Minor Metabolites from the Ascidian Stolonica socialis and Cytotoxicity of Stolonoxides

Bioassay guided isolation of the metabolites of the ascidian Stolonica socialis from Tarifa Island (Cádiz, Spain) led to a series of cyclic peroxides. A 9:1 mixture of stolonoxide A and the new stolonoxide B, a 6:4 mixture of their corresponding sodium salts, and a minor 6:4 mixture of the new stolonoxides C and D obtained as their sodium salts. Their structures were established by spectroscopic study of both the natural mixtures, whose constituents differ in the geometry of a double bond, and the corresponding methyl esters. The strong cytotoxicity exhibited by the stolonoxides against five tumor cell lines is presented and discussed.