| Summary: | Five undescribed pentaketide derivatives, (<i>R</i>)-6,8-dihydroxy-4,5-dimethyl-3-methylidene-3,4-dihydro-1<i>H</i>-2-benzopyran-1-one (<b>1</b>), [(3<i>S</i>,4<i>R</i>)-3,8-dihydroxy-6-methoxy-4,5-dimethyl-1-oxo-3,4-dihydro-1<i>H</i>-isochromen-3-yl]methyl acetate (<b>2</b>), (<i>R</i>)-5, 7-dimethoxy-3-((<i>S)</i>-(1-hydroxyethyl)-3,4-dimethylisobenzofuran-1(3<i>H</i>)-one (<b>4b</b>), (<i>S</i>)-7-hydroxy-3-((<i>S</i>)-1-hydroxyethyl)-5-methoxy-3,4-dimethylisobenzofuran 1(3<i>H</i>)-one (<b>5</b>), and a <i>p</i>-hydroxyphenyl-2-pyridone derivative, avellaneanone (<b>6</b>), were isolated together with the previously reported (<i>R</i>)-3-acetyl-7-hydroxy-5-methoxy-3,4-dimethylisobenzofuran-1(3<i>H</i>)-one (<b>3</b>), (<i>R</i>)-7-hydroxy-3-((<i>S</i>)-1-hydroxyethyl)-5-methoxy-3,4-dimethylisobenzofuran-1(3<i>H</i>)-one (<b>4a</b>) and isosclerone (<b>7</b>), from the ethyl acetate extract of a culture of a marine sponge-derived fungus, <i>Hamigera avellanea</i> KUFA0732. The structures of the undescribed compounds were elucidated using 1D and 2D NMR, as well as high-resolution mass spectral analyses. The absolute configurations of the stereogenic carbons in <b>1</b>, <b>4b</b>, <b>5</b>, and <b>6</b> were established by X-ray crystallographic analysis. The absolute configurations of C-3 and C-4 in <b>2</b> were determined by ROESY correlations and on the basis of their common biosynthetic origin with <b>1</b>. The crude fungal extract and the isolated compounds <b>1</b>, <b>3</b>, <b>4b</b>, <b>5</b>, <b>6,</b> and <b>7</b> were assayed for their growth inhibitory activity against various plant pathogenic fungi viz. <i>Alternaria brassicicola</i>, <i>Bipolaris oryzae</i>, <i>Colletotrichum capsici, C. gloeosporiodes</i>, <i>Curvularia oryzae</i>, <i>Fusarium semitectum</i>, <i>Lasiodiplodia theobromae</i>, <i>Phytophthora palmivora</i>, <i>Pyricularia oryzae</i>, <i>Rhizoctonia oryzae</i> and <i>Sclerotium rolfsii</i>.
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