New Steroids and a New Alkaloid from the Gorgonian Isis minorbrachyblasta: Structures, Cytotoxicity, and Antilarval Activity

Two new polyoxygenated steroids, (1 alpha,3 beta,7 alpha,11 alpha,12 beta)-gorgost-5-ene-1,3,7,11,12-pentol 12-acetate (1) and 11-O-acetyl-22-epihippuristanol (2), and a new alkaloid. 2,3,5,6,11,11b-hexahydro-2-hydroxy-1H-indolizine[8,7-b]indole-2-carbox ylic acid (3), together with three known compounds. 22-epihippuristanol (4), hippuristanol (5), and tryptamine (6), were isolated from the EtOH/CH2Cl2 extracts of the South China Sea gorgonian Isis minorbruchyblasta. The structures of the new compounds were determined by spectroscopic methods. Compound 1 showed weak cytotoxicity against A549, HONE1. and He La cancer cell lines and strong anti larval activity towards Bugula neritina larvae with an EC50 value of 5.8 mu g/ml. Compound 5 showed moderate cytotoxicity against A549. HONE1, and He La cell lines, and the epimer mixture 4/5 (weight ratio 3 :2) exhibited potent cytotoxicity against A549 and HONE1 cell lines with IC50 values of 4.2 and 4.8 mu g/ml, which indicated that epimers 4 and 5 might have a synergistic effect on their cytotoxicity against A549 and HONE1 cell lines.