New sesquiterpenes from the soft coral Litophyton arboreum

Two new sesquiterpenes; 8α,11-dihydroxy-β-cyperon (2), and 5-epi-7α-hydroxy-( +)-oplopanone (3), were isolated from the soft coral Litophyton arboreum, together with nine known ones, including five sesquiterpenes; 11-hydroxy-8-oxo-β-cyperon (1), alismoxide (4), 5β,8β-epidioxy-11-hydroxy-6-eudesmene (5), chabrolidione B (6), 7-oxo-tri-nor-eudesm-5-en-4β-ol (7), two sterols; 7β-acetoxy-24-methyl-cholesta-5,24(28)-diene-3β,19-diol (8), nebrosteroid M (9), and two glycerol derivatives; chimyl alcohol (10) and batyl alcohol (11). The structures of the isolated compounds were characterized using spectroscopic techniques, predominately HR-ESI-MS, 1D, 2D-NMR, and ECD analyses. Compounds 1-11 were evaluated for their cytotoxic activity against three human cancer-cell lines (A549, MCF-7 and HepG2), and anti-leishmanial potential against the causal parasite, Leishmania major. Compounds 4, 8, and 9 exhibited potent cytotoxic activity against the A549 cell line (IC₅₀ = 17.0 ± 2.5, 13.5 ± 2.1, and 16.5 ± 1.3 μg/ml, respectively) as compared with the standard antitumor agent etoposide (IC₅₀ 28.4 ± 4.5 μg/ml). In addition, compound 9 exhibited remarkable cytotoxic activity against MCF-7 cell line (IC₅₀ = 24.7 ± 2.1 μg/ml: 22.2 ± 4.2 μg/mL for etoposide).