NEW HAVEN, Conn. (AP) — Achillion Pharmaceuticals said it will raise $50 million by selling stock to a group of four venture capital firms and company shares slid more than 5 percent in electronic trading early Thursday.

Domain Associates, Clarus Ventures, Quaker BioVentures, and Pappas Ventures will buy about 19.8 million shares at $2.49 per share, for gross proceeds of $50.1 million, the company said.

Achillion said Wednesday it will use the proceeds to test its hepatitis C drug candidate and other antiviral drugs.

The four investment firms will also receive warrants that could be converted into another 6.9 million Achillion shares. Each warrant costs 12.5 cents and will allow the investors to buy 0.35 shares of stock at any time over the next seven years. They will be exercisable at a price of $3.11 per share.

The offering is expected to close Friday.