Stabile Dihydroflavine und quartäre Flaviniumsalze Studien in der Flavinreihe, 12, Mitteilung

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Abstract
Flavohydroquinones (leucoflavins) protected by acetylation at N(5) have been alkylated to give derivatives substituted at oxygen and/or nitrogen functions in the pyrimidine part of the nucleus. Removal of the protecting group under oxidizing conditions gave N(1),N(3)‐, O(2),N(3)‐ or O(2), O(4)‐dialkyl‐flavoquinonium salts. The N(1)‐substituted type could be reduced to give free flavohydroquinones stable in air, which in turn could be further alkylated at N(5). On oxidation the N(5)‐alkyl groups are readily removed through the radical intermediate. The N(10)‐alkyl groups may be split from the flavoquinonium salt if they are activated (e. g. ‐CH2COOR). The O‐alkyl groups are readily hydrolysed under neutral or slightly acid conditions whereas a basic medium provokes deprotonation at the 8‐CH3 group and concomitant irreversible dimerization. The potential importance of these models for elucidating the mechanism of flavin‐dependent biological dehydrogenation is mentioned.