Synthesis of spirostanol saponins via gold(I)‐catalyzed glycosylation in the presence of Ga(OTf) 3 , In(OTf) 3 , or HOTf
Synthesis of spirostanol saponins via gold(I)‐catalyzed glycosylation in the presence of Ga(OTf) 3 , In(OTf) 3 , or HOTf
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DOI：
10.1002/cjoc.201900126
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发表时间：
2019-08
影响因子：
5.4
通讯作者：
T. Ehianeta;D. Shen;Peng Xu;Biao Yu
中科院分区：
文献类型：
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作者：
T. Ehianeta;D. Shen;Peng Xu;Biao Yu
本文报道了一种依靠Lewis酸或Brønsted酸辅助金(I)催化糖基化的有效方法，合成了一组具有代表性的天然旋香甾醇皂苷，即聚叶毛素D(1)、聚叶毛素V(2)、dioscin(3)、formosanin C(4)和聚叶毛素D的一个末端叠氮基衍生物(5)。这种方法强调了在Ga(OTf)3、in (OTf)3或HOTf （~10mol%）存在的情况下，低负荷的Ph3AuPOTf（≤0.5 mol%）作为共催化剂，在实际反应速率下作为糖基化中传统的~10mol%的金(I)催化剂的替代品。通过六个步骤得到了41%的总产率，而以前使用常规给体和启动子合成的最大产率为30%。通过利用区域选择性鼠李糖基化，采用“一锅”方法组装1和5，从而进一步增强了金(I)‐催化糖基化的效率。
Summary of main observation and conclusionAn effective approach relying on a Lewis acid‐ or Brønsted acid‐assisted gold(I)‐catalyzed glycosylation has been reported in the synthesis of a panel of the representative natural spirostanol saponins, namely polyphyllin D (1), polyphyllin V (2), dioscin (3), formosanin C (4), and a derivative of polyphyllin D bearing a terminal azide group (5). This approach highlights the engagement of low loadings of Ph3AuPOTf (≤ 0.5 mol%) in the presence of Ga(OTf)3, In(OTf)3, or HOTf (~10mol%) as a co‐catalyst, at practical reaction rates as an alternative to the conventional ~10 mol% loadings of the gold(I) catalyst in the glycosylation. Polyphyllin D (1) was obtained in 41% overall yield over six steps compared to the maximum 30% yield in previous syntheses where conventional donors and promoters were used. By exploiting a regioselective rhamnosylation, a “one‐pot” approach was adopted to assemble1and5, thus further strengthening the efficiency of the gold(I)‐catalyzed glycosylation.