Cytotoxic polyacetylenes from the Red Sea sponge Siphonochalina siphonella.

Two new polyacetylenes, callyspongenol-D (1) and callyspongendiol (2), the known polyacetylene dehydrosiphonochalynol (3), and the known triterpenoid sipholenol-A (4) were isolated from the Red Sea sponge Siphonochalina siphonella. Their chemical structures were elucidated on the basis of spectroscopic analyses. The cytotoxicity of the isolated compounds towards the human mammary carcinoma cell line MCF-7 was determined by the lactate dehydrogenase (LDH) assay, and compounds 4 and 1 were found to be the most toxic of the four, with IC50 values of 8.8 and 11.7 microM, respectively.