Synthesis of betavulgaroside III, a representative triterpene seco-glycoside |
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Authors: | Zhu Shilei Li Yingxia Yu Biao |
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Institution: | Key Laboratory of Marine Drugs, Marine Drug and Food Institute, Ocean University of China, Qingdao 266003, China. |
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Abstract: | Triterpene seco-glycosides constitute a small family of the plant saponins which feature a terminal seco-saccharide appendage deriving supposedly from oxidative scission of a monosaccharide unit. Herein, we have developed synthetic approaches for the first time to the access to these molecules. Betavulgaroside III (1), a representative congener occurring in Beta vulgaris and Achyranthes fauriei, is successfully synthesized in a total of 31 steps with L-arabinose, D-glucose, and oleanolic acid as starting materials. The longest linear sequence requires 23 steps and in an overall 0.9% yield (from D-glucose). The synthesis features oxidative elaboration of the seco-saccharide unit prior to assembly of the triterpene 3,28-bisglycoside. This tactic has been proven superior, in the attempts to the synthesis of the more easily accessible 2'-epi-betavulgaroside III (2), to that employing oxidative cleavage of the terminal saccharide unit at an advanced triterpene 3,28-bisglycoside scaffold. |
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