Chemical Synthesis and Some Properties of 6-Substituted Flavins

A number of derivatives of riboflavin and of 3-methyllumiflavin substituted in the 6 position have been synthesized starting with 6-nitro flavins, reduction to the 6-amino flavin, and diazotization, followed by reaction with the appropriate nucleophile. The absorption spectra, oxidationreduction potentials, and the electron spin resonance spectra of the radical cationic forms of several of these synthetic compounds have been determined, including 6-S-cysteinyl-3methyllumiflavin and 6-S-cysteinylriboflavin. The latter has been shown to be identical with the dephosphorylated form of the aminoacyl flavin isolated from trimethylamine dehydrogenase [Steenkamp, D. l., Kenney, W. c., & Singer, T. P. (1978) J. BioI. Chem. 253, 2812-2817; Steenkamp, D. l., McIntire, W., & Kenney, W. C. (1978) J. BioI. Chem. 253, 2818-2824] in regard to absorption spectrum, photochemical properties, and mobility in high-voltage electrophoresis and in thin-layer chromatography. An unusually pronounced interaction between the amino group and the isoalloxazine ring system was deduced from the absorption spectra of 6-amino-3-methyllumiflavin and 6-aminoriboflavin