Antimicrobial Activity ofColeus forskohlii Fractions, Isolation and Characterization of Phenolic Compounds

Abstract

Background: It is known that medicinal plants represent promising candidates against many species of pathogenic bacteria. The south area of Saudi Arabia “Asir region” has a unique habitat and its medicinal plant's composition is still nearly unexplored. Therefore, the aim of the present work is to investigate the antimicrobial activities of Coleus forskohlii fractions and to identify the major active compounds. Methods: The total plant extract was partitioned by petroleum ether, ethyl acetate and n-butanol. Agar well diffusion was assessed to evaluate the antimicrobial activities of the plant fractions against Gram-positive, Gram-negative and Candida albicans. Successive column chromatography was performed to isolate the major metabolites. Structures of the isolated compounds were determined by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. Results: All plant fractions showed significant antimicrobial potential activities against the tested pathogens, where ethyl acetate exhibited the highest antimicrobial activity, followed by petroleum ether then n-butanol. From the n-butanol fraction, thymoquinol-2-O-β-glucopyranoside (1) was isolated while syringic acid (2), methyl 3,4,5-trihydroxybenzoate (3), and luteolin (4) were assigned from the ethyl acetate fraction. Conclusion: The antimicrobial assays revealed that ethyl acetate was the most potent fraction and the major abundant metabolites of C. forskohlii, thymoquinol-2-O-β-glucopyranoside (1), syringic acid (2), methyl 3,4,5-trihydroxybenzoate (3), and luteolin (4) were isolated herein for the first time.