The antioxidative properties of the leaves extracts of Murraya koenigii using different solvents were evaluated based on the oil stability index (OSI) together with their radical scavenging ability against 1-1-diphenyl-2-picrylhydrazyl (DPPH). The methylene chloride (CH(2)Cl(2)) extract and the ethyl acetate (EtOAc) soluble fraction of the 70% acetone extract significantly prolonged the OSI values comparable to those of alpha-tocopherol and BHT. Five carbazole alkaloids were isolated from the CH(2)Cl(2) extract and their structures were identified to be euchrestine B (1), bismurrayafoline E (2), mahanine (3), mahanimbicine (4), and mahanimbine (5) based on (1)H and (13)C NMR and mass (MS) spectral data. The OSI value of carbazoles at 110 degrees C decreased in the order 1 and 3 > alpha-tocopherol > BHT > 2 > 4, 5 and control. It is assumed that compounds 1 and 3 contributed to the high OSI value of the CH(2)Cl(2) extract of M. koenigii. The DPPH radical scavenging activity for these carbazoles was in the order ascorbic acid > 2 > 1, 3 and alpha-tocopherol > BHT > 4 and 5.

A new dimeric carbazole alkaloid, 8,10'-[3,3',11,11'-tetrahydro-9,9'-dihydroxy-3,3',5,8'-tetramethyl-3,3'-bis(4-methyl-3-pentenyl)]bipyrano[3,2-a]carbazole (12), was isolated from the CH(2)Cl(2) extract of Murraya koenigii together with six known carbazole alkaloids, koenimbine (6), O-methylmurrayamine A (7), O-methylmahanine (8), isomahanine (9), bismahanine (10), and bispyrayafoline (11). Their structures were determined on the basis of (1)H and (13)C NMR spectroscopic and mass spectrometric (MS) data. The antioxidative properties of 12 carbazole alkaloids isolated from leaves of M. koenigii were evaluated on the basis of the oil stability index together with their radical scavenging ability against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. On the basis of the lag time to reach a steady state, the 12 carbazoles were classified into three groups. It is suggested that an aryl hydroxyl substituent on the carbazole rings plays a role in stabilizing the thermal oxidation and rate of reaction against DPPH radical.

A model substrate oil using methyl linoleate was established for the determination of the antioxidant activity by Oil Stability Index (OSI) method. OSI values for methyl linoleate with different concentrations (5-100%) in silicone oil were measured at different temperatures (70-120°C). As the temperature increased, the OSI value decreased in each concentration of methyl linoleate. Optimal temperature and concentration of methyl linoleate were established. The effect of concentration of antioxidants, α-tocopherol, and butylated hydroxytoluene on OSI values for 10% methyl linoleate model oil was measured at 90, 100, 110, and 120°C. The logarithmic relationship between temperature and OSI using model substrate oil was similar to that of soybean oil. Furthermore, application of some spice extracts to this model oil system was carried out to give results that compared well with those available in the literature. Thus, the procedure using methyl linoleate-silicone oil as a model substrate oil is available for evaluating the antioxidant activity by the OSI method.The Oil Stability Index analysis method (OSI; AOCS Official Method Cd 12b-92) (1) is one of several methods used to evaluate the stability of fats and oils. It determines stability by measuring conductivity due to volatile organic acids evolved during the oxidation of fats and oils. OSI value is defined as the point of maximal change of the rate of oxidation (1,2). A recently developed oxidative stability instrument allows automatic OSI determinations with a simultaneous analysis of up to 24 samples (3). Although several reports (4,5) showed that there is a close correlation between OSI and the Active Oxygen Method (AOM; AOCS Official Method Cd 12-57) (6), the OSI method has several advantages over the conventional AOM with respect to accuracy and repeatability, and it requires less labor, time, and reagents (2,5). Frankel (7) pointed out the limitations of high-temperature stability tests, such as OSI and AOM in evaluating antioxidants, owing to rapid oxidation, polymerization and cyclization of fats and oils, and decomposition of antioxidants at high temperature. However, antioxidants are commonly used under conditions of high temperature in food processing and cooking. Therefore, it seemed worthwhile to evaluate antioxidative activity at high temperatures by OSI.The OSI method has been used in many studies to evaluate the activity of antioxidants measured in various oils, such as soybean oil (8), lard (9), corn oil (9), whale oil (8), and sardine oil (8). However, the fatty acid compositions of these natural oils vary, which can affect OSI values. Furthermore, these natural oils contain natural antioxidants such as tocopherols which interfere in the determination of the activity of the antioxidants being evaluated. Kajimoto and Murakami (10) revealed that the OSI value of soybean oil stripped of tocopherols decreased as compared with the value of untreated oil. So tocopherols in natural oil had a great influence on the OSI value. Such complications prompted ...

The hetero Diels−Alder reaction of nonactivated conjugated dienes 1 with arylglyoxals 2 and glyoxylate esters 7 proceeded enantioselectively in the presence of a catalytic amount of cationic chiral BINAP−palladium or −platinum complexes and 3 Å molecular sieves (MS3A). The addition of MS3A effectively improved the enantioselectivity of the reaction. Excellent ee's were obtained from the reactions of 2,3-dimethyl-1,3-butadiene (1a) and 1,3-cyclohexadiene (1d) with dienophiles 2 and 7. The square-planar structure of [Pd(S-BINAP)(PhCN)2](PF6)2 was determined by X-ray diffraction, and a chiral induction model involving the square-planar palladium complex coordinated with BINAP and a dienophile is proposed.