Tubercidin, a cytotoxic agent from the marine sponge Caulospongia biflabellata

Tubercidin (1), a known nucleoside antibiotic, was isolated as the major metabolite from a marine sponge Caulospongia biflabellata. Compound 1 exhibited potent cytotoxic activity against P388 and A549 tumor cells. The isolation, structure elucidation and biological activities of tubercidin (1) are described. This is the first report of the isolation of tubercidin from a marine organism.