Processing of a sesquiterpene lactone by Papilio glaucus caterpillars

Papilio glaucus caterpillars encounter a diverse array of sesquiterpene lactones, including parthenolide, in the leaves of host plants Liriodendron tulipifera and Magnolia virginiana. These compounds are toxic to unadapted herbivores, and the development of P. glaucus caterpillars likely depends on their ability to excrete or detoxify them efficiently. A new metabolite of parthenolide, 2-alpha-hydroxydihydroparthenolide, identified by crystal structure determination and nuclear magnetic resonance, was present in the waste of the caterpillars. The parent compound was modified by the reduction of an alpha-methylene group, rendering the compound less reactive, and the addition of a hydroxyl group, which increases the polarity and prepares it for the conjugation reactions of phase II metabolism. Unmetabolized parthenolide was also present in large amounts in waste. P. glaucus larvae are apparently capable of excreting intact sesquiterpene lactones and sesquiterpene lactone metabolites during consumption of foliage rich in these compounds.