Mechanism and products of electrochemical reduction of 4-(nitrophenyl) substituted 1,4-dihydropyridines

An electrochemical evidence of free radicals formation from flutamide and its reactivity with endo/xenobiotics of pharmacological relevance

This paper reports the feasibility of free radicals formation from flutamide by using cyclic voltammetry. The electrochemical characteristics and the reactivity of the one-electron reduction product from flutamide in mixed media with thiol compounds and the nuclei acid bases are characterized. Results from this paper show the thermodynamic feasibility of free radical formation expressed for both the cathodic peak potential and the second-order rate constant values. The reactivity of the radical towards thiol compounds (glutathione, cysteamine, N-acetylcysteine) and the nuclei acid base, adenine, thymine and uracil were quantitatively assessed through the calculation of the respective interaction rate constants. Based on these results, the following tentative order of reactivity towards the xeno/endobiotics is as follows: cysteamine > uracil > glutathione > adenine > N-acetylcysteine > thymine. The stability of the nitro radical anion electrochemically generated from flutamide showed a linear dependence with pH.

Electrochemical generation and reactivity of free radical redox intermediates from ortho- and meta-nitro substituted 1,4-dihydropyridines

This paper reports a comprehensive study by cyclic voltammetry on the electrochemical characteristics and the reactivity of the one-electron reduction product from a series of nitro aryl 1,4-dihydropyridines in mixed and aprotic media. In addition, the effects of 1,4-DHP on the oxygen consumption of T. cruzi epimastigotes are reported. One-electron reduction products from 1,4-DHP derivatives significantly reacted with both thiol compounds and the nuclei acid bases, adenine and uracil. This reactivity was significantly higher than the natural decay of the radicals in mixed media. Based on these results the following tentative order of reactivity towards the xeno/endobiotics is as follows: cysteamine > glutathione > adenineuracil. Both the stability and the reactivity of the nitro radical anions electrochemically generated from 1,4-DHP showed a linear dependence with pH. The sensitivity to pH of the radicals derived from o-nitro substituted derivatives was significantly higher than m-nitro substituted derivatives. On the other hand, in all cases an increase of pH produced a significant decrease in the interaction rate constant. Interaction studies carried out in aprotic media did not show any reactivity of the radicals towards both thiol compounds and the nuclei acid bases, adenine and uracil. Therefore, we concluded that the interaction process requires certain proton activity in the media. All the tested 1,4-dihydropyridines inhibited the oxygen consumption by T. cruzi epimastigotes, Tulahuén strain. The drugs with higher electron-affinity produced greater inhibition than those with lower electron-affinity (i.e. nicardipine vs nifedipine).

Adsorptive stripping voltammetry of nicardipine at a HMDE; determination of trace levels nicardipine in blood and urine

The redox behaviour of nicardipine, a 1,4-dihydropyridine calcium antagonist, has been studied in different media on mercury, glassy carbon, gold and platinum electrodes using various voltammetric techniques. A highly sensitive adsorptive stripping voltammetric method for the determination of nicardipine based on adsorption of the drug onto mercury, followed by differential pulse voltammetric determination of the surface species, is described. All factors (pH, supporting electrolyte, accumulation potential and time, etc.) influencing adsorption as well as voltammetric response are discussed. The application of adsorptive stripping voltammetry at the hanging mercury drop electrode (HMDE) to the determination of trace levels of nicardipine in human urine and blood is illustrated, without an extraction procedure being necessary prior to the voltammetric measurement. A limit of detection of 4.8 ng per ml urine and 34 ng per ml blood is found with a mean recovery of nicardipine in urine and blood of 97%. The mean relative error does not exceed 6.5%.