Yardenone A and B: new cytotoxic triterpenes from the Indian Ocean sponge Axinella cf. bidderi.

Two new polyepoxysqualene-derived triterpenes, yardenone A (1) and B (2), together with the known yardenone (3) and sodwanone A (4), have been isolated from the marine sponge Axinella cf. bidderi from Yemen's Socotra Island in the Indian Ocean. The structures were elucidated using spectroscopic data. The relative stereochemistry was established by the analysis of ROESY spectra as well as coupling constants and molecular modeling. Furthermore, the absolute configuration of 1 was confirmed by the advanced Mosher's method. The cytotoxicity of these compounds was evaluated against a NSCLC cell line.