S-1MEF

As filed with the Securities and Exchange Commission on April 25, 2007

Registration No. 333-            

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Oscient Pharmaceuticals Corporation

(Exact name of registrant as specified in its charter)

Massachusetts	04-2297484
(State or other jurisdiction of incorporation or organization)	(I.R.S. Employer Identification No.)

1000 Winter Street, Suite 2200

Waltham, Massachusetts 02451

(781) 398-2300

(Address, including ZIP code, and telephone number, including area code, of registrant’s principal executive offices)

Philippe M. Maitre

Oscient Pharmaceuticals Corporation

1000 Winter Street, Suite 2200

Waltham, Massachusetts 02451

(781) 398-2300

(Name, address, including ZIP code, and telephone number, including area code, of agent for service)

Copies to:

Joseph D. Vittiglio, Esq. Oscient Pharmaceuticals Corporation 100 Winter Street, Suite 2200 Waltham, MA 02451 (781) 398-2300 Patrick O’Brien, Esq. Ropes & Gray LLP One International Place Boston, MA 02110 (617) 951-7000 Danielle Carbone, Esq. Shearman & Sterling LLP 599 Lexington Avenue New York, NY 10022 (212) 848-4000 Abigail Arms, Esq. Shearman & Sterling LLP 801 Pennsylvania Avenue, N.W. Washington, D.C. 20004 (202) 508-8000

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this Registration Statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended (Securities Act), check the following box.  ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  x    333-141309

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

Calculation of Registration Fee

Title of Each Class of Securities to be Registered	Amount to be Registered	Proposed Maximum Aggregate Offering Price	Amount of Registration Fee
3.50% Convertible Senior Notes due 2011	$10,000,000	$10,000,000	$307.00
Common Stock, $0.10 par value per share(1)	80,000	$1,080,000	$33.16
Total Registration Fee			$340.16

⁽¹⁾ The shares of common stock that are being registered include 80,000 shares that could be issued if the Registrant elects under the terms of the new notes to make payments of additional interest in common shares instead of cash. Also includes an indeterminate number of shares of common stock issuable upon conversion of the new notes registered hereby, which shares are not subject to an additional fee pursuant to Rule 457(i) of the Securities Act. Pursuant to Rule 416 under the Securities Act, such number of shares of common stock registered hereby shall include an indeterminate number of shares of common stock that may be issued in connection with stock splits, stock dividends, recapitalizations or similar events.

This Registration Statement shall become effective upon filing with the Commission in accordance with Rule 462(b) under the Securities Act of 1933.

Incorporation of Certain Information By Reference

This Registration Statement is being filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended, solely to register an additional $10,000,000 aggregate principal amount of 3.50% Convertible Senior Notes due 2011 (the “New Notes”) of Oscient Pharmaceuticals Corporation, a Massachusetts corporation (the “Company”) and the shares of the Company’s Common Stock, par value $.10 per share, issuable upon conversion of or in connection with such New Notes. The contents of the Registration Statement on Form S-1 (No. 333-141309), filed by the Company with the Securities and Exchange Commission (the “Commission”) on March 15, 2007, as amended by Amendment No. 1 to Registration Statement on Form S-1 filed with the Commission on March 29, 2007, and Amendment No. 2 to Registration Statement on Form S-1 filed with the Commission on April 18, 2007, including the exhibits thereto, are incorporated by reference into this Registration Statement.

The required opinions and consents are listed on an Exhibit Index attached hereto and filed herewith.

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

All exhibits filed with or incorporated by reference in Registration Statement No. 333-141309 are incorporated by reference into, and shall be deemed to be a part of, this registration statement, except for the following, which are filed herewith.

Exhibit No.	Description
5.1	Opinion of Ropes & Gray LLP
23.1	Consent of Ernst & Young LLP, Independent Registered Public Accounting Firm
23.2	Consent of Ropes & Gray LLP (included in Exhibit 5.1)

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Waltham, The Commonwealth of Massachusetts, on April 25, 2007.

OSCIENT PHARMACEUTICALS CORPORATION
	/S/    STEVEN M. RAUSCHER
Name:	Steven M. Rauscher
Title:	Director, President and Chief Executive Officer

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/s/    STEVEN M. RAUSCHER         Steven M. Rauscher	Director, President and Chief Executive Officer (Principal Executive Officer)	April 25, 2007
/s/    PHILIPPE M. MAITRE         Philippe M. Maitre	Senior Vice President and Chief Financial Officer (Principal Financial and Accounting Officer)	April 25, 2007
* David K. Stone	Director and Chairman of the Board	April 25, 2007
* Gregory B. Brown	Director	April 25, 2007
* Walter Flamenbaum	Director	April 25, 2007
* Robert J. Hennessey	Director	April 25, 2007
* William R. Mattson	Director	April 25, 2007
* Gary Patou	Director	April 25, 2007
* William S. Reardon	Director	April 25, 2007
* Norbert G. Riedel	Director	April 25, 2007
* John E. Voris	Director	April 25, 2007

