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 Jacobsen's 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.