Antibiofilm phenylethanoid glycosides from Penstemon centranthifolius.

Bioassay-guided fractionation of the antibacterial ethyl acetate-ethanol (50 : 50) extract obtained from the aerial parts of Penstemon centranthifolius led to the isolation of six phenylethanoid glycosides (1-6) and eleven iridoid glycosides (7-17). Their structures were determined on the basis of spectroscopic analysis and comparison with the literature. Among them, two phenylethanoid glycosides, 4'''-O-acetylverbascoside (1) and verbascoside (2), were found to show significant inhibition of the formation of bacterial biofilms by Escherichia coli UTI89. Compound 1 showed 77% biofilm inhibition at 2.5 microg/mL, and compound 2 showed 60% inhibition at 5 microg/mL.