New methylcyclopentanoid terpenes from the larval defensive secretion of a chrysomelid beetle (Plagiodera versicolora).

The defensive secretion of larvae of the chrysomelid beetle Plagiodera versicolora contains two unstable, volatile methylcyclopentanoid terpenes: a dialdehyde (chrysomelidial) isomeric with dolichodial and anisomorphal, and a closely related enol lactone (plagiolactone). Chrysomelidial and plagiolactone are shown to have structures III and IV on the basis of a detailed analysis of their spectra, coupled with chemical transformations to products of known structure.