DNA GUANINE ADDUCTS FROM 3-METHYL-1,2,3-OXADIAZOLINIUM IONS

The reaction of 3-methyl-1,2,3-oxadiazolinium tosylate 10, a close mod el for a putative reactive intermediate in the carcinogenic activation of ethanol nitrosamines such as (2-hydroxyethyl)methylnitrosamine 1, with various guanine derivatives, including acycloguanosine 12, deoxyg uanosine, deoxyguanosine monophosphate, and cyclic guanosine monophosp hate, various DNA oligomers, and calf-thymus DNA has been examined to determine whether this compound methylates and hydroxyethylates guanin e residues as proposed. In all of the transformations, 7-(2-(methylnit rosamