Absolute configuration of volicitin from the regurgitant of lepidopteran caterpillars and biological activity of volicitin-related compounds

Volicitin [N-(17-hydroxylinolenoyl)-L-glutamine] and N-linolenoyl-L-glutamine are known as insect-produced plant volatile elicitors. The absolute configuration of the hydroxylinolenoyl moiety of volicitin from three noctuid species, Helicoverpa armigera, Mythimna separata and Spodoptera litura, was determined to be all 17S in high enantiomeric excess. When treated with 30 pmol of (17S)- and (17R)-volicitin, corn seedlings were induced, to release volatiles, there being no significant difference in the amount released between the two isomers. On the other hand, N-linolenoyl-L-glutamine was only about 30% as active as volicitin. Among several synthesized N-linolenoylamino acid conjugates, only the L-glutamine conjugate induced the emission of volatile organic compounds. These results show that the L-glutamine moiety of volicitin played a more critical role than the hydroxyl moiety, although both moieties affected the elicitor activity inducing the release of volatiles.