Dihydroflavins alkylation

Finally, the useful subscripts ox and red must be clearly defined as to their correlation either with true redox states or with flavin chromophores. For example, the addition of water to an alkyl-flavo-quinonium ion 5-RFltx 181) leads to a dihydroflavin chromophore, though the redox state did not change The true redox state of 5-RFl-4a-OH formed in this fashion is indicated by the oxygen atom, though it stems from hydroxyl ion. The picture becomes indeterminate in the case of... 

Alkylation Introduction of alkyl groups into the flavin nucleus is a complex matter, which will be extensively reviewed in the dihydroflavin section below. 

N(l) is the site of strongest basicity, but not of strongest nucleo-philicity in the dihydroflavin anion HFEed- This is due to steric hindrance by the peri-substituent at N(10). This hindrance can only be overcome in the case of m/ramolecular N(l)-alkylation, e.g. (66) ... 

Alkyl substituents at N(5) as well as N(l) strongly reduce the 02-affinity of dihydroflavin (see below), while they delete at the same time the long wave end absorption of the Fhed-chromophore 43). 

Photodehydrogenation (or, entirely equivalent to it, photodecarboxylation) follows equation (19), the most common course of flavin photochemistry. It involves a net reduction, yielding free dihydroflavins or alkyl derivatives thereof... 

It may be overlapped by pK s of the substrate ground state, but it is also obtained with entirely non-acidic and non-basic substrates such as benzyl alcohol. Neither starting Flo ground state nor any (alkyl)dihydroflavin products have pK s in this range. Hence, this action pK could reflect the pK of an excited flavoquinone, but since the pK of 1-HFl is around zero and the pK of its excited singlet even lower, the corresponding triplet pK cannot be as high as 5 unless there is a violation of Foerster s rules (J5). 

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