Two new 5,6-epoxysterols from calcareous marine sponge Leucetta chagosensis.

Chemical investigation on CH2Cl2 extract of the marine sponge Leucetta chagosensis, collected from the South China Sea, afforded two new 5,6-epoxysterols, 5α,6α-epoxycholesta-8(14),22(E)-diene-3ß,7α-diol (1) and (24R)-24-ethyl-5α,6α-epoxycholesta-8(14),22(E)-diene-3ß,7α-diol (2) along with ten known related steroid analogs (3-12). Their structures were elucidated on the basis of NMR spectroscopic analyses, and comparison with the literature. All isolates were tested for cytotoxicity against three tumor cell lines only known compounds 11 and 12 exhibited notable cytotoxic activity against A549 (IC50: 3.0 and 5.6 µM), PC9 (2.0 and 15.6 µM), and MCF-7 (9.4 and 11.8 µM) cell lines, respectively.