Xanthones are compounds with a diphenyl ether skeleton mainly found in plants and often glycosylated at carbon atoms. Although many C-glycosyltransferases (CGTs) participating in flavone C-glycosylation have been identified, MiCGT from Mangifera indica, adding sugar to an open-chain benzophenone skeleton, is the only identified xanthone biosynthesis-related CGT. Here, we identified two CGTs from Hypericum perforatum that add sugar to the closed-ring xanthone, but not benzophenone. These CGTs catalyze sugar transfer to the C-4 position of norathyriol (1,3,6,7-tetrahydroxyxanthone) to form isomangiferin (1,3,6,7-tetrahydroxyxanthone 4-C-glucoside), a major xanthone C-glucoside. This is the first study to report CGTs that mediate the direct C-glycosylation of xanthone.

中文翻译：

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在贯叶连翘中催化直接呫吨酮 4-C-糖基化的糖基转移酶的鉴定和表征

氧杂蒽酮是具有二苯醚骨架的化合物，主要存在于植物中，通常在碳原子上进行糖基化。尽管已经鉴定了许多参与黄酮C-糖基化的C-糖基转移酶 (CGT) ，但来自籼稻的MiCGT ，将糖添加到开链二苯甲酮骨架，是唯一确定的与呫吨酮生物合成相关的 CGT。在这里，我们确定了来自贯叶连翘的两种 CGT，它们将糖添加到闭环氧杂蒽酮，但不添加二苯甲酮。这些 CGT 催化糖转移到正四醇（1,3,6,7-四羟基呫吨酮）的 C-4 位，形成异芒果苷（1,3,6,7-四羟基呫吨酮4- C-葡萄糖苷），一种主要的呫吨酮C-葡萄糖苷。这是第一项报道介导氧杂蒽酮直接C-糖基化的CGT 的研究。