Cladoxanthones A and B, Xanthone-Derived Metabolites with a Spiro[cyclopentane-1,2′-[3,9a]ethanoxanthene]-2,4′,9′,11′-tetraone Skeleton from a <i>Cladosporium</i> sp.

Cladoxanthones A (1) and B (2), two xanthone-derived metabolites featuring a new spiro­[cyclopentane-1,2′-[3,9a]­ethanoxanthene]-2,4′,9′,11′(4a′H)-tetraone skeleton, were isolated from cultures of the ascomycete fungus Cladosporium sp., together with the known mangrovamide J (3). Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 and 2 were assigned by X-ray crystallography using Cu Kα radiation. Compound 1 could be generated from the hypothetical precursors related to α-methylene ketone and dihydro-xanthone via a Diels–Alder reaction, while 2 could be an oxidative coupling product resulting from 1 and 3. Compounds 1 and 2 showed weakly cytotoxic effects.从子囊菌枝孢霉属未定种（Cladosporium sp.）的发酵培养物中，分离得到两个带有新型螺[环戊烷-1,2′-[3,9a]乙撑氧杂蒽]-2,4′,9′,11′(4a′H)-四酮骨架的氧杂蒽酮类衍生代谢物克拉多占吨酮A（Cladoxanthones A）(1)与克拉多占吨酮B（Cladoxanthones B）(2)，同时还获得了已知化合物红树林酰胺J（mangrovamide J）(3)。其结构主要通过核磁共振（NMR）实验进行解析。化合物1和2的绝对构型通过采用Cu Kα辐射的X射线晶体衍射法予以确定。推测化合物1可由与α-亚甲基酮和二氢氧杂蒽酮相关的假想前体经狄尔斯-阿尔德（Diels–Alder）反应生成，而化合物2则可能是由1与3经氧化偶联反应得到的产物。化合物1和2均表现出较弱的细胞毒性活性。