Diastereo- and enantioselective synthesis of a conagenin skeletal amide moiety

A synthetic study was carried out to obtain epimers of a protected 2,4-dihydroxy-3-methylpentanoic ester 9, which is a central building block of the immunomodulator (+)-conagenin 1. The configuration of the three contiguous stereogenic centers was determined by NMR measurements and comparison with the stereogenic centers of lactone 10.