Electrochemical reduction of azidophenyl-deoxynucleoside conjugates at mercury surface

Azidophenyl-linked nucleotides were previously used for redox-labelling of DNA. Lack of information about electrochemical behavior of aromatic azides in aqueous media and more complex reduction mechanism from to-date presented straightforward two electron reduction to corresponding amines and diatomic nitrogen led us to study the electrochemical reduction process more in detail. Model potassium 4-azidophenyltrifluoroborate (AzPTFB) and the corresponding AzP-linked nucleosides, 7-(4-azidophenyl)-7-deaza-20-deoxyadenosine (dAAzP) and 5-(4-azidophenyl)-20-deoxycytidine (dCAzP), were studied using DC and AC polarography, cyclic voltammetry and electrochemical impedance spectroscopy at dropping mercury electrode or at hanging mercury drop electrode in aqueous buffers. Electrochemical reduction of the azidophenyl conjugates is influenced by pH. Even if electrolysis of AzPTFB and dAAzP at mercury pool confirmed consumption of two electrons per molecule, simple two electron reduction of azide group to amine proceed only in acid electrolytes (pH < 2). Preparative chromatography of the solution obtained after dAAzP electrolysis in ammonium formate-phosphate buffer pH 6.9 and potassium chloride-phosphate buffer pH 6.9 revealed also presence of formylaminophenyl- and phenyl-derivatives. Nevertheless, intermediates such as dimers of the amine compounds and/or hydroxylamine-derivatives, which yield characteristic anodic peak in CV, are transiently formed. The intermediates are finally transformed to amines via reduction at more negative potentials. According to the results, mechanism of dAAzp electrochemical reduction is proposed in this work. (C) 2017 Elsevier Ltd. All rights reserved.