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

Four new polyhydroxylated sterols are isolated from Marine sponge Callyspongia fibrosa collected from the Gulf of Mannar, western Bay of Bengal (India). The structural assignment is based on 1H and 13C NMR spectra. All sterols are based on the known 24S-24-methyl cholesterol 1 which is also isolated, and contain 3β,6β-dihydroxy system and 25-O-acetate as common features (except in the case of sterol 6 that has a Δ25 in the place of 25-OAc). Additional OH substitution is also present at 5α in 4a and at 8β in 5. A further 12β-OH is present in 6 and 7. The hydroxylation pattern is so far known only in coral sterols but is without a precedent in sponge sterols. The major steroid 4a showed antimalarial activity against Plasmodium falciparum on the chloroquine-resistant stain better than on the chloroquine-sensitive strain.