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Antimicrobial and Antiinsectan Phenolic Metabolites of Dalea searlsiae

Belofsky, Gil, Aronica, Mario, Foss, Eric, Diamond, Jane, Santana, Felipe, Darley, Jacob, Dowd, Patrick F., Coleman, Christina M., Ferreira, Daneel
Journal of natural products 2014 v.77 no.5 pp. 1140
Bacillus cereus, Dalea, Spodoptera frugiperda, Staphylococcus aureus, Streptococcus mutans, antibacterial properties, bioassays, chemical structure, chromatography, circular dichroism spectroscopy, flavanones, fractionation, indigenous species, larval development, metabolites, methanol, mortality, nuclear magnetic resonance spectroscopy, pests, roots, rotenoids, Western United States
Continued interest in the chemistry of Dalea spp. (Fabaceae) has led to investigation of Dalea searlsiae, a plant native to areas of the western United States. Methanol extractions of D. searlsiae roots, and subsequent chromatographic fractionation, afforded the new prenylated and geranylated flavanones, malheurans A-D (1-4), and known flavanones (5-6). Known rotenoids (7,8) and isoflavones (9,10) were isolated from aerial portions. Structure determination of pure compounds was accomplished primarily by extensive 1D and 2D NMR spectroscopy. The absolute configuration of compounds 1-5, 7, and 8 was assigned using electronic circular dichroism spectroscopy. Antimicrobial bioassays revealed significant activity concentrated in the plant roots. Compounds 1-6 exhibited MICs of 2-8 µg/mL against Streptococcus mutans, Bacillus cereus, and oxacillin-sensitive and resistant Staphylococcus aureus. Aerial metabolites 7-10 were inactive against these organisms, but the presence of 7 and 8 prompted investigation of the antiinsectan activity of D. searlsiae metabolites toward the major crop pest Spodoptera frugiperda (Fall Armyworm). While compounds 1-10 all caused significant reductions in larval growth rates, associated mortality (33-66%) was highest with flavanone 4, and rotenoids 7 and 8. These findings suggest a differential allocation of antimicrobial and antiinsectan plant resources to the root and aerial portions of the plant, respectively.