Antimicrobial flavanones and other metabolites of Dalea albiflora

The chemically prolific plant genus Dalea has afforded metabolites that are diverse in both structure and biomedically relevant activities. Investigation of Dalea albiflora, native to the Southwestern United States, has led to the isolation of three previously undescribed prenylated flavanones, albiflorans A-C (1-3). Compound structures were deduced by 1D and ²D NMR spectroscopic methods and supported by high resolution mass spectrometry. The absolute configurations of 1-3 were established by circular dichroism spectroscopy. Polarimetry was used to confirm the absolute configurations of the previously described flavanones 4-6, and pterocarpans 7-9. All isolates were tested for antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VRE), Cryptococcus neoformans, and Candida albicans. Albifloran A (1) exhibited antibacterial activity against MRSA and VRE, with MIC values of 1.9 μM and 2.3 μM, respectively. It was also the most potent compound toward C. neoformans with an MIC of 3.3 μM. Albifloran C (3) and the previously described flavanones 4-6 exhibited MICs ranging from 1.7 to 11.5 μM against MRSA and VRE. Flavanone 5 was the most inhibitory compound in the series toward C. albicans with an MIC of 6.4 μM. This study adds to the growing body of knowledge of the metabolites of Dalea spp. and to speculation regarding their structure-activity relationships.