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Revisiting the Cyclocephagenols via Astragalus condensatus: Structural Insights and Configurational Revision
Fadime Aydoğan1, Pankaj Pandey1, Frank R Fronczek2
1National Center for Natural Products Research, School of Pharmacy, University of Mississippi, University, Mississippi 38677, United States.
Abstract:
The phytochemical investigation of the MeOH extract of Astragalus condensatus roots led to the discovery of a new tetrahydropyran cycloartane-type triterpenoid, astracondensatol A (1), alongside six known cyclocephagenol derivatives (2, 3, 20, 32, 35, and 36). Elucidation of their structures involved 1D and 2D-NMR spectroscopy and mass data analysis. Upon comparing NMR spectroscopic data with prior literature, several carbon shift anomalies, particularly at C-24, prompted a reevaluation using quantum chemical calculations, resulting in the revision of the 24S to 24R absolute configuration for compound 2 and 38 other reported cyclocephagenol-type triterpenoids. X-ray crystallography data further supported the analysis in establishing the absolute configuration of compound 2. Ambiguous NOE correlations and publication bias could have played a significant role in miss-assigning the C-24 absolute configuration in tetrahydropyran cycloartane-type triterpenoids.
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