7-EPIZINGIBERENE, A NOVEL BISABOLANE SESQUITERPENE FROM WILD TOMATO LEAVES

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 diastereome r of zingiberene (1) that occurs in essential oil of ginger. The struc ture assignment for 2 is based upon its H-1 NMR, C-13 NMR, IR, UV, and mass spectral characteristics. All spectral data for zingiberone and epizingiberene are identical except for 9 of 15 C-13 NMR resonances, w hich establish the diastereomeric relationship of these sesquiterpenes . The 4S, 7R stereochemistry of epizingiberene was proven by dehydroge nation to (7R)-ar-curcumene (4). The opposite 7R and 7S stereochemistr y of the zingiberenes implicates the probable occurrence of opposite s idechain rotations of a common (S)-bisabolyl carbocation intermediate (10A) to allow stereoelectronically favorable hydride shifts in their respective biosyntheses from (E, E)-farnesyl diphosphate.