Location: Crop Bioprotection ResearchTitle: Antimicrobial and antiinsectan phenolic metabolites of dalea searlsiae Author
Submitted to: Journal of Natural Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2014
Publication Date: 4/25/2014
Publication URL: http://handle.nal.usda.gov/10113/60575
Citation: Belofsky, G., Aronica, M., Foss, E., Diamond, J., Santana, F., Darley, J., Dowd, P.F., Coleman, C., Ferreira, D. 2014. Antimicrobial and antiinsectan phenolic metabolites of Dalea searlsiae. Journal of Natural Products. 77(5):1140-1149. Interpretive Summary: Insects cause billions of dollars of crop losses each year and can also facilitate the infestation of molds that make toxins and carcinogens in corn and other crops. Determining the insect resistance mechanisms in wild plants can help with the search for new or lost resistance mechanisms in crop plants. A series of compounds was isolated from rangeland plants, and some were found to have activity against corn insect pests, as well as some human pathogens. Portions of the presumed biosynthetic pathways for these compounds also occur in corn and other crop plants. Provided further environmental tests prove favorable, these compounds may have use as naturally-derived insecticides, and genes responsible for their biosynthesis could be introduced into corn or other crops, thereby reducing insect damage and enhancing the potential for sustainable production of healthier crops for consumers, animals and end users.
Technical Abstract: 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.