Synthetic Biologics, Inc. (NYSE MKT: SYN), a late-stage clinical company developing therapeutics focused on the gut microbiome, today announced the closing of its previously announced underwritten public offering of 25,000,000 shares of its common stock and accompanying warrants to purchase 50,000,000 shares of its common stock at a price to the public of $1.00per share and accompanying warrants. The total gross proceeds of the offering were $25.0 million. Net proceeds to Synthetic Biologics, excluding the proceeds, if any from the exercise of the warrants, after deducting the underwriter's discount and other estimated expenses, are expected to be approximately $23.3 million. If exercised in full, the warrants could result in additional net financing proceeds to the Company of $78.8 million. The underwriter has a 30-day option from the day of pricing to purchase up to 3,750,000 additional shares of common stock and warrants to purchase up to 7,500,000 additional shares of common stock.

Cantor Fitzgerald & Co. acted as the sole book-running manager for the offering.

About Synthetic Biologics, Inc.

Synthetic Biologics, Inc. (NYSE MKT: SYN) is a late-stage clinical company developing therapeutics focused on the gut microbiome. The Company's lead candidates poised for Phase 3 development are: (1) SYN-010 which is intended to reduce the impact of methane producing organisms in the gut microbiome to treat an underlying cause of irritable bowel syndrome with constipation (IBS-C), and (2) SYN-004 (ribaxamase) which is designed to protect the gut microbiome from the effects of certain commonly used intravenous (IV) beta-lactam antibiotics for the prevention of C. difficile infection, antibiotic-associated diarrhea (AAD) and the emergence of antibiotic-resistant organisms. The Company is also developing preclinical stage monoclonal antibody therapies for the prevention and treatment of pertussis and novel discovery stage biotherapeutics for the treatment of phenylketonuria (PKU).