Comparison of the electrochemical properties of some colon-specific prodrugs of mesalazine.

The electrochemical behavior of 2-hydroxy-5-[(4-sulfophenyl)azo]benzoic acid, 2-hydroxy-5-[(3-sulfophenyl)azo]benzoic acid and 2-hydroxy-5-[(2-sulfophenyl)-azo]benzoic acid was investigated by cyclic voltammetry using a glassy carbon electrode. The influence of the pH and position of the substituents on the reaction pathway has been studied. The results obtained are compared to the electrochemical properties of olsalazine. The reduction of these compounds is identified as an ECE process always leading to the cleavage of the azo bond. The electron-donating hydroxyl group in para position with respect to the azo bridge weakens the N-N bond, whereas the presence of the sulfo group strengthens this bond and renders the hydrazo intermediate more stable comparing to the hydrazo derivatives with two electron-donating groups in para positions.