Pyrrolidine-5,5-trans-lactams. 1. Synthesis and incorporation into inhibitors of hepatitis C virus NS3/4A protease

[reaction: see text] In this, the first of two letters, we outline the use of the pyrrolidine-5,5-trans-lactam template to design small, neutral, mechanism-based inhibitors of hepatitis C NS3/4A protease. The hitherto unreported reaction of the acyl iminium ion precursor 4 with dialkyl-substituted silyl ketene acetals (e.g., 8b) is described. Compound 12b, with a spirocyclobutyl P1 substituent and a cyclopropylacyl substituent on the lactam nitrogen, has a k(obs)/I of 400 M(-)(1) s(-)(1) and demonstrates activity in a replicon cell-based surrogate HCV assay.