Chemiluminescent reactions and electrophilic oxygen donating ability of 4a-hydroperoxyflavins: general synthetic method for the preparation of N5-alkyl-1,5-dihydroflavins.

The synthesis of N5-methyl- and N5-ethyl-1,5-dihydroflavin mononucleotides is reported. These compounds show no bioluminescence activity with bacterial luciferase. This feature is interpreted in terms of steric hindrance between the N5-alkyl group and a hydrogen bonding group at the active site of the luciferase. The chemiluminescence observed on reaction of N5-alkyl-1,5-dihydroflavins with oxygen and aldehydes has been shown to occur via formation of a mixed peroxide of flavin and aldehyde and to be associated with a primary deuterium isotope effect when [1-2H]aldehyde is substituted for aldehyde. The time course for light emission has been compared for aldehyde and ketone substrates. The suggestion is entertained that the peroxide bond of 4a-hydroperoxyflavin is sufficiently polarized to allow this species to act as the oxidant per se at the active site of mixed function oxidases. The second-order rate constants for reaction of hydroperoxides with thioxane and I- are compared. 4a-Hydroperoxy-3,5-dimethyllumiflavin is shown to convert thioxane to its sulfoxide 1.8 X 10(5) times faster than t-butyl hydroperoxide.