Athula B. ATTYGALLE
Baker Laboratory, Department of Chemistry, Cornell University,
Ithaca. N.Y. 14853, USA (Fax: 607 2553407)
Although a highly diverse set of secondary metabolites has been isolated from beetles, very little is known about the biosynthetic pathways by which these compounds are produced. Our biosynthetic investigations show that the major defensive alkaloid of the E. varivestis pupa, epilachnene (1)-1 is biosynthesized from oleic acid and L-serine-2. From GC/MS and GC/IR studies of alkaloid produced by Epilachna fed with deuteriated oleic acid, it is clear that oleic acid loses four carbon atoms from its carboxyl end during the biosynthesis. In addition, we have evidence to demonstrate that only the C- 15 methylene group of oleic acid is involved in the carbon-nitrogen bond formation between the fatty acid and amino acid moieties during the formation of the macrocyclic ring of epilachnene-3.
Unexpectedly, the oily droplets on the pupal integumental hairs of the squash beetle, E. borealis, does not appear to contain alkaloids at all, but consists of a mixture of a- ß- y- and d-tocopheryl acetates. In tact, this is the first report of the occurrence of acetate esters of any tocopherol in nature-4. By feeding a diet enriched with 5,7-bis(trideuteriomethyl)-a-tocopherol to squash beetle larvae, and subsequently analyzing the pupal secretion by GC-MS, we could establish that cu-tocopheryl acetate is biosynthesized from a-tocopherol present in the leaf diet of squash beetle larvae-5.
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