CLAVOSINES A-C FROM THE MARINE SPONGE MYRIASTRA-CLAVOSA - POTENT CYTOTOXINS AND INHIBITORS OF PROTEIN PHOSPHATASE-1 AND PROTEIN PHOSPHATASE-2A

Clavosines A (1) and B (2), novel metabolites closely related to calyc ulins and calyculinamides, have been isolated from the marine sponge M yriastra clavosa. Clavosine C (3) was also isolated and is assumed to be an artifact from clavosine B (2). Structures of these compounds wer e determined by spectroscopic analysis and by comparison of their NMR data with those of the calyculins and calyculinamides. Clavosines A an d B were found to be very potent cytotoxins in the National Cancer Ins titute's screening panel of 60 tumor cell lines and were potent inhibi tors of the type 1 and 2A serine/threonine protein phosphatases.