The electrochemical reduction of biotin (vitamin B7) and conversion into its ester

An electrochemical study on biotin (vitamin B7), performed in aprotic solvents and at a platinum electrode, revealed that at approximately Ef0=-1.6 to -1.8 vs. (Fc/Fc⁺)/V (Ef0=formal reduction potential and Fc=ferrocene), biotin is reduced by one-electron to form its carboxylate anion and dihydrogen via a direct discharge of the carboxylic acid at the platinum surface. The electrochemical reduction process appeared to be chemically reversible on the time-frame of cyclic voltammetry (CV) (t ≤ s), but not over the extended period of controlled potential electrolysis (CPE) (t ≥ min) where the conversion of biotin into its carboxylate anion was found to be chemically irreversible. A strategy to functionalize biotin's carboxyl group was established by performing a bulk reductive electrolysis, and then reacting the electrochemically generated carboxylate anion with iodomethane to afford biotin methyl ester in excellent yield (91%). Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was successful in identifying several distinct and characteristic carbonyl absorbance peaks associated with the analogous forms of biotin available before electrolysis, after electrolysis, and after methylation.