Caffeoyltartronic acid from catnip (Nepeta cataria): A precursor for catechol in lubber grasshopper (Romalea guttata) defensive secretions.

Adults of the lubber grasshopper (Romalea guttata) secrete increased amounts of catechol from their defensive glands when fed diets containing only catnip leaves (Nepeta cataria). Model compound bioassays showed that these insects were able to sequester and biomagnify simple phenols, such as catechol and hydroquinone, in their defense gland secretions. Excessive catechol secretions from caffeic acid-fortified diets indicated metabolic pathways exist to perform efficiently more complex biochemical conversions. Reverse-phase HPLC of methanol extracts of catnip revealed only one major caffeoyl-polyphenol as a possible precursor for the observed elevated catechol secretions, when this plant is fed to lubbers. The compound was shown to be caffeoyltartronic acid (CTA). During analysis of CTA by probe-MS or gas chromatography (of its silylated derivative), CTA decomposed by loss of carbon dioxide to form caffeoylglycolic acid (CGA), making identification by these methods ambiguous. Only fast atom bombardment mass spectrometry (FAB-MS, negative mode) gave a true molecular weight. Groundivy (Glecoma hederacea), a relative of catnip, was also shown to contain CTA. The mung bean (Phaseolus radiatus=Vigna radiata), a species totally unrelated to catnip, is the only other reported plant source of CTA. Catnip leaves were found to contain about twice as much CTA as mung bean leaves.