Alloxazine, methylation

A special influence on the course of a reaction by a neighboring group is shown in the reactions of 5-acetyl-leuco(iso)alloxazines - with diazomethane. The methylation occurs neither in the pyrimidine nor in the pyrazine ring, but on the hydroxyl group of a newly formed oxazoline ring. For example,... 

Using surfactant chromophores, trans-bilayer electron transfer can also be observed, although in the absence of a mediator, the chromophore must be embedded in both surfaces of the bilayer structure. Thus, MV " in the bulk aqueous phase can be reduced by EDTA or sodium ascorbate in the inner water pools if they are separated by a bilayer consisting of 5,10,15-tris(l-methyl-pyridine)-4-yl-20-(4-stearoxyphenyl)porphinatozinc colyophilized with dipalmitoyl-L-phos-phatidylcholine (DPPC). l imilar results are obtained using surfactant derivatives of [Ru(bipy)3] and increased rates of formation are observed if mediators such as hexadecyl-viologen, 2-methyl-1,4-naphthoquinone (vitamin didodecyl- or dibutyl-alloxazine... 

Similarly, condensation of o-phenylenediamine hydrochloride with 1,3-dimethylalloxan gives dimethylalloxazine (14). The latter compound is also obtained by methylation of alloxazine with dimethyl sulfate and alkali together with the methylamide of 3-methylaminoquinoxaline-2-carboxylic acid (15). Prolonged treatment of compounds 14 and IS with 1M sodium hydroxide at 100° yields 3-methylaminoquinoxaline-2-carboxylic acid (16). ... 

The orange chromophore exhibited light sensitivity similar to that of FMN and was degraded to a pale yellow lumichrome analog, which turned orange-red upon deprotonation (pK 6.6). This compound was compared with synthetic 7-methyl-8-hydroxy-alloxazine (17), which in turn was obtained by straightforward condensation of violuric acid with 4-aminocresol in the presence of borate and indeed found to be identical. 

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