|Subject||1,1 diphenyl 2 picrylhydrazyl; 1,4 dihydropyridine; 5,6 dihydroazacitidine; 6 hydroxy 2,2,5,7,8 pentamethylchroman; acridan; acridine derivative; antioxidant; calcium channel blocking agent; calcium channel L type; calcium channel L type blocking agent; chain breaking antioxidant; cumene; dibenzo 1,4 dihydropyridine derivative; dihydropyridine derivative; lacidipine; n deuterio 5,6 dihydroazacitidine; n methyl 5,6 dihydroazacitidine; n methyl 9,10 dihydroacridine; nicardipine; peroxy radical; probucol; styrene; trolox C; unclassified drug; antioxidant activity; calcium binding; carbon hydrogen bond dissociation enthalpy; dissociation; enthalpy; hydrogen bond; reaction analysis; reaction optimization; acridines; antioxidants; benzene derivatives; biphenyl compounds; calcium channel blockers; calcium channels, L-type; chromans; dihydropyridines; free radicals; hydrazines; kinetics; nifedipine; nimodipine; oxidation-reduction; peroxides; styrene|
The antioxidant properties of Hantzsch 1,4-dihydropyridine esters and two dibenzo-1,4-dihydropyridines, 9,10-dihydroacridine (DHAC) and N-methyl-9,10-dihydroacridine (N-Me-DHAC), have been explored by determining whether they retard the autoxidation of styrene or cumene at 30 °C. Despite a claim to the contrary [(2003) Chem. Res. Toxicol, 16, 208-215], the Hantsch esters were found to be virtually inactive as chain-breaking antioxidants (CBAs), their reactivity toward peroxyl radicals being some 5 orders of magnitude lower than that of the excellent CBA, 2,2,5,7,8-pentamethyl-6-hydroxy- chroman (PMHC). DHAC was found to be about a factor of 10 less reactive than PMHC. From kinetic measurements using DHAC, N-deuterio-DHAC, and N-Me-DHAC, it is concluded that it is the N-H hydrogen in DHAC that is abstracted by peroxyl radicals, despite the fact that in DHAC the calculated C-H bond dissociation enthalpy (BDE) is about 11 kcal/mol lower than the N-H BDE. The rates of hydrogen atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl radical (dpph.) have also been determined for the same series of compounds. The trends in the peroxyl and dpph. rate constants are similar. © 2006 American Chemical Society.