Discovery of an orally active series of isoxazoline glycoprotein IIb/IIIa antagonists

Using isoxazoline XR299 (1a) as a starting point for the design of highly potent, long-duration GPIIb/IIIa antagonists, the effect of placing lipophilic substituents at positions α and β to the carboxylate moiety was evaluated. Of the compounds studied, it was found that the n-butyl carbamate 24u1,2 exhibited superior potency and duration of ex vivo antiplatelet effects in dogs. Replacement of the benzamidin-4-yl moiety with alternative basic groups, elimination of the isoxazoline stereocenter, and reversal of the orientation of the isoxazoline ring resulted in lowered potency and/or duration of action.