Isolation and characterization of flavanols from Anthocephalus cadamba and evaluation of their antioxidant, antigenotoxic, cytotoxic and COX-2 inhibitory activities

In search of lead molecules for use in disease prevention and as food additive from natural sources, two flavanols were isolated from leaves of Anthocephalus cadamba (Roxb.) Miq., Rubiaceae. Their structures were established as 6-hydroxycoumarin-(4″→8)-(−)-epicatechin and 6-hydroxycoumarin-(4″→8)-(−)-epicatechin-(4→6‴)-(−)-epicatechin on the basis of spectroscopic data. Both the compounds exhibited potent antioxidant and antigenotoxic activity. 6-Hydroxycoumarin-(4″→8)-(−)-epicatechin scavenged DPPH, ABTS+.and superoxide anion radicals with IC50 values of 6.09 μg/ml, 5.95 μg/ml and 42.70 μg/ml respectively whereas the IC50 values for 6-hydroxycoumarin-(4″→8)-(−)-epicatechin-(4→6‴)-(−)-epicatechin were 6.62 μg/ml for DPPH free radicals, 6.93 μg/ml for ABTS radical cations and 49.08 μg/ml for superoxide anion radicals. Both the compounds also exhibited potent reducing potential in reducing power assay and protected the plasmid DNA (pBR322) against the attack of hydroxyl radicals generated by Fenton's reagent in DNA protection assay. In SOS chromotest, 6-hydroxycoumarin-(4″→8)-(−)-epicatechin decreased the induction factor induced by 4NQO (20 μg/ml) and aflatoxin B1 (20 μg/ml) by 31.78% and 65.04% respectively at a concentration of 1000 μg/ml. On the other hand, 6-hydroxycoumarin-(4″→8)-(−)-epicatechin-(4→6‴)-(−)-epicatechin decreased the genotoxicity of these mutagens by 37.11% and 47.05% respectively. It also showed cytotoxicity in COLO-205 cancer cell line with GI50 of 435.71 μg/ml. Both the compounds showed moderate cyclooxygenase-2 inhibitory activity.

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