Studies in the flavin series. Part XVII.

Abstract

The distribution of products from the reductive alkylation of 1,3,7,8-tetramethylalloxazine depends upon whether saturated (hard) or unsaturated (soft) alkylating agents are used. The former yield 5-alkylated 5,10-dihydro-alloxazines and, under more drastic conditions, 5,5-dialkylated derivatives, while the latter (benzyl and allyl bromide) yield 4a-monoalkylated and 4a,5-dialkylated derivatives. The 5-alkyldihydroalloxazines are readily oxidised to the 5-alkylalloxazinium salts, which either undergo hydrolytic dealkylation to the initial alloxazine or, if the 5-substituent is allyl or benzyl, in part rearrange to a 6-alkylalloxazine. Oxygen, under acidic conditions, converts 4a-benzyl-(or allyl)-dihydroalloxazines into the 6-benzyl-(or allyl-)alloxazine via the 5-substituted alloxazinium salt. The mechanisms of these reactions are discussed and their relevance to group transfer reactions of flavocoenzymes is stressed.