Cytotoxic and Antibacterial Isomalabaricane Terpenoids from the Sponge Rhabdastrella globostellata

Nine new isomalabaricane terpenoids (1-9) were isolated from the sponge Rhabdastrella globostellata of Ximao Island, together with 13 known ones (10-22). The structures were established by spectroscopic data interpretation and chemical calculations, as well as by comparison with spectroscopic data of known compounds. Notably, of the new isolates, hainanstelletin A (5) is the first representative of a nitrogenous isomalabaricane. The isolated compounds were evaluated against several cancer cell lines and two bacterial pathogens. In addition, moderate to strong antibacterial activities against Streptococcus pyogenes were also detected among geometric isomers 1, 2, and 10-12, with minimum inhibitory concentrations of 0.1-1.8 μg/mL.