963
	(iii)	Sole power to dispose or direct the disposition: 119,226
	(iv)	Shared power to dispose or direct the disposition: 1,331,963

Item 5.

Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following. o

Item 6.

Ownership of More than Five Percent on Behalf of Another Person.

To the knowledge of the Reporting Persons, no other person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, a number of the Shares which represents more than five percent of the number of outstanding shares of the Shares.

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.

Certifications.

Each of the Reporting Persons hereby makes the following certification:

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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.

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SIGNATURE

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.

DATED: February 14, 2008
		/s/ Pasquale DeAngelis
		Pasquale DeAngelis, as a member of ProQuest Associates III LLC and on behalf of ProQuest Investments III, L.P.


		*
		Jay Moorin, individually


		*
		Alain Schreiber, individually

*By:	/s/ Pasquale DeAngelis
	Pasquale DeAngelis, Attorney-in-Fact

Index Exhibit

SCHEDULE 13G

Exhibit Number

Exhibit Description

24.1	Power of Attorney

99.2	Joint Filing Agreement

JOINT FILING AGREEMENT

In accordance with Rule 16a-3(j) and Rule 13d-1(k)(1) and under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of Forms 3, 4, 5 and Schedules 13D and 13G (including any and all amendments thereto) with respect to the Common Stock, par value $0.00l per share, of Optimer Pharmaceuticals, Inc., and further agree that this Joint Filing Agreement shall be included as an exhibit to such joint filings.

The undersigned further agree that each party hereto is responsible for the timely filing of such Forms 3, 4, 5 and Schedules 13D and l3G and any amendments thereto, and for the completeness and accuracy of the information concerning such party contained therein; provided that no party is responsible for the completeness or accuracy of the information concerning any other filing party, unless such party knows or has reason to believe that such information is inaccurate.

This Joint Filing Agreement may be executed in one or more counterparts, each of which shall be deemed to be an original instrument, but all of such counterparts together shall constitute one agreement.

In evidence thereof, the undersigned, being duly authorized, hereby execute this Joint Filing Agreement this 14th day of February, 2008.

PROQUEST ASSOCIATES II, LLC
/s/ Pasquale DeAngelis
Name:		Pasquale DeAngelis
Its:		Member



PROQUEST INVESTMENTS II, L.P.

By:	ProQuest Associates II LLC
Its:	General Partner


/s/ Pasquale DeAngelis
Name:		Pasquale DeAngelis
Its:		Member

PROQUEST INVESTMENTS II ADVISORS FUND, L.P.

By:	ProQuest Associates II LLC
Its:	General Partner

/s/ Pasquale DeAngelis
Name:			Pasquale DeAngelis
Its:			Member



PROQUEST MANAGEMENT, LLC

/s/ Pasquale DeAngelis
Name:		Pasquale DeAngelis
Its:		Member

*
Jay Moorin

*
Alain Schreiber

*By:	/s/ Pasquale DeAngelis
	Pasquale DeAngelis
	Attorney-in-Fact Power of Attorney filed with the Schedule 13G with which this Joint Filing Agreement is filed as an exhibit

Dated: February 14, 2008
			/s/ Jay Moorin
			Jay Moorin



			/s/ Alain Schreiber
			Alain Schreiber