Acid-Catalyzed E-Ring Expansion and Isomerization of 3-Acetylbetulin: Synthesis of Cytotoxic Anhydrobetulin Saponins |
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Authors: | Dominic Thibeault Jean Legault Charles Gauthier Serge Lavoie Jimmy Bouchard |
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Institution: | Separation and Analysis of Vegetal Products Laboratory, Fundamental Sciences Department , University of Québec at Chicoutimi , Chicoutimi , Québec , Canada |
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Abstract: | 22(17 → 28)abeo-Lupene derivatives 5a and 6a were obtained after the acid-catalyzed E-ring expansion of 3-acetylbetulin (1a). Glycosylation of these dehydrated triterpenoids using Schmidt's trichloroacetimidate sugar donors in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) provided the new anhydrobetulin saponins 7b–7e in which the terminal olefin C-20(29) isomerizes to form a C-19 tetrasubstituted alkene. The preliminary cytotoxic evaluation revealed that saponins 7b–7d exhibited a moderate cytotoxic activity against A549, DLD-1, and WS1 human cell lines with IC50 ranging from 22 to 49 μM. |
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Keywords: | Acid-catalyzed isomerization anhydrobetulin saponins betulin cytotoxicity E-ring expansion triterpenoids |
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