Blurring the boundary between bio- and geohopanoids: Plakohopanoid, a C _(32) biohopanoid ester from Plakortis cf. lita

摘要

Plakohopanoid (3a), a new type of hopanoid derivative composed of a C _(32) hopanoid acid ester linked to a mannosyl-myo-inositol, was isolated from the sponge Plakortis cf. lita as its peracetyl derivative 3b. The structure of 3b was determined by a combination of spectroscopic analysis and micro-scale chemical degradation. Even though plakohopanoid was isolated from a sponge, its component parts are clearly of bacterial origin, and its bacterial biosynthesis is very likely. Until now, C _(32) hopanoic acids have been considered to be geohopanoids, i.e., diagenetic products that are formed through abiotic degradation of the biohopanoids present in bacteria. The presence of 3a in a marine living organism shows that there is a biosynthetic pathway to C _(32) hopanoic acids, and these substances should therefore no longer with certainty be considered to be geohopanoids.