Abstract

In this communication we describe a much improved methodology for the synthesis of the selective β₂-adrenoceptor antagonist ICI 118551 (1), a procedure which overcomes capricious fractional crystallization and epoxidation methodologies described for its original preparation. Our approach involving a bromohydrin precursor to the key epoxide intermediate (7) yielded an 85 : 15 mixture of the in threo/erythro isomers of (7) which could be conveniently separated by flash chromatography on amine-pretreated silica. This new approach proved much more successful than attempts to separate the precursor alkene isomers (6) by fractional crystallization as described in the original patent literature. The product (1) obtained by using our methodology was found to have identical pharmacological properties to authentic ICI 118551 when tested both in vitro and in vivo.