7-Epizingiberene, A novel bisabolane sesquiterpene from wild tomato leaves

Abstract

A C 15 hydrocarbon isolated from the leaves of 2 wild tomato species, Lycopersicon hirsutum f glabratum PI 199381 and Lycopersicon hirsutum PI 365906, has been identified as 7 - epizingiberene ( 2), a diastereomer of zingiberene ( 1) that occurs in essential oil of ginger. The structure assignment for 2 is based upon its 1H NMR, 13C NMR, IR, UV, and mass spectral characteristics. All spectral data for zingiberene and epizingiberene are identical except for 9 of 15 13C NMR resonances, which establish the diastereomeric relationship of these sesquiterpenes. The 4 S, 7 R stereochemistry of epizingiberene was proven by dehydrogenation to (7 R)- ar - curcumene ( 4). The opposite 7 R and 7 S stereochemistry of the zingiberenes implicates the probable occurrence of opposite sidechain rotations of a common ( S)-bisabolyl carbocation intermediate ( 1OA) to allow stereoelectronically favorable hydride shifts in their respective biosyntheses from ( E, E)-farnesyl diphosphate.