Insect antifeedant sesquiterpene Acetals from the liverwort Lepidolaena clavigera.: 2.: Structures, artifacts, and activity

Clavigerin A (1) was isolated from the New Zealand liverwort Lepidolaena clavigera and shown to be a polyoxygenated bergamotane sesquiterpene with an unusual ring system. L clavigera shows infraspecific variation, since 1 was the only clavigerin detected in a North Island collection, whereas the previously reported clavigerins B (2) and C (3) were found in South Island collections with no sign of 1. Three new clavigerins, 4-6, were identified, but these are artifacts formed by alcoholysis of the acetoxy acetal group of the clavigerins 2 and 3, with either the extraction solvent ethanol or the RP column eluent methanol. The insect antifeedant and cytotoxic activities of these compounds are reported, and it is proposed that they act as hidden 1,4-dicarbonyl compounds.