7-Epizingiberene, A Novel Bisabolane Sesquiterpene from Wild Tomato Leaves

Article abstract of DOI:10.1016/S0040-4020(01)89415-1

A C15 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 4S,7R stereochemistry of epizingiberene was proven by dehydrogenation to (7R)-ar-curcumene (4).The opposite 7R and 7S stereochemistry of the zingiberenes implicates the probable occurence of opposite sidechain rotations of a common (S)-bisabolyl carbocation intermediate (10A) to allow stereoelectronically favorable hydride shifts in their respective biosyntheses from (E,E)-farnesyl diphosphate.