摘要：Positional isomers of naturally occurring peptide subunits were synthesized via highly diastereoselective reduction of tert -butylsulfinyl ketimines as a key reaction. While NaBH4 reduction of ketimines derived from 2-thiazolyl ketones afforded the ( R S, R )-isomer with moderate diastereoselectivity, L-Selectride® reduction afforded the ( R S, S )-isomer as the sole product. In contrast, ketimines derived from tert -butyl 2-thiazolyl ketone afforded the ( R S, R )-isomer with low diastereoselectivity by both NaBH4 and L-Selectride® reduction. Stereochemistry of the reaction was discussed based on calculation of the conformational energies for ketimines.
