Phytochemical Investigation of the Stem Bark of Tephrosia aequilata

The genus Tephrosia of the family Leguminoseae subfamily Papilinodenae is known to be rich in flavonoids and isoflavonoids with diverse biological activities including antimicrobial, antiplasmodial and antioxidant properties. In this research project the air dried stem of Tephrosia aequilata was extracted using dichloromethane/methanol (1:1) by cold percolation for 72 hours at room temperature. The crude extract showed a rich profile of compounds using thin layer chromatography (TLC) analysis. The extract was subjected to a combination of chromatographic separation and purification techniques which led to the isolation of six pure compounds. The compounds were analysed by one dimensional (1H and 13C NMR) and two dimensional (COSY, HSQC and HMBC) NMR analyses. Interpretation of the spectra led to the characterization of the compounds as three chalcones: E-praecansone A, (1) Z-praecansone A, (2) pracansone B (3); two flavanone: obvatin (4) and, candidone (5), and a pterocarpan: 6-hydroxy-3,4:8,9- dimethylenedioxypterocarpan (6). This is the first report on the occurrence of compounds 3-6 in Tephrosia aequilata.

Spectral analysis and comparison with literature suggested that the 8, 9-(Z) isomer of praecansone A converts to the 8, 9-(E) isomer on standing. This phenomena has not been reported for this species.           

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