Stereoselective total synthesis of both (6R,9R,10S,7E)- and (6S,9R,10S,7E)-epimers of oxylipin (9R,10S,7E)-6,9,10-trihydroxyoctadec-7-enoic acid

An asymmetric synthesis of both the stereoisomers (2a & 2b) of the structure 2 proposed for (9R,10S,7E)-6,9,10-trihydroxyoctadec-7-enoic acid, an immunostimulant oxylipin from the n-butanol extract of the corms of Dracontium loretense, has been accomplished. The key steps involved are using Jacobsenʹs hydrolytic kinetic resolution (HKR), Julia–Kocienski olefination, regioselective epoxide ring opening and Wittig olefination. The configuration (9R,10S,7E)-6,9,10-trihydroxyoctadec-7-enoic acid was established as 2a from comparison of NMR data, HPLC analysis and [α]D values of naturally derived (9R,10S,7E)-6,9,10-trihydroxyoctadec-7-enoic acid, and comparison with the synthetic diastereomers 2a and 2b.