Chemical study of Stylosanthes erecta P. Beauv. (Fabaceae)

Stylosanthes erecta P. Beauv. (Fabaceae) is an herbal plant, 20-40 cm height, occurring mainly in West-Africa countries (Mali, Senegal, Nigeria, Congo).1 The decoction of the aerial parts is used in folk Malian medicine, where is known as “segoufali”, for the treatment of urinary and intestinal diseases and particularly against schistosomiasis.2 A study on the characterization of cysteine-proteases in Malian medicinal plants revealed that S. erecta whole plant showed an high papain-like activity3, but, to date, no phytochemical study on this plant is available in the literature. In this work we report the isolation and structural characterization of some new triterpene glycosides from the aerial parts of S. erecta. The dried plant material was finely powdered and exhaustively extracted with solvent at increasing polarity (n-hexane, CHCl3, CHCl3-MeOH 9:1, and MeOH) by maceration at room temperature. A preliminary analysis of the composition in secondary metabolites of each extract was obtained by LC-ESI-MS. Successively, the purification of the residues was accomplished by different chromatographic techniques such as Sephadex LH-20, silica gel column, and HPLC. The structural elucidation of pure compounds was achieved by extensive spectroscopic methods including 1D- (1H, 13C, 13C DEPT, TOCSY, ROESY) and 2D-NMR experiments (DQF-COSY, HSQC, HMBC), as well as ESI-MS analysis. Compounds belonging to different classes of secondary metabolites such as flavonols, both aglycons and glycosides, phenylpropanoid derivatives, and triterpene derivatives were identified. Among these constituents, triterpene glycosides were the new natural products, characterized by 3,22-dihydroxy-olean-12-en-16-one as aglycon, which was also never described before.