A new flavonol derivative and other compounds from the leaves of Schum with activity against multidrug-resistant bacteria.

Investigation of the leaves of Schum led to the isolation and identification of a new flavonol derivative, 6-C-methylquercetin-3,4'-dimethyl ether () together with eleven known compounds (-), with two of them ( and ) obtained as a mixture. Their structures were established by extensive spectroscopic analyses. Antibacterial activity of compound as well as the reference antibiotic, ciprofloxacin was tested on Gram-negative multidrug-resistant bacteria overexpressing active efflux pumps, and against methicillin-resistant strains of (MRSA). Samples were tested alone and in combination with an efflux pump inhibitor (EPI), phenylalanine-arginine--naphthylamide (PAßN). Results show that when compound was tested alone, its inhibitory effects were obtained on 7/10 tested bacteria with the highest MIC value of 128 µg/mL whilst in the presence of EPI, this activity significantly increase in all the 10 bacteria. An interesting antibacterial activity was obtained with compound against ATCC11296 (MIC of 4 µg/mL), KP55 and MRSA6 in the presence of the PaßN.