Brominated sesquiterpenes from the red alga Laurencia obtusa

Four new sesquiterpenes, (8R*)-8-bromo-10-epi-beta-snyderol (1), (8S*)-8-bromo-beta-snyderol (2), 5-bromo-3-(3'-hydroxy-3'-methylpent-4'-enylidene)-2,4,4-trimethylcyclohexanone (3), and the epoxide 4, have been isolated from the chloroform-methanol extract of Laurencia obtusa, together with the three known compounds alpha-snyderol (5), alpha-snyderol acetate (6), and stigmasterol. The structures of the isolated compounds were elucidated through spectroscopic analyses. Compound 1 showed antimalarial activity, with IC50 values of 2700 and 4000 ng/mL against the D6 and W2 clones of Plasmodium falciparum, respectively.