BioCryst Pharmaceuticals Inc. signed a merger agreement with Exton, Pennsylvania-based Idera Pharmaceuticals, combining to biotechnology companies

Idera Pharmaceuticals is a biotechnology company with expertise in commercializing nucleic acid therapeutics to treat patients. It was founded in 1989.

Durham-based BioCryst Pharmaceuticals develops small molecule drugs that block key enzymes involved in uncommon diseases. The company was founded in 1986.

Once merged, the pharmaceutical companies will focus on the development and commercialization of medicines in order to serve more patients that suffer from rare diseases.

The combined company will be renamed once the deal is closed. The name has not yet been identified.

“Both of our companies have aspired to become successful providers for therapeutics for patients suffering from rare life-threatening diseases. Both share a culture that puts patients first and keeps their interests at the very core of what we do,” said Vincent Milano, Idera’s CEO, in a statement.

Milano will also be serving as a member of the board. Prior to Idera, Milano served as chief executive officer and president of ViroPharma Inc.

BioCryst chairman Robert Ingram will be the chairman of the combined company, and BioCryst CEO Jon P. Stonehouse will serve as a member of the board.

Each share of the BioCryst common stock will be exchanged for 0.50 shares of the new company stock and each share of Idera common stock will be exchanged for 0.20 shares of the new company stock.

BioCryst stockholders will own 51.6 percent of the combined company stock and Idera stockholders will own 48.4 percent. The stock exchange is expected to be tax free to stockholders.

BioCryst’s shares fell 27 cents, or 4.8 percent, to $5.32 in Monday trading. Idera’s shares fell 38 cents, or 14.9 percent, to $2.17.