Synthetic Biologics Inc. closed its underwritten public offering for a combination of securities to raise $18.6 million in gross proceeds.

The Rockville, Md.-based company plans to use net proceeds from the offering to fund preclinical and clinical programs and for working capital and general corporate purposes.

Two kinds of units were offered: class A units consisting of 2,520,000 common shares and warrants to purchase 2,520,000 shares at a combined price of $1.15, and class B units consisting of 15,723 series B convertible preferred shares, which can be converted into an aggregate of 13,672,173 common shares, and warrants to purchase 13,672,173 common shares.

The warrants can be exercised upon issuance at a price of $1.38 and will expire five years after issuance.

Synthetic Biologics has given underwriters the option to purchase up to an additional 2,428,825 common shares and the same number of warrants to purchase common shares.

Alliance Global Partners acted as the sole book-running manager for the offering.

Synthetic Biologics is a late-stage clinical company that develops therapeutics designed to preserve the microbiome.