Antibacterial and antifungal activities of different parts of tagetes patula: Preparation of patuletin derivatives

The current study evaluates the antibacterial and antifungal activities of extracts from different parts of Tagetes patula Linn. (Asteraceae), reported for the first time in a single set of experiments. In the preliminary assay, the methanol extract of the flower (JFM) was found to possess antimicrobial activity against a number of bacteria with inhibition zone diameters ranging from 9 to 20 mm, the bioassay-guided fractionation of which led to the isolation of a flavonoid patuletin (3) in high yield as the active antibacterial principle with minimum inhibitory concentration (MIC) value of 12.5 g/disk against Corynebacterium spp., Staphylococcus spp., Streptococcus spp., and Micrococcus luteus. Its glucoside, patulitrin (4), was found to be weakly active, except against Staphylococcus saprophyticus, Streptococcus fecalis, and Streptococcus pyogenes with inhibition zone diameters of 11, 16, and 12 mm, respectively. The cinnamate derivative (3b) of 3 showed antibacterial activity comparable with the parent flavonoid with a MIC value of 50 g/disk against Corynebacterium spp., whereas benzoate derivative (3a) was found to be devoid of any activity; both the derivatives are new compounds. Moreover, the long-chain alcohol 5, which displayed antibacterial activity in the preliminary testing, was obtained in large quantity directly from the petroleum ether extract of the involucre of the flowers.