The two new anti-dinoflagellates, clonostachysins A and B, were obtained from a marine sponge derived fungus Clonostachys rogersoniana strain HJK9. Their chemical structures were determined by spectroscopic studies as highly N-methylated cyclic peptides of the nine amino acids. The absolute stereochemistry was elucidated by the advanced Marfey's method. Both clonostachysins A and B exhibited a selectively inhibitory effect on a dinoflagellate Prorocentrum micans at 30 mM, but had no effect on other microalgae and bacteria even at 100 mM.Keywords clonostachysin, anti-dinoflagellate, cyclic peptides, marine, fungus Marine microorganisms are recognized as a promising source of novel natural products [1]. We have been screening marine-derived bacteria and fungi for antimicroalgal, antibacterial and anticancer activities to find novel bioactive substances. In the course of this screening, we found that an extract of the marine-derived fungus named HJK9, which had been isolated from a sponge, Halicondria japonica, collected in Numazu, Japan, had an inhibitory effect on the dinoflagellate, Prorocentrum micans. We have previously reported b -cyanoalanine as a specific inhibitor of cyanobacteria [2] and N-(3-hydroxy-1-oxotetradecyl)-leucine as an anti-dinoflagellate substance [3], but as far as we know, only a few substances have been reported outside our group as being antimicroalgal [4,5]. We describe in this note the isolation and structural determination of two new anti-dinoflagellates, clonostachysins A and B, from a marine-derived fungus.The clonostachysin-producing fungus (HJK9) was identified as Clonostachys rogersoniana from morphological studies and its 18S rDNA sequence. This fungus was cultured in potato dextrose broth, which had been prepared with artificial seawater (Tropic Marine ® ), for 7 days at 30°C under rotation at 100 rpm. The use of artificial seawater increased the productivity of the active substance by nearly a factor of two. The cultured broth was centrifuged, and the resulting supernatant was extracted with ethyl acetate. The ethyl acetate extract which exhibited anti-dinoflagellate activity was fractionated in a Sep Pak Florisil ® column with step-wise elution using chloroform/methanol mixtures (100% chloroform, 100 : 1, 10 : 1, and 100% methanol). The activity was detected in the first fraction (100% chloroform), and the active fraction was further purified by HPLC equipped with an ODS column (TSKgel ODS-80Ts, i.d. 4.6ϫ250 mm, Tosoh Corporation) with 50% aqueous methanol as the solvent. Clonostachysins A (4.0 mg) and B (2.5 mg) were obtained from 8 liter of the culture broth by purifying twice with HPLC. The physico-chemical properties of clonostachysins A and B are summarized in Table 1.The molecular formula of clonostachysin A was
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