Revisiting the Cyclocephagenols via <i>Astragalus condensatus</i>: Structural Insights and Configurational Revision

The phytochemical investigation of the MeOH extract of <i>Astragalus condensatus</i> roots led to the discovery of a new tetrahydropyran cycloartane-type triterpenoid, astracondensatol A (<b>1</b>), alongside six known cyclocephagenol derivatives (<b>2</b>, <b>3</b>, <b>20</b>, <b>32</b>, <b>35</b>, and <b>36</b>). 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 24<i>S</i> to 24<i>R</i> absolute configuration for compound <b>2</b> and 38 other reported cyclocephagenol-type triterpenoids. X-ray crystallography data further supported the analysis in establishing the absolute configuration of compound <b>2</b>. 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.