*By:	/s/    PHILIPPE M. MAITRE
	Philippe M. Maitre
	Attorney-In-Fact

EXHIBIT INDEX

Exhibit No.	Description
5.1	Opinion of Ropes & Gray LLP
23.1	Consent of Ernst & Young LLP, Independent Registered Public Accounting Firm
23.2	Consent of Ropes & Gray LLP (included in Exhibit 5.1)

EX-5.1

Exhibit 5.1

April 25, 2007

Oscient Pharmaceuticals Corporation

1000 Winter Street, Suite 2200

Waltham, Massachusetts 02451

Re: Registration Statement on Form S-1

Ladies and Gentlemen:

We have acted as counsel to Oscient Pharmaceuticals Corporation (“Oscient” or the “Company”), a Massachusetts corporation, in connection with the registration statement on Form S-1 (the “Registration Statement”), filed with the Securities and Exchange Commission pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the “Securities Act”). The Registration Statement relates to the registration by the Company of up to $10,000,000 aggregate principal amount of its 3.50% Senior Convertible Notes due 2011 (the “New Notes”) that the Company will offer for cash. The New Notes will be issued pursuant to an Indenture (the “Indenture”) by and between the Company and US Bank National Association, as Trustee (the “Trustee”). The Registration Statement also registers an indeterminate number of shares of the Company’s common stock, $0.10 par value per share (the “Common Stock”), into which the New Notes are convertible (the “Conversion Shares”), as well as the estimated number of shares of Common Stock that may be issued by the Company in the event the Company elects to pay additional interest on the New Notes in Common Stock instead of cash (“Interest Shares”).

In connection with this opinion, we have examined the Registration Statement and Indenture, which has been filed with the Commission as an exhibit to the Company’s Registration Statement of Form S-1, as amended (File No. 333-141309) (the “Original Registration Statement”). We have also examined originals or copies, certified or otherwise, identified to our satisfaction, of documents and records and have made investigation of fact and examination of law as we have deemed appropriate in order to enable us to render the opinions set forth herein. In conducting our investigation, we have relied, without independent verification, on the accuracy of certificates of public officials, offers and representatives of the Company and other appropriate persons.

In rendering the opinions set forth below, we have assumed that the Indenture is the valid and binding obligation of the Trustee.

The opinions expressed herein are limited to matters governed by The Commonwealth of Massachusetts, the State of New York and the federal laws of the United States of America.

Based upon and subject to the foregoing, we are of the opinion that:

1. When (a) the Registration Statement shall be effective in accordance with Rule 462(b) under the Securities Act, and (b) the New Notes shall have been issued, executed, authenticated and delivered in accordance with the Indenture and delivered as described in the Original Registration Statement and the Prospectus contained in the Original Registration Statement (the “Prospectus”) in exchange for cash, then the New Notes thus issued will constitute valid and binding obligations of the Company, enforceable against the Company in accordance with their terms.

2. When (a) the Registration Statement shall be effective in accordance with Rule 462(b) under the Securities Act, (b) the New Notes shall have been issued, executed, authenticated and delivered in accordance with the Indenture and delivered as described in the Original Registration Statement and Prospectus in exchange for cash, and (c) the Conversion Shares shall have been issued upon the conversion of the New Notes in accordance with the Indenture, then the Conversion Shares thus issued will have been duly authorized, validly issued, fully paid and non-assessable. Furthermore, in the event the Company elects to make additional interest payments to holders of New Notes in Interest Shares in accordance with the Indenture, the Interest Shares thus issued will have been duly authorized, validly issued, fully paid and non-assessable.

Our opinions set forth above are subject of (a) bankruptcy, insolvency, reorganization, moratorium and other similar laws of general application affecting the rights and remedies of creditors and secured parties, (b) general principles of equity and (c) the effects of the possible judicial application of foreign laws or foreign governmental or judicial action affecting creditors’ rights.

We hereby consent to your filing this opinion as an exhibit to the Registration Statement and to the use of our name therein and in the Prospectus under the caption “Legal Matters.” By giving the foregoing consent, we do not admit that we come within the category of persons whose consent is required under Section 7 of the Securities Act.

Very truly yours,

/s/ ROPES & GRAY LLP

Ropes & Gray LLP

EX-23.1

Exhibit 23.1

Consent of Ernst & Young LLP, Independent Registered Public Accounting Firm

We consent to incorporation by reference of our report dated March 12, 2007, with respect to the consolidated financial statements and schedule of Oscient Pharmaceuticals Corporation in this Registration Statement on Form S-1 filed pursuant to Rule 462(b), and included in the Registration Statements (Form S-1 No. 333-141309 and Form S-4 No. 333-141308) and related Prospectus of Oscient Pharmaceuticals Corporation for the exchange of the 3.5% Convertible Senior Notes due 2011 and the 5.0% Convertible Promissory Notes due 2009 and the sale of up to $60,000,000 3.50% Convertible Senior Notes due 2011.

/s/ ERNST & YOUNG LLP

Boston, Massachusetts

April 23, 2007