Antioxidant activity of xanthones from stems of Cratoxylum cochinchinense

Abstract

In a search for antioxidant from Thai medicinal herbs, plants in the family Guttifereae were preliminary evaluated using TLC autographic assay with 2,2-Diphenyl-1-picryhydrazyl (DPPH) as a stable radical. The hexane and dichloromethane crude extracts of Cratoxylum cochinchinense were found to have a promising activity. The chromatographic separation of these crude extracts led to the isolation of six new xanthones, cratoxylumxanthone A-F (1,9-11,13-14), along with eigth know xanthones, dulcisxanthone B (2), 2-geranyl-1,3,7-trihydroxy-4-(3-methyl-but-2-enyl)xanthone (3), alpha-mangostin (4), beta-mangostin (5), cochinchinone A (6), garcinone A (7), cochinchinone B (8) and cudratricusxanthone E (12). The structures of all isolated xanthones were characterized by spectroscopic methods as well as comparison with the previous literature data. The antioxidant capability was determined using three complementary in vitro assays, which included the DPPH radical scavenging activity, lipid peroxidation inhibition and xanthine oxidase related activity (superoxide radicals scavenging activity and inhibitory of xanthine oxidase), by comparison with ascorbic acid, curcumin, gallic acid and allopurinol. The three new and three known of isolated xanthones exhibited significant in both DPPH radical scavenging and lipid peroxidation, particularly compound 10 (IC[subscript 50] = 0.030 and 0.013 mM), followed by compound 11(IC[subscript 50] = 0.100 and 0.180 mM), 8 (IC[subscript 50] = 0.120 and 0.130 mM), 13 (IC[subscript 50] = 0.120 และ 0.190 mM) 2 (IC[subscript 50] = 0.140 and 0.040 mM) and 12 (IC[subscript 50] = 0.190 and 0.030 mM), respectively. On the other hand, all isolated xanthones had no effect on superoxide scavenging activity and inhibition of xanthine oxidase activity.