Marine natural products. XXXI. Structure-activity correlation of a potent cytotoxic dimeric macrolide swinholide A, from the Okinawan marine sponge Theonella swinhoei, and its isomers.

Acidic treatment of swinholide A (1), which was characterized as the major cytotoxic macrolide from the Okinawan marine sponge Theonella swinhoei, provided several isomeric macrolides having different size of the dilactone ring structure. From the structure-activity correlation viewpoint, the in vitro cytotoxicities and in vivo antitumor activities of these dimeric macrolides, together with two monomeric macrolides which were synthesized from 1, have been examined.