Isolation and characterization of antimicrobial compound from the stem-bark of the traditionally used medicinal plant Adenium obesum

BACKGROUND: Medicinal plants constitute a natural reservoir for medicines worldwide. They serve mainstream therapeutics and are central in folklore medicine. In case of Adenium obesum (Lav, Apocynaceae), indigenous people of Oman use it for the treatment of venereal diseases, wounds, skin diseases, headaches, muscle pain as well as joint pain; yet, the active ingredients have not been classified. To screened the antioxidant and antimicrobial activities of an identified compound that we isolated from the highest active chloroform extract. METHODS: The antioxidant and antimicrobial activities of the extracts and the isolated compound were determined by diphenyl-1-picrylhydrazyl (DPPH) and disc diffusion methods. To characterize the compound, we used TLC, column, (1)H-NMR, (13)C-NMR, 2D-NMR, IR and MS. RESULTS: The highest antioxidant activity was found in chloroform extract with EC(50) value of 28.32 μg/ml followed by water, methanol, butanol, ethyl acetate and hexane extracts, their IC(50) being 29.95, 39.17, 42.40, 43.20 and 57.00 μg/ml respectively. All crude extracts and pure compound displayed moderate antimicrobial activity against one Gram positive Staphylococcus aureus and three Gram negative Escherichia coli, Pseudomonas aeruginosa and Proteus vulgaris within growth inhibition range of 0–13 mm. The active metabolite was identified as 3,4-dihydroxycinnamic acid (R)-1-carboxy-2-(3,4-dihydroxyphenyl) ethyl ester which is a common plant ingredient known as rosmarinic acid. CONCLUSION: The results indicate that walnut chloroform fraction may contain effective compounds with a broad spectrum of curative applications. This is the first report on isolation and characterization of a compound from chloroform crude extract of A. obesum.