Research and development of a second-generation process for oseltmivir phosphate, prodrug for a neuraminidase inhibitor

A second-generation manufacturing process from a shikimic acid-derived epoxide to oseltamivir phosphate features a magnesium chloride-amine complex-catalyzed ring opening of the epoxide by tert-butylamine, a selective O-sulfonylation of the resulting tert-butylamino alcohol, a surprisingly efficient cleavage of a tert-butyl group from an aliphatic tert-butylamide, and the isolation of oseltamivir phosphate from a palladium-catalyzed allyl transfer reaction mixture. The overall yield from the epoxide to oseltamivir phosphate has been increased from 27 to 29% or 35-38% for two previous processes, respectively, to 61%.