Abstract
The macrofilaricidal property of the plant, Plumbago indica/rosea, was investigated in vitro against Setaria digitata, a filarial parasite of cattle. Adult worms were incubated in a medium containing crude extract at concentrations 0.05, 0.04, 0.02, and 0.01 mg mL^−1^ for various incubation periods of 30 min, 1 h, 2 h, and 6 h, respectively, at 37°C and the worm motility was compared with that of solvent control worms kept in drug‐free medium. Complete inhibition of motility was observed for concentrations ranging from 0.02 to 0.05 mg mL^−1^, whereas in the control all the worms were active. Bioassay‐guided fractionation of the crude extract by silica gel column chromatography resulted in the identification of a very active fraction. The activity of this fraction against adult worms was further confirmed by 3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyl tetrazolium bromide–formazan colorimetric assay, which gave >50% inhibition for the active fraction at concentrations 0.05, 0.002, 0.005, and 0.0006 mg mL^−1^ at 30 min, 1 h, 2 h, and 6 h incubation periods, respectively. The physical and chemical data obtained from melting point determination, thin‐layer chromatography and high‐performance liquid chromatography analysis and IR, ^1^HNMR, ^13^CNMR, and gas chromatography‐mass spectrometry spectral analysis have indicated the chemical structure of the active molecule as 5‐hydroxy‐2‐methyl‐1,4‐naphthalenedione (plumbagin). Drug Dev. Res. 56:33–39, 2002. © 2002 Wiley‐Liss, Inc.