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The chemical investigation of a methanol extract of the deep-sea-derived fungus <i>Diaporthe longicolla</i> FS429 led to the isolation of two novel diterpenoids longidiacids A and B (<b>1</b> and <b>2</b>), two new polyketides (<b>3</b> and <b>4</b>), two new cytochalasin analogues longichalasins A and B (<b>6</b> and <b>8</b>) and three known analogues <b>5</b>, <b>7</b>, <b>9</b>. Their structures were elucidated through comprehensive spectroscopic analysis, while the absolute configurations were established by the comparison of the experimental and quantum chemical calculated ECD spectra. The structure of compound <b>7</b> was confirmed through X-ray diffraction for the first time. In the bioassays compound <b>8</b> exhibited antiproliferative effects against SF-268, with an IC₅₀ value of 16.44 μM. Moreover, compounds <b>1</b> and <b>8</b> were detected to inhibit 35.4% and 53.5% of enzyme activity of <i>Mycobacterium tuberculosis</i> protein tyrosine phosphatase B (<i>M</i>ptpB) at a concentration of 50 μM.