Marine dinoflagellates of the genus Amphidinium have been recognized as a rich source of novel bioactive substances with unique structures. We previously isolated a series of cytotoxic macrolides, designated amphidinolides, possessing unique structural features from several strains of the dinoflagellates Amphidinium sp., among which the strain Y-5 was the richest source of the amphidinolides. Further search for metabolites from the strain Y-5, which was a symbiont of Okinawan marine acoel flatworm Amphiscolops sp., resulted in the isolation of two novel polyhydoroxyl compounds, colopsinols A (1) and B (2), belonging to a new class of polyketide metabolites. The structures of 1 and 2 were elucidated on the basis of extensive NMR techniques including a newly developed 2D NMR experiments such as CH_2-selected editing HSQC (E-HSQC) as well as FABMS/MS data. Colopsinols A (1) and B (2) are new class of polyketide natural products consisting of C_<56> and C_<53>-liner carbon chains, respectively, possessing a gentiobioside (β-D-glucopyranosyl-(1-6)-β-D-glucopyranoside) moiety and a sulfate ester. From this strain (Y-5), 13 cytotoxic macrolides, amphidinolides A-D, J, K, and M-S, have been isolated so far. Biosynthetically it is interesting that quite different type of polyketides such as colopsinols and amphidinolides are produced from the same dinoflagellate. Colopsinol A (1) showed inhibitory activity against DNA polymerase α and β with IC_<50> values of 13 and 7μM, respectively.
