Cephalon has offered to buy the Australian company ChemGenex Pharmaceuticals for about $231 million, or 225 Australian dollars.

Cephalon's bid "has the unanimous support of the ChemGenex directors," who plan to recommend it to shareholders unless a better offer appears, the companies said in a statement on Monday.

The all-cash bid of 70 Australian cents per share represents a 59 percent premium to the last traded price of ChemGenex shares.

Cephalon also is offering 2 Australian cents for every Australian Securities Exchange-listed ChemGenex option.

The Australian company is seeking Food and Drug Administration approval to sell the injectable drug Omapro in the United States for chronic myeloid leukemia patients with a specific genetic mutation.

Cephalon in December signed a major partnership deal with Australia's Mesoblast Ltd for a variety of potential therapies in cardiovascular and neurological areas, and it also bought a 20 percent stake in the company.