Antimicrobial Activity and Interactions of Toddalia asiatica Isolated Coumarins with Two Known Drugs

Five coumarins namely, 5, 7-dimethoxy-6-(3'-hydroxy-3'-methylbutan-2-oxo) coumarin coumarin (1), Toddalolactone (2), Coumurrenol (3), gleinadiene (4) and Toddaculin (5) were isolated from either the stem and/or root bark of Toddalia asiatica , with compound 1 being reported for the first time. These were obtained using chromatographic methods and identified using spectroscopic techniques, as well as comparison of their physical data with already published results. Combinations of compound 3 and fluconazole displayed additive effect in inhibiting the growth of Penicillium digitatum with reduced MIC to 125 μg/mL compared to that of fluconazole alone at 250 μg /mL. Combination of compounds 1 and 3 also showed additive effect in inhibiting Rhizopus stolonifer lowering the MIC from 500 μg/mL (for both molecules) to 250 μg /mL. Interaction in antibacterial activity between two isolated compounds 1 and 3 was also evident. These lowered the MIC in action against Staphylococcus aureus to 250 μg/mL compared to individual compounds with MIC of 500 μg/mL while showing additive effect. All the crude extracts apart from that of stem bark hexane and the individual isolated compounds showed considerable activity against all the organisms tested.