New polyketides from dinoflagellate Amphidinium sp.

<p> Marine dinoflagellates have been recognized as a source of novel secondary metabolites with intriguing structures and interesting bioactivities. In our continuing search for bioactive metabolites from Okinawan marine dinoflagellates, we have isolated a series of macrolides, amphidinolides, and long chain polyketides such as colopsinols and luteophanols from cultured symbiotic marine dinoflagellates Amphidiniumspp. </p><p> Recently, we have investigated the culture medium of dinoflagellate Amphidiniumsp., which was a symbiont of a newly picked acoel flatworm Amphiscolops sp., and isolated five new liner polyketides, compounds 1~5, with known polyketides, amphidinin A (6) and amphidinolide Q (7). </p><p> The analysis of spectral data revealed that compounds 1~4were 4,5-seco-analogs of amphidinolide Q (7). The absolute configurations of 1~4 have been elucidated by the combination of J-based configuration analysis, modified Mosher’s method, and chemical derivatization. 1~4 corresponded to 4,5-secoamphidinolide Q, 4-O-β-D-ribofuranosyl-4,5-</p><p>secoamphidinolide Q, 6,O-6-dihydro-4,5-secoamphidinolide Q, and 4-O-β-D-ribo-</p><p>furanosyl-6,O-6-dihydro-4,5-secoamphidinolide Q, respectively. 2and 4 were the first glycoside related to amphidinolides. </p><p> The structure of compound 5 was elucidated to be a 9,12-O-seco-analog of amphidinin A (6) based on its spectral data. The absolute configuration of 5 has been elucidated to be 2R, 4R, 6S, 11R, and 12S by chemical shift comparison, J-based configuration analysis, and modified Mosher’s method.</p><p> The absolute configuration of amphidinin A (6), a known amphidinolide related liner polyketide, was also elucidated to be 2R, 4R, 6S, 9R, 11R, and 12S by the combination of J-based configuration analysis, modified Mosher’s method, and the density-functional theory calculations.</p><p> Compounds 1~7showed antimicrobial activities against some bacteria and/or fungi.</p>