New polyhydroxy sterols from the marine sponge Callyspongia fibrosa (Ridley & Dendly)

Four new polyhydroxylated sterols and two known sterols are isolated from marine sponge Callyspongia fibrosa collected from the Gulf of Mannar, western Bay of Bengal (India). The sterols contain 3β,6β-dihydroxy system and 25-O-acetate as common features. The hydroxylation pattern is without a precedent in sponge sterols although known in coral sterols. The major steroid 4a showed antimalarial activity against Plasmodium falciparum on the chloroquine-resistant stain better than on the chloroquine-sensitive strain.