Geranium defensive agents. III. Structural determination and biosynthetic considerations of anacardic acids of geranium

Ozonolysis, dithioether derivatization, and EI and CI mass spectrometry were used to establish the location of the double bond in the side chain of the two major anacardic acids in geranium (Pelargonium hortorum) trichome exudate. The point of unsaturation was shown to be between C-5 and C-6 counting from the methyl end of the side chain, contradicting the earlier hypothesis that the olefmic bond was probably at the 9–10 position based upon expected biosynthetic considerations. The two major components are thus 6-(Z)-10-pentadecenyl]salicylic acid (C₂₂H₃₄O₃) and 6-(Z)-12-heptadecenyl] salicylic acid (C₂₄H₃₈O₃). This may indicate that the precursor of these anacardic acids is a saturated fatty acid since the location of a double bond at the 5–6 position is unusual among the unsaturated fatty acids. Capillary GLC and HPLC of the trichome exudate indicated the presence of small amounts of other anacardic acid analogs possessing such features as odd numbers of carbon atoms and saturated side chains.