Etude chimique de deux plantes médicinales camerounaises, Indigofera atriceps et Indigofera spicata (Fabaceae) et évaluation des activités antibactériennes et inhibitrices de l’Urease des composés isolés.

Abstract

The present work deals with the extraction, isolation, purification, structural elucidation and evaluation of antimicrobial activities and inhibitory activities against urease of secondary metabolites isolated from two Cameroonian medicinal plants, Indigofera atriceps and Indigofera spicata (Fabaceae). From the CH2Cl2/CH3OH (1:1) extracts of the whole plants, we isolated and purified 21 compounds by the application of liquid phase chromatographic methods such as Flash Chromatography, Column Chromatography (CC) and analytical and preparative Thin Layer Chromatographies (TLC). These compounds were distributed into nine families including: - Three benzoic acids among which one new derivative named atricephenol A and two known derivatives identified as p-hydroxybenzaldehyd and dipentyl phtalate; - One new stilbenoid named atricephenol B; - Two benzofurans of which one new derivative named spibenzofuran, and one known derivative namely 2-(2′-hydroxy-4′-methoxyphenyl)-5,6-methylenedioxybenzofuran; - Five known flavonoïds identified as genistein, (-)-melilotocarpan A, (-)-melilotocarpan D, maackiain and 7,3'-dihydroxy-6,4'-dimethoxyflavon; - One known cyclic polyol named bornesitol; - One known saponin identified as soyasaponin I; - Four known steroids including β-sitostérol, stigmasterol, sitosterol-3-O-β-D-glucopyranoside and stigmasterol-3-O-β-D-glucopyranoside. - Two known triterpens namely lupeol and betulenic acid; - Two known fatty acids including behenic acid and Eicosanoic acid n-butyl ester. The structures of these compounds were determined by usual spectroscopic methods (UV, IR, CD, MS, NMR 1H and 13C, HSQC, HMBC, COSY and NOESY), identification tests or comparison of their spectroscopic data with those reported in literature. The antimicrobial and urease inhibitory activities tests were performed on compounds isolated from both plants. Concerning antimicrobial activities, they were evaluated, by an agar diffusion assay and compared with streptomycin, on six straims namely Pseudomonas aeruginosa; Escherichia coli; Salmonella typhi; Klebsiella pneumonia; Streptococcus faecalis; and Micrococcus sp. The results showed that, only soyasaponin I exhibited significant activity against 3 different strains: Salmonella typhi (ZI=13 mm), Streptococcus faecalis (ZI=14 mm) and Micrococcus sp. (ZI=16 mm). Other compounds such as maackiain sitol showed significant activity against Escherichia coli (ZI=13 and 15 mm respectively). Concerning urease inhibitory properties, they were determined by using the indophenol method, as previously described by Weatherburn in 1967 and thiourea was used as the standard inhibitor of urease. The results showed that, β-sitosterol and bornesitol displayed greater activity than that of the standard (Thiourea with IC50 value of 21.5 μg/mL) with IC50 values of 18.6 and 19.3 μg/mL respectively. However, Genistein and soyasaponin I showed significant activity with IC50 values of 28.9 and 23.6 μg/mL respectively.