Correlation between Electrochemical and Theoretical Studies on the Leishmanicidal Activity of Twelve Morita-Baylis-Hillman Adducts

Enzymatic bioreduction of nitro groups plays an important role on the activity of biologically active nitroaromatic compounds. Electrochemical methods are useful tools to simulate in vivo metabolic processes. This work presents electrochemical studies in aprotic media (N,N-dimethylformamide (DMF) plus tetrabutylammonium perchlorate (TBAP) 0.1 mol L-1) using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) of twelve Morita-Baylis-Hillman adducts (MBHA) with significant leishmanicidal activity. To facilitate the analysis, the molecules were grouped in four classes according to the side chain. CV studies show three up to four reduction waves, in which the first two waves are related to nitro group reduction. The other waves (presenting more negative potential) refer to the reduction of the alpha,beta-unsaturated carbonyl or to the nitrile activated olefin side-chain. Ortho adducts present facilitated reduction in comparison to the other isomers (meta and para) possibly due to hydrogen bond formation between the benzylic-OH and the nitro group, which stabilizes the reduction product (anion radical nitro) more efficiently than the original compound. Ortho derivatives also present higher leishmanicidal activity upon comparison to the other derivatives of each class. Conformational studies using HF/6-31+G(d)/PCM as a calculation level highlight this effect. Molecular hardness (N) and atomic charges (Q(N)) values corroborate the obtained experimental data.