Reaction of epichlorohydrin with 2′-deoxynucleosides: characterization of adducts

Abstract

Epichlorohydrin (ECH) is a simple 3-carbon epoxide of industrial importance and thus has the potential for human exposure in the workplace. It has been shown to be genotoxic in several systems and is a compound capable of reacting with biological nucleophiles. This study details the products formed from the reaction of ECH with 2′-deoxynucleosides at pH 7 and 37 °C for 6 h. Reaction with 2′-deoxyguanosine yielded 7-(3-chloro-2-hydroxypropyl) guanine (7-CHP-Gua) resulting from alkylation at N-7 of 2′-deoxyguanosine followed by depurination. Two unusual adducts were also partially characterized which resulted from further reaction of 7-CHP-Gua with another molecule of ECH to yield 1,7-bis(3-chloro-2-hydroxypropyOguanine (1,7-bis-CHP-Gua) which could then cyclize with the exocyclic amino group to yield 1,N 2-(2-hydroxypropano)-7-(3-chloro-2-hydroxypropyl) guanine (1,N 2-HP-7-CHP-Gua). Reaction with 2′-deoxyadenosine gave only one product, namely 1,N 6-(2-hydroxypropano)-2′-deoxyadenosine (1,N 6-HP-dAdo). The reaction of 2′-deoxythymidine with ECH also yielded one product which was identified as 3-(3-chloro-2-hydroxypropyl)-2′-deoxythymidine (3-CHP-dThd). A 3-(3-chloro-2-hydroxypropyl)-2′-deoxyuridine (3-CHP-dUrd) product was isolated from the reaction of ECH with 2′-deoxycytidine. This product most likely resulted from the deamination of an initially formed 3-(3-chloro-2-hydroxypropyl)-2′-deoxycytidine (3-CHP-dCyd), a phenomenon which we have previously reported to occur during the reaction of 2′-deoxycytidine with other aliphatic epoxides. Evidence is also presented that 3-CHP-dUrd is converted to 3-(2,3-dihydroxypropyl)-2′-deoxyuridine (3-DHP-dUrd) under physiological conditions, with a half-life of 213 h. Reaction of ECH with calf thymus DNA (pH 7.0, 37 °C, 3 h) resulted in the formation of 7-CHP-Gua (200 nmol/mg DNA).