Germacrene C → Cyclohexene, 4-ethenyl-4-methyl-3-(1-methylethenyl)-1-(1-methylethyl)-, (3R-trans)-

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Reaction Conditions

Reaction Steps

Preliminary studies, in which leaf extracts were compared to steam distillates by standard GC-MS methods (hot injector) and by cool on-column injection, revealed that the target metabolite, germacrene C (FIG. 1), was prone to thermal rearrangement to a compound with shorter GC retention time but nearly identical mass spectrum. This compound was absent in the pentane leaf extract when analyzed by cool (35° C.) on-column injection, but was present when the same pentane extract was injected onto a hot (230° C.) injector (FIG. 2). Comparison of this compound with authentic δ-elemene (FIG. 1) from black pepper oleoresin yielded an identical retention time and mass spectrum. Heating purified germacrene C in a sealed container to 130° C. for 1 h resulted in complete conversion to δ-elemene which was confirmed by GC-MS. Conversion of germacrene C to δ-elemene has been reported previously (Morikawa and Hirose, Tetrahedron Lett. 22:1799-1801, 1969). The sesquiterpene fraction of ‘VFNT Cherry’ leaves (3.2% of total volatile olefins) contained germacrene C (66%), germacrene A (7%), guaia-6,9-diene (7%), germacrene B (6%), β-caryophyllene (6%), germacrene D (4%), α-humulene (4%), and β-elemene (1%). This is the first report of azulane (guaia-6,9-diene) and germacrane skeletal types in tomatoes. By contrast, the sesquiterpene fraction of leaves from the commercial tomato variety ‘Better Boy’ (3.3% of total volatile olefins) contained mostly β-caryophyllene (71%), germacrene C (15%), and α-humulene (9%). The sesquiterpene composition of ‘Better Boy’ agrees with previous reports on the content of L. esculentum leaf oil (Buttery et al., J. Agric. Food Chem. 35:1039-1042, 1987; and Lundgren et al., Nord. J. Bot. 5:315-320, 1985), except that no δ-elemene was found by on-column injection; germacrene C has not been previously observed in Lycopersicon.

Provenance & Evidence