Flavonoids from the roots of tephrosia emoroides and their antifeeding effects on the larvae of the spotted stalk borer, Chilo partellus.

Abstract

The thesis describes a chemical and bioactivity study of a tropical plant, Tephrosia emoroides A. Rich. Chromatographic fraction of the petroleum ether and methanol extracts of the roots of the shrub led to the isolation of the flavonoids 5-methoxy isolonchocarpin (1),4",5"-dihydro-5-methxy-5"-isopropeny1furano-[2",3":7,8]-flavonone (2), 7-hydroxy-5-methoxy-8-(3-hydroxy)-isopent-1-eneflavone (3),4",5"-dihydro-5-methoxy-5"-isopropenyi furano-[2",3":7,8]-flav-3-ene (4) and 4',5'-dihydro-isopropenyl-8,9-methylenedioxyfurano-[2',3':2,3]-pterocarpan (5).No previous report has been found in literature on the isolation of the flavanone 3and pterocarpan 5.

Structural elucidation of the compounds was performed on the basis of their spectroscopic data, chemotaxonomic consideration and data correlation. 1H- and 13C-NMR data led to formulation of the molecular structures which were confirmed by the characteristic mass spectral fragmentation patterns. Functional groups were further inferred from the UV and IR data.

The crude petroleum ether extract showed antifeeding activity against the stalk borer Chilo partellus Swinhoe larvae, with mean percentage deterrences of 86.7, 53.4 and 30.0 at doses of 100, 50 and 25 g/disc respectively. Two of the above compounds, 2 and 4 exhibited mild antifeedant activities against the same larvae at different levels of concentrations. For compound 2 the mean percentage deterrences were 66.1, 53.6 and 37.5 at doses of 100, 50 and 25 g/disc respectively. Compound 4 gave mean percentage deterrences of 47.9, 27.4 and 25.0 at similar doses respectively. Antifeedant tests against Chilo partellus larvae were done by choice leaf disc bioassay with Zea mays L. Weighing of the leaf discs left after the experimental period of 24 hours and using an appropriate formula led to the determination of the deterrences.