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

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Abstract
The synthesis of N5-methyl- and N5-ethyl-1,5-dihydroflavin mononucleotides is reported. These compounds show no bioluminescence activity with bacterial luciferase [Photobacterum fischeri and Beneckea harveyi]. This feature is interpreted in terms of steric hindrance between the N5-alkyl group and H-bonding group at the active site of the luciferase. The chemiluminescence observed on reaction of N5-alkyl-1,5-dihydroflavins with O2 and aldehydes occurs via formation of a mixed peroxide of flavin and aldehyde and associated with a primary deuterium isotope effect when [1-2H]aldehyde is substituted for aldehyde. The time course for light emission was compared for aldehyde and ketone substrates. The peroxide bond of 4a-hydroperoxyflavin may be sufficiently polarized to allow this species to act as the oxidant per se at the active site of mixed function oxidases. The 2nd-order rate constants for reaction of hydroperoxides with thioxane and I- are compared. 4a-Hydroperoxy-3,5-dimethyllumiflavin converts thioxane to its sulfoxide 1.8 .times. 105 times faster than tert-butyl hydroperoxide.

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