CHEMICAL CONSTITUENTS AND ANTIOXIDANT ACTIVITY OF Croton megalocarpoides FRIIS & GILBERT AND Physalis angulata LINN.

Abstract

Available drugs used in the treatment of wounds, diabetes, whooping cough, jaundice and ear aches have side effects. Croton megalocarpoides and Physalis angulata are used in ethno-medicine for treatment of these diseases with no scientific proof and there is thus a need to provide scientific based evidence to support the ethno-medicinal uses of these plants. The aim of this study was to isolate and identify phytochemicals responsible for the ethno-medicinal uses of Croton megalocarpoides and Physalis angulata. C. megalocarpoides and P. angulata were collected, identified and authenticated at the herbaria, in the School of Biological Sciences, University of Nairobi, Kenya B/N 2009/08 and Forestry Research Institute of Nigeria, Ibadan FHI 109674, respectively. Pulverised samples of stem bark of C. megalocarpoides and whole plant of P. angulata were macerated with dichloromethane and methanol, respectively. Extracts were screened for the presence of phytochemicals using standard methods. The extracts were further purified using column and flash chromatography. Purified compounds were characterised spectroscopically with Infra-Red (IR), Nuclear Magnetic Resonance (NMR), and Mass Spectroscopic (MS). Extracts and purified compounds were investigated for antioxidant and radical scavenging activities using 2,2-diphenyl-1-picrylhydrazyl (DPPH) at concentration of 1.00-0.06 mg/mL. Data were analysed using descriptive statistics. Dichloromethane extract (7.4 %) of C. megalocarpoides and methanol extract (4.0 %) of P. angulata were obtained. Flavonoid, saponin, terpenoid and tannin were detected in the extract of C. megalocarpoides while alkaloid, saponin, flavonoid, terpenoid and steroid were found to be present in extract of P. angulata. Two new compounds (12-epi-Croton zambefuran A and 1-(p-hydroxy coumaric acid) – geranyl geran-1-ol ) and six known compounds (lupeol, 15,16-epoxy-3,13(16),14-clerodatriene-20,12-olide-18,19-dioic acid dimethyl ester, 18,19-dimethoxy-carbonyl-3αacetoxy,4β-hydroxy-15,16–epoxy-clerodane-7,13(16),14-triene-12,20-olide, 1,2-dehydrocrotocorylifuran–2-one, 7,8-dehydrocrotocorylifuran and lignoceryl-trans-ferulate) were isolated from the extract of C. megalocarpoides. The 12-epi-Croton zambefuran A showed IR absorption band typical of lactone at 1760 cm-1 while the NMR analysis revealed three olefinic signals δH at 6.40, 7.47 and 7.49 ppm and four sp2 carbons at δC 108.4, 125.6 ,139.5 and 144.4 ppm . The MS displayed M+ peak at m/z 423.7 corresponding to the molecular formula C22H24O7. A new squalene derivative (1-hydroxy-squalene) and three known compounds (phytol, squalene and α-tocopherol) were isolated from methanol extract of P. angulata. Croton megalocarpoides and P. angulata extracts exhibited the highest percentage radical scavenging activity at 58.0 and 73.0, respectively. The extracts of C. megalocarpoides and P. angulata showed antioxidant activity with IC50 of 0.79 and 0.06 mg/mL, respectively. The new isolates from both plants showed antioxidant activity with IC50 values ranging from 0.72 to 0.76 mg/mL. Both plants contain phytochemicals that showed antioxidant activity that could be responsible for their ethno-medicinal uses.