Voltammetric studies of 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid as a novel prodrug of 5-aminosalicylic acid

The electrochemical properties of a colon-targeted prodrug of 5-aminosalicylic acid (5-ASA), 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid (SPSA), were investigated in aqueous solutions at glassy carbon electrodes using cyclic voltammetry and controlled potential electrolysis. The influence of the pH and experimental time domain on the reaction pathway has been studied. The electrochemical reduction of SPSA is identified as an ECE process always leading to the cleavage of azo bond. In an acidic media SPSA is reduced in a 4e⁻/4H⁺ process yielding 5-ASA and sulfanilic acid. In neutral and weakly basic media SPSA is reduced in 2e⁻/2H⁺ process resulting in the hydrazo intermediate that is stable enough to enable its reoxidation back to SPSA in the time scale of the cyclic voltammetry.