Stereoselective synthesis of 4'-α-alkylcarbovir derivatives based on an asymmetric synthesis or chemoenzymatic procedure

Abstract

Stereoselective synthesis of 4'-α-alkylcarbovir derivatives 4 was described based on asymmetric synthesis or a chemoenzymatic procedure. The asymmetric alkylation of chiral acetal 7 gave the alkylated enol ethers 9a - c possessing a chiral quaternary carbon. The key carbocyclic intermediates 14a - c were synthesized from 9a - c via eleven-steps. Coupling of 14a - c with 2-amino-6-chloropurine followed by desilylation and subsequent hydrolysis afforded the target compounds 4a - c in moderate yield. The optically active cyclopentene intermediates 5a - c and 6a - c were also prepared by enzymatic resolution of (±)-5a - c and (±)-6a - c, respectively.