Chemical processes that can damage cellular DNAReactivity and alkylating potential of some O-heterocycles

Resumo

Alylating agents are archetypical carcinogens, since they are able to form covalent links with DNA. Many heterocycles, given their strained rings, are potent electrophiles that undergo ring-opening reactions with biological nucleophiles. In this work, the relationships among the general chemical reactivity, the ring-opening reactions, the ability to alkylate DNA and the biological effects of a series of O-heterocycles have been researched. Compounds investigated include lactones (especially beta-lactones such as diketene), oxetanes and halohydroxifuranones, including powerful mutagen MX and mucohalic acids. Reaction mechanisms were investigated kinetically: alkylation reactions were studied using a nucleophilicity probe for DNA (4-(p-nitrobenzyl)pyridine, NBP) and hydrolysis reactions were studied using UV-Vis spectroscopy and automated titration. Equilibrium constants were determined using spectroscopic measurements (UV-Vis, NMR), and mutagenicity/genotoxicity studies were performed using biological assays (Ames assay, alkaline comet assay, MTT proliferation assay). In addition, computational approaches were used to confirm or expand empirical results. These included the study of reaction mechanisms by DFT, and the determination of equilibrium constants in solution using high-level ab initio methods. Also, the reach of the NBP assay as a tool for measuring alkylating capacity and its correlation with in vivo results have been reviewed. The results obtained help understand the lack of biological effects of diketene and oxetanes and the extreme ones observed for halohydroxifuranones. Also meaningful conclusions regarding the acidity and hydrolysis of esters were reached. CONTENTS 1 Alkylating agents and the NBP Test: a review. 2 Reactivity and alkylating potential of diketene. 3 Hydrolysis of lactones: Mechanisms and energy barriers. 4 Alkylating potential of oxetanes. 5 Reactivity and alkylating potential of hydroxyhalofuranones. A DNA-Intercalating photochromic spiropyran