8-Fluoro-8-demethylriboflavin as a potential active-site-directed reagent for flavoprotein. Reaction with some amino acids.

8-Fluoro-8-demethylriboflavin was shown to be a potential active-site-directed reagent for flavoproteins. It reacted with the nucleophiles of N-acetylcysteine (-SH), N-acetyltyrosine (-OH), alpha-N-acetyllysine, and glycine (epsilon- and alpha-NH2, respectively) under fairly mild conditions, and the reaction products were identified. The reactivity of the fluoroflavin was higher than that of 8-chloro-8-demethylriboflavin, which reacted only with the cysteine derivative among the amino acid derivatives used, and whose pseudo first order rate constant at 23 degrees C was 1/23 of that of the fluoroflavin. The reactivity of the fluoroflavin was also estimated by 13C and 19F NMR spectroscopy. The results showed that this compound is more reactive than the chloroflavin.