Iridoid Monoterpene Biosynthesis in Insects: Evidence for a De Novo Pathway Occurring in the Defensive Glands of Phaedon armoraciae (Chrysomelidae) Leaf Beetle Larvae

摘要

Iridoids (methylcyclopentanoid mono-terpenes) form a large group of secondary metabolites which is widespread in insects and plants. Commonly occurring iridoids of insect origin include chrysomelidial, plagiodial, anisomor-phal, iridodial, nepetalactone and ac-tinidine (Fig. 1). Most iridoid-contain-ing insects, such as leaf beetle larvae , ants, stick insects, and rove beetles , use these compounds as defensive allomones. However, in . aphids, nepetalactone (and lactol) functions as a sex pheromone. Recently we have examined the later stages of iridoid biosynthesis in chrysomelid leaf beetle larvae and have identified a sequence of transformations that closely resemble those found in plants , Essentially, 8-hydroxygeraniol (presumably produced by ω-hydroxylation of geraniol) is oxidised to 8-oxogeranial, which is subsequently cyclised to plagiodial and chrysomelidial by a Michael-type addition.