Two new terpenoidal derivatives: a himachalene-type sesquiterpene and 13,14-secosteroid from the soft coral Litophyton arboreum

From diethyl ether fraction of the Red Sea soft coral, Litophyton arboreum, two new terpenoidal derivatives, himachalene-type sesquiterpene (3α,6α-epidioxyhimachal-1-ene, 1) and secosteroidal derivative (22-norerogostane derivative, 13,14-seco-22-norergosta-4,24(28)-dien-19-hydroperoxide-3-one, 2), were identified. In addition to di-acetyl cembranoid derivative, (3) was isolated for the first time from the nature. Along with three known metabolites, sarcophytol M (4), 7β-acetoxy-24-methylcholesta-5-24(28)-diene-3,19-diol (5) and erythro-N-dodecanoyl-docosasphinga-(4E,8E)-dienine (6) were obtained. Spectroscopic measurements including 1D and 2D NMR were used for identification of chemical structures. All compounds were evaluated to assess their antiproliferative effect toward three different cancer cell lines MCF-7 (human breast carcinoma), HCT116 (human colon cancer) and HepG-2 (human hepatic carcinoma) in comparison with standard anticancer drug (Doxorubicin) by employing SRD assay. Compound 3 showed significant antiproliferative activities to MCF-7 (IC50 19.1 ± 0.032 µM), to HepG2 (IC50 24.0 ± 0.032 µM) and to HCT116 (IC50 22.0 ± 0.092 µM). The antiproliferative activities of 3 can be attributed, at least partly, to their ability to do cell cycle arrest, particularly, in G0/G1 and S phases.