Total syntheses and absolute stereochemistry of decarestrictines C1 and C2

The total syntheses of decarestrictines C1 and C2 have been described. The synthetic strategy involves a practical and flexible approach using esterification and ring-closing metathesis to unite the acid and alcohol fragments. The acid fragments are enantiomers of each other and have been prepared from l-(−)-malic acid via similar transformations; in Sharpless asymmetric epoxidation, (+)-DET has been used for decarestrictine C1 and (−)-DET for decarestrictine C2. The alcohol fragment is identical for both decarestrictines C1 and C2 and has been accessed from d-(+)-mannitol. Comparison of the 1H and 13C NMR data combined with the computational studies predicts the presence of two conformations without and with hydrogen bonding (conformational isomers I and II for decarestrictine C1), respectively. The 1H and 13C NMR data for decarestrictine C2 completely agreed with the analytical data reported by Kibayashi et al.