SYNTHESIS AND BIOCHEMICAL-CHARACTERIZATION OF N-1-GUANOSINE, N-2-GUANOSINE, AND N-7-GUANOSINE ADDUCTS OF BUTADIENE MONOXIDE

1,3-Butadiene is a known rodent carcinogen, but the molecular mechanis ms of its carcinogenicity are poorly understood. Butadiene monoxide (B M), a known mutagenic metabolite of 1,3-butadiene, was previously show n to react with guanosine to yield two N-7-guanine adducts. In the pre sent study, eight guanosine adducts of BM were purified and characteri zed as diastereomeric pairs of N-7-(2-hydroxy-3-buten-1-yl)guanosine ( G-1 and G-3), N-7-(1-hydroxy-3-buten-2-yl)guanosine (G-2 and G-5), N-2 -(1-hydroxy-3-buten-2-yl)guanosine (G-4 and G-7), and N-1-(1-hydroxy-3 -buten-2-yl)guanosine (G-6 and G-8) on the basis of stability studies and analyses by UV, H-1 NMR, and fast atom bombardment mass spectromet ry. While the N-7-adducts exhibited half-lives of approximately 50 (G- 1 and G-3) and 90 h (G-2 and G-5) upon incubation for 192 h in 100 mM phosphate buffer (pH 7.4) at 37 degrees C, the N-1- and N-2-adducts re mained stable. When guanosine was reacted with excess BM in phosphate buffer (pH 7.4) at 37 degrees C, adduct formation exhibited pseudo-fir st-order kinetics, with the N-7-adducts being formed approximately 10- fold more favorably than the N-1- and N-2-adducts. When incubations we re carried out at lower BM concentrations, the N-7-adducts remained th e major detectable adducts, but the N-2-adducts were also detectable a t equimolar BM and guanosine concentrations, and the N-1-adducts were detectable at a 5-fold molar excess of BM. These results, which provid e clear evidence that guanosine can be alkylated at multiple sites fol lowing 1,3-butadiene exposure, may aid in the development of useful bi omarkers for exposure to 1,3-butadiene. The results may also contribut e to a better understanding of the molecular mechanisms of 1,3-butadie ne-induced carcinogenicity.