Antioxidative activity of carbazoles from Murraya koenigii leaves

The antioxidative properties of the leaves extracts of Murraya koenigii usi ng different solvents were evaluated based on the oil stability index (OSI) together with their radical scavenging ability against 1-1-diphenyl-2-picr ylhydrazyl (DPPH). The methylene chloride (CH2Cl2) extract and the ethyl ac etate (EtOAc) soluble fraction of the 70% acetone extract significantly pro longed the OSI values comparable to those of alpha -tocopherol and BHT. Fiv e carbazole alkaloids were isolated from the CH2Cl2 extract and their struc tures were identified to be euchrestine B (1), bismurrayafoline E (2), maha nine (3), mahanimbicine (4), and mahanimbine (5) based on H-1 and C-13 NMR and mass (MS) spectral data. The OSI value of carbazoles at 110 degreesC de creased in the order 1 and 3 > alpha -tocopherol > BHT > 2 > 4, 5 and contr ol. It is' assumed that compounds 1 and 3 contributed to the high OSI. valu e of the CH2Cl2 extract of M. koenigii. The DPPH radical scavenging activit y for these carbazoles-was in the order ascorbic acid > 2 > 1, 3 and alpha -tocopherol > BHT > 4 and 5.