Synthetic Biologics Announces Closing of Recent Equity Offering and Exercise in Full of Underwriters' Over-Allotment Option

ROCKVILLE, Md., July 21, 2015 /PRNewswire/ -- Synthetic Biologics, Inc. (NYSE MKT: SYN), a clinical-stage company focused on developing therapeutics to protect the microbiome while targeting pathogen-specific diseases, today announced that it has closed the public offering of 15.3 million shares of common stock, including the fully exercised over-allotment option by the underwriters covering 2.0 million shares, at an offering price of $3.00 per share. The total gross proceeds of the offering, including the exercise in full of the over-allotment option, were approximately $46.0 million. Net proceeds to the Company, after deducting the underwriters' discount and other estimated expenses, are expected to be approximately $42.6 million.

The Company anticipates using the net proceeds from the offering to fund its clinical programs including Phase 2 clinical candidates, SYN-004 for the prevention of C. difficile and SYN-010 for the treatment of irritable bowel syndrome with constipation (IBS-C), research & development, potential licensing and acquisition of intellectual property, investments in and acquisition of complementary businesses or partnerships, and for general corporate purposes.

William Blair & Company, L.L.C. and RBC Capital Markets, L.L.C. are the joint book-running managers for the offering. BTIG, LLC is serving as co-manager for the offering.

A preliminary prospectus supplement and a final prospectus supplement relating to these securities have been filed with the SEC and are available at the SEC's website at www.sec.gov. Copies of the preliminary prospectus supplement and the final prospectus supplement may also be obtained from William Blair & Company, L.L.C., Attention: Prospectus Department, 222 West Adams Street, Chicago, Illinois 60606, by telephone at (800) 621-0687, or by email at [email protected]. RBC Capital Markets, L.L.C., Attention: Equity Syndicate, 200 Vesey Street, 8th Floor, New York, NY 10281-8098, or by telephone at (877) 822-4098.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of such jurisdiction.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE MKT: SYN) is a microbiome-focused, clinical-stage company developing therapeutics to protect the microbiome while targeting pathogen-specific diseases. The Company's lead candidates in Phase 2 development include SYN-004 which is designed to protect the gut microbiome from the effects of certain commonly used intravenous (IV) antibiotics for the prevention of C. difficile infection and antibiotic-associated diarrhea (AAD), and SYN-010 which is intended to reduce the impact of methane producing organisms in the gut microbiome to treat the underlying cause of irritable bowel syndrome with constipation (IBS-C). In addition, the Company is developing a Phase 2 oral estriol drug for the treatment of relapsing-remitting multiple sclerosis (MS) and cognitive dysfunction in MS, and a monoclonal antibody combination for the treatment of Pertussis. For more information, please visit Synthetic Biologics' website at www.syntheticbiologics.com.

This release includes forward-looking statements on Synthetic Biologics' current expectations and projections about future events. In some cases forward-looking statements can be identified by terminology such as "may," "should," "potential," "continue," "expects," "anticipates," "intends," "plans," "believes," "estimates," and similar expressions. These statements are based upon current beliefs, expectations and assumptions and are subject to a number of risks and uncertainties, many of which are difficult to predict and include statements with respect to this offering and the successful execution of the Company's business strategy, including its intended use of proceeds. The forward-looking statements are subject to risks and uncertainties that could cause actual results to differ materially from those set forth or implied by any forward-looking statements. Important factors that could cause actual results to differ materially from those reflected in Synthetic Biologics' forward-looking statements include, among others, the additional clinical studies and results not meeting expectations, the inability to commence and complete clinical trials when anticipated and other factors described in Synthetic Biologics' report on Form 10-K for the year ended December 31, 2014 and any other filings with the SEC. The information in this release is provided only as of the date of this release, and Synthetic Biologics undertakes no obligation to update any forward-looking statements contained in this release on account of new information, future events, or otherwise, except as required by law.

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SOURCE Synthetic Biologics, Inc.