CHEMICAL MODIFICATION OF DEOXYCYTIDINE AT DIFFERENT SITES YIELDS ADDUCTS OF DIFFERENT STABILITIES - CHARACTERIZATION OF N-3-DEOXYCYTIDINE AND O-2-DEOXYCYTIDINE AND N-3-DEOXYURIDINE ADDUCTS OF BUTADIENE MONOXIDE

Eight adducts were characterized from the reaction of deoxycytidine wi th the chemical carcinogen, butadiene monoxide (BM). They were identif ied as diastereomeric pairs of N-3-(2-hydroxy-3-buten-l-yl)deoxycytidi ne, N-3-(2-hydroxy-3-buten-l-yl)deoxyuridine, N-3-(l-hydroxy-3-buten-2 -yl)deoxyuridine, and O-2-(2-hydroxy-3-buten-l-yl)deoxycytidine based on UV spectra, H-1 NMR, FAB/MS, and stability studies. The N-3-(2-hydr oxy-3-buten-1-yl)deoxycytidine adducts were unstable at pH 7.4, 37 deg rees C, and deaminated to the corresponding N-3-deoxyuridine adducts w ith half-lives of 2.3 and 2.5 h. The N-3-(l-hydroxy-3-buten-2-yl)deoxy cytidine diastereomers were not detected, apparently because of faster rates of deamination compared to the N-3-(2-hydroxy-3-buten-l-yl)deox ycytidine adducts. The corresponding four N-3-deoxyuridine adducts wer e stable for up to 168 h. The O-2-deoxycytidine adducts were unstable and decomposed with a half-life of 11 h. The N-3-(2-hydroxy-3-buten-l- yl) deoxycytidine adducts were initially the major adducts formed upon reaction of deoxycytidine with BM at 37 degrees C in phosphate buffer (pH 7.4), but the corresponding N-3-deoxyuridine adducts showed a lag in formation due to the time needed for deamination. The N-3-(l-hydro xy-3-buten-2-yl)deoxyuridine and O-2-deoxycytidine adducts had linear formation rates, but were formed to a lesser extent. Heating the react ion mixture at 80 degrees C for 1 h converted all N-3-deoxycytidine ad ducts to the stable N-3- deoxyuridine adducts. Incubation of deoxycyti dine with an excess of BM at pH 7.4, 37 degrees C, followed by the ext raction and heating steps allowed calculation of the pseudo-first-orde r kinetic rate constants for the four uridine adducts. If the heating step was eliminated, then the pseudo-first-order kinetic rate constant s could be calculated for the N-3-(2-hydroxy-3-buten-l-yl) deoxycytidi ne and O-2-(2-hydroxy 3-buten-l-yl)deoxycytidine adducts. The rate con stants for N-3-(2-hydroxy-3-buten1-yl)deoxycytidine and the correspond ing N-3-(2-hydroxy-3-buten1-yl)deoxyuridine were five- to sixfold the rate constants for the N-3-(l-hydroxy-3-buten-2-yl) deoxyuridine and O -2-(2-hydroxy-3-buten-l-yl)deoxycytidine adducts. Thus, the results sh ow that the reaction of deoxycytidine with BM yields adducts at differ ent sites with different rates of formation and stabilities. Understan ding the chemical interactions of deoxycytidine with BM and the stabil ity of the various adducts may contribute to a better understanding of the molecular mechanisms of mutagenesis and carcinogenesis of BM and the development of useful biomarkers of exposure. (C) 1997 Academic Pr ess