Rearrangement of quinonoid dihydropteridines to 7,8-dihydropteridines

Abstract

The quinonoid isomer of 6,7-dimethyltetrahydropterin has been prepared in situ from the tetrahydropterin by rapid oxidation with potassium ferricyanide. Measurements of the kinetics of the rearrangement of the quinonoid dihydropterin to 7,8-dihydropterin show that the reaction is buffer-catalyzed. Both the acidic and basic forms of the buffer participate as catalysts, with the relative contribution of each species toward the rate of the reaction being dependent on the pKa value of each buffer. Isotopic experiments have shown that the cleavage of the C—H bond at position 6 is rate-limiting during both the acid- and the base-catalyzed rearrangements.