UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (date of earliest event reported): October 16, 2012

Synthetic Biologics, Inc.

(Exact name of registrant as specified in charter)

Nevada

(State or other jurisdiction of incorporation)

617 Detroit Street, Suite 100

Ann Arbor, MI 48104

(Address of principal executive offices and zip code)

(734) 332-7800

(Registrant’s telephone number including area code)

N/A

(Former Name and Former Address)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of registrant under any of the following provisions:

On October 16, 2012 a closing was held for the transaction previously announced on August 8, 2012 between Synthetic Biologics, Inc. (the “Company”) and Intrexon Corporation (“Intrexon”). The Company issued 3,552,210 shares of Company common stock (the “Shares”) at a purchase price equal to the $0.001 par value of such shares, which issuance is also deemed paid in partial consideration for the execution and delivery of the Exclusive Channel Collaboration Agreement, dated August 6, 2012, between the Company and Intrexon. The offer and issuance of the Shares have not been registered under the Securities Act of 1933, as amended (the “Securities Act”), and therefore may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements. For this issuance, the Company is relying on the exemption from federal registration under Section 4(2) of the Securities Act, based on the Company’s belief that the offer and sale of the Shares does not involve a public offering as Intrexon is an “accredited investor” as defined under Section 501 promulgated under the Securities Act and no general solicitation has been involved in the offering.

On October 16, 2012, the Company completed the closing of its Exclusive Channel Collaboration transaction with Intrexon, which was previously announced in the Company’s press release on August 8, 2012. The Company intends to use specified patents and other intellectual property of Intrexon in connection with the research, development, use, importing, manufacture, sale, and offer for sale of monoclonal antibody therapies for the treatment of eight specific target infectious disease indications (the “Field”). Initially, the Company’s development efforts will target three infectious diseases within the Field. Pursuant to the terms of the Stock Purchase Agreement between the Company and Intrexon dated August 6, 2012, the Company met all of the requisite closing conditions, including the receipt of NYSE MKT approval, and has issued the Shares to Intrexon, which issuance is deemed paid in partial consideration for the execution and delivery of the Exclusive Channel Collaboration Agreement, dated August 6, 2012, between the Company and Intrexon. Stockholder approval of such issuance was obtained at the Company’s Annual Meeting of Stockholders held on October 5, 2012.

In connection with the transactions contemplated by the Stock Issuance Agreement, and pursuant to the First Amendment to Registration Rights Agreement, the Company agreed to file a “resale” registration statement (the “Registration Statement”) registering the resale of the shares issued and to be issued under the Stock Issuance Agreement. None of the shares to be issued under the Stock Issuance Agreement need to be registered until April 30, 2013. Under that agreement, the Company will be obligated to use its reasonable best efforts to cause the “resale” registration statement to be declared effective as promptly as practicable after filing and to maintain the effectiveness of the registration statement until all securities therein are sold or are otherwise can be sold pursuant to Rule 144, without any restrictions.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.