TRANSFORMATION OF PLANT PYRROLIZIDINE ALKALOIDS INTO NOVEL INSECT ALKALOIDS BY ARCTIID MOTHS (LEPIDOPTERA)

Two new pyrrolizidine alkaloids (PAs) were isolated from adults of Creatonotos transiens, the larvae of which had ingested retronecine or ester alkaloids. The structure were elucidated by GC-MS and H-1 and C-13 NMR spectroscopy as O9-(2-hydroxy-3-methlpentanoyl)-retronecine (creatonotine) and its isomer O7-(2-hydroxy-3-methylpentanoyl)-retronecine (isocreatonotine). The 2-hydroxy-3-methylpentanoic acid obtained by hydrolysis of the creatonotines is the 2S,3S-stereoisomer. The creatonotines as well as accompanying trace amounts of callimorphine were shown to be synthesized by both sexes from dietary retronecine by esterification. If Creatonotos larvae had been fed with Gynura scandens as PA source, the insect PAs accounted for about 75% of total PAs isolated from adults, indicating that Creatonotos degraded plant PAs and subsequently re-esterified the resulting retronecine. This work provides definitive proof that an arctid moth is able to hydrolyse plant ester alkaloids and re-esterify the resulting necine base with acids which are intermediates of insect metabolism. PAs isolated from Creatonotos were exclusively present in the form of their N-oxides.