title: Mechanism of biochemical action of substituted 4-methylbenzopyran-2-ones. Part 5: Pulse radiolysis studies on the antioxidant action of 7,8-diacetoxy-4-methylcoumarin.
abstract: 7,8-Dihydroxy-4-methylcoumarin (1, DHMC) and 7,8-diacetoxy-4-methylcoumarin (2, DAMC) were shown to possess radical scavenging property and strongly inhibit membrane lipid peroxidation. Although free polyphenolic compounds are known to be antioxidants, the antioxidant action of the acetoxy compound DAMC was intriguing. Hence, pulse radiolysis studies were undertaken to explain the antioxidant action of DAMC. Accordingly, DAMC and DHMC were separately reacted with the system generating azide radicals and the resulting transient spectra were recorded. The spectra so obtained in both the cases demonstrated peak at 410 nm, characteristic of phenoxyl radical. The rate constants for the formation of phenoxyl radical from DHMC and DAMC were 34 x 10(8) M(-1) s(-1) and 6.2 x 10(8) M(-1) s(-1), respectively. We propose that the free radical mediated oxidation of DAMC initially produces a radical cation that loses an acetyl carbocation to yield the phenoxyl radical. It is possible to conclude that the mechanism of the antioxidant action of DAMC follows the pathway similar to that of DHMC involving the formation of a stable phenoxyl radical.
authors.affiliation: Department of Biochemistry, VP Chest Institute, University of Delhi, India.
authors.forename: H G
authors.initials: HG
authors.lastname: Raj
authors.forename: V S
authors.initials: VS
authors.lastname: Parmar
authors.forename: S C
authors.initials: SC
authors.lastname: Jain
authors.forename: K I
authors.initials: KI
authors.lastname: Priyadarsini
authors.forename: J P
authors.initials: JP
authors.lastname: Mittal
authors.forename: S
authors.initials: S
authors.lastname: Goel
authors.forename: S K
authors.initials: SK
authors.lastname: Das
authors.forename: S K
authors.initials: SK
authors.lastname: Sharma
authors.forename: C E
authors.initials: CE
authors.lastname: Olsen
authors.forename: J
authors.initials: J
authors.lastname: Wengel
mesh_terms: D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D003374:Coumarins / Q000737:chemistry / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000737:chemistry / Q000494:pharmacology; D010084:Oxidation-Reduction; D011675:Pulse Radiolysis; D011714:Pyrans / Q000737:chemistry / Q000494:pharmacology*; D013481:Superoxides / Q000737:chemistry
chemical_list: C114369:7,8-diacetoxy-4-methylcoumarin; D000975:Antioxidants; D003374:Coumarins; D016166:Free Radical Scavengers; D011714:Pyrans; D013481:Superoxides