Tetraprenyltoluquinols from the brown alga Cystophora fibrosa.

Six cyclised tetraprenyltoluquinols and five stereoisomers with the previously reported amentol skeleton have been isolated from the lipophilic extract of the South African brown alga Cystophora fibrosa. Structures and relative stereochemistry were determined using spectrometric techniques, particularly 1D and 2D NMR, and molecular modelling experiments. The compounds isolated appear to be enantiomeric to compounds with the same skeleton isolated from brown algae of the genus Cystoseira collected in northern Africa and the Mediterranean Sea. The isolation of tetraprenyltoluquinols with the amentol skeleton from this alga suggests that C. fibrosa should be moved from the genus Cystophora into the Cystoseira.