(S)-12-hydroxygeranylgeraniol-derived diterpenes from the brown alga Bifurcaria bifurcata.

Four novel diterpenes were isolated from the brown alga Bifurcaria bifurcata collected off the Atlantic coast from Morocco, and their structures established by spectral and chemical methods. These compounds are acyclic diterpenes derived from (S)-12-hydroxygeranylgeraniol. One of them is its dehydration product at C-12, while the others are its oxidation derivatives: the methyl ester of the acid at C-1 and two stereoisomers (Z and E) of the aldehyde at C-1. These results are discussed from a chemotaxonomic point of view.

(S)-13-hydroxygeranylgeraniol-derived furanoditerpenes from Bifurcaria bifurcata.

Two new diterpenes were isolated from a sample of the brown alga Bifurcaria bifurcata collected from Brittany on the Atlantic coast and their structures established by spectroscopic methods. The new diterpenes are derived from (S)-13-hydroxygeranylgeraniol by terminal cyclization and oxidation leading to a furan-3-yl ring or a beta,gamma-epoxy-gamma-lactone. One of them showed a cytotoxic effect to fertilized sea urchin eggs. The chemical shifts of the methyl groups and quaternary carbons in (S)-13-hydroxygeranylgeraniol have been revised to take account of the results obtained in a 2D NMR long-range C-H correlation experiment and the absolute configuration at C-13 determined for the first time. The geographical variation in the diterpenoid composition of B. bifurcata was also studied.