Flavonoids from Pterocaulon alopecuroides with antibacterial activity.

Three flavonoids, (2 R,3 R)-5,4'-dihydroxy-3'- O-methyl-7-(gamma,gamma-dimethylallyloxy)dihydroflavonol 1, (2 R,3 R)-5,7,4'-trihydroxy-3'- O-methyl-6-(alpha,alpha-dimethylallyl)dihydroflavonol 2, and (2 R,3 R)-5,7,4'-trihydroxy-6-(alpha,alpha-dimethylallyl)dihydroflavonol 3, together with three known flavonoids ( 4 - 6), were isolated from the aerial parts of PTEROCAULON ALOPECUROIDES. The structures of the compounds were determined by mass and by 1 D and 2 D NMR spectroscopy. Screening of the antibacterial activity of all six compounds was conducted by a disc diffusion test against BACILLUS CEREUS, BACILLUS SUBTILIS, SALMONELLA TYPHIMURIUM and PROTEUS MIRABILIS. The minimum inhibitory concentration (MIC) of the active compounds ( 2, 3, 4, 6) was determined by a microdilution assay. These compounds were active only against both Gram+ bacteria with MIC values < or = 200 microg/mL.