Antimicrobial Isoflavans and Other Metabolites of Dalea jamesii

The phytochemical investigation of extracts of Dalea jamesii root and aerial portions led to the isolation of ten phenolic compounds. Six previously undescribed prenylated isoflavans, summarily named ormegans A-F (1-6), were characterized, along with two new arylbenzofurans (7, 8), a known flavone (9), and a known chroman (10). The structures of the new compounds were deduced by NMR spectroscopy, supported by HRESI mass spectrometry. The absolute configurations of 1-6 were determined by circular dichroism spectroscopy. Compounds 1-9 exhibited in vitro antimicrobial activities, causing 98% or greater growth inhibition at concentrations as low as 2.5-5.1 μM against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and Cryptococcus neoformans. Interestingly, the most active compound was the dimeric arylbenzofuran 8 (> 90% growth inhibition at 2.5 μM) against both methicillin-resistant S. aureus and vancomycin-resistant E. faecalis, tenfold more active than its corresponding monomer (7).