Alkylating potential of a,b-unsaturated compounds

Abstract

Alkylation reactions of the nucleoside guanosine (Guo) by the alfa,beta-unsaturated compounds (alfa,beta-UC) acrylonitrile (AN), acrylamide (AM), acrylic acid (AA) and acrolein (AC), which can act as alkylating agents of DNA, were investigated kinetically. The following conclusions were drawn: i) The Guo alkylation mechanism by AC is different from those brought about the other alfa,beta-UC; ii) for the first three, the following sequence of alkylating potential was found: AN > AM > AA; iii) A correlation between the chemical reactivity (alkylation rate constants) of AN, AM, and AA and their capacity to form adducts with biomarkers was found. iv) Guo alkylation reactions for AN and AM occur through Michael addition mechanisms, reversible in the first case, and irreversible in the second. The equilibrium constant for the formation of the Guo-AN adduct is Keq (37 °C) = 5 × 10-4; v) The low energy barrier (=10 kJ mol-1) to reverse the Guo alkylation by AN reflects the easy reversibility of this reaction and its possible correction by repair mechanisms; vi) No reaction was observed for AN, AM, and AA at pH < 8.0. In contrast, Guo alkylation by AC was observed under cellular pH conditions. The reaction rate constants for the formation of the alfa-OH-Guo adduct (the most genotoxic isomer), is 1.5-fold faster than that of y-OH-Guo. vii) a correlation between the chemical reactivity of alfa,beta-UC (alkylation rate constants) and mutagenicity was found.