Bioassay-Guided Isolation of New Flavonoid Glycosides from Platanus × acerifolia Leaves and Their Staphylococcus aureus Inhibitory Effects

Despite the rapid advances in drug R&D, there is still a huge need for antibacterial medications, specifically for the methicillin-resistant Staphylococcus aureus (MRSA). Inspired by the research where a viable class of MRSA inhibitors was found in the species Platanus occidentalis, a S. aureus inhibition screening-guided phytochemical reinvestigation on Platanus × acerifolia (London plane tree) leaves were performed with four flavonoid glycosides garnered, including two new compounds, quercetin-3-O-α-l-(2″-E-p-coumaroyl-3″-Z-p-coumaroyl)-rhamnopyranoside (E,Z-3′-hydroxyplatanoside, 1) and quercetin-3-O-α-l-(2″-Z-p-coumaroyl-3″-E-p-coumaroyl)-rhamnopyranoside (Z,E-3′-hydroxyplatanoside, 2). All of the isolates showed significant S. aureus ATCC 25904 inhibitory activity with MICs ranging from 4 to 64 μg/mL, suggesting the potential of discovering drug leads for the control of S. aureus from such a rich, urban landscaping plant in the Platanus genus.