Two new cytotoxic polycyclic xanthones, actinoplanones A (1) and B (2) were isolated from the culture broth of Actinoplanes sp. R-304 by monitoring their bioactivity against HeLa cells. Compound 1 was extremely cytotoxic (IC50 0.00004^g/ml) against HeLa cells. The structures of 1 and 2 were established mainly by analyses of 2D heteronuclear correlation NMR experiments. The absolute configurations of the asymmetriccarbons of the compounds have been assigned to be 9R, 245, 25R and US by circular dichroism spectra and NMRanalysis using chiral derivatives (esters of a-methoxy-a-(trifluoromethyl)acetic acid).Our efforts to identify antitumor antibiotics from microorganisms^have resulted in the isolation of two potent cytotoxic compoundsagainst HeLa cells from the culture broth of Actinoplanes sp. R-304 (Actinoplanaceae). Since the structure determination study of the compoundsrevealed that they were new polycyclic xanthones, we named them actinoplanones A (1) and B (2). Actinoplanone A (1) was found to be a potent cytotoxin from in vitro assay with HeLacells. This paper deals with the fermentation, isolation and structure determination, including the absolute configurations, of 1 and2.Actinoplanones A (1) and B (2) were produced in the culture broth of Actinoplanes sp. R-304 which was isolated irom a iorest son sample collected in Okinawa Prefecture, Japan. The actinoplanones were isolated from the ethyl acetate extract of the broth through a combination of silica gel column chromatography and reversed-phase HPLC. Actinoplanone A (1), mp 276~278°C, [>]2D5-619.8°(CHCI3), showed a 3 : 1 chlorine-containing ion pair at mjz 584 and 586 in the electron impact mass spectrum (EI-MS). A molecular formula of C2gH25N2O10Cl was given to 1 on the basis of the high-resolution fast atom bombardment mass spectral (HRFAB-MS) data.
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