Development of a Scaleable Synthesis of a 3-Aminopyrazinone Acetamide Thrombin Inhibitor

A scaleable route to 2-{3-[(2,2-difluoro-2-(2-pyridyl)ethyl)amino]-6-chloro-2-oxohydropyrazinyl}-N-[(3-fluoro(2-pyridyl))- methyl]acetamide 1 is described in which various scaleup issues were addressed to provide a safe, efficient, and robust route for the preparation of multi-kilo amounts of the compound. The use of expensive and toxic reagents, notably sodium azide, TMS-cyanide, and Deoxo-Fluor, and the need for specialist equipment were overcome in the preparation of the key fluorinated intermediates 2,2-difluoro-2-(2-pyridyl)ethylamine 3 and 2-aminomethyl-3-fluoropyridine 2. With minimal isolations and through processing of intermediates, the thrombin inhibitor 1 was isolated in 36% overall yield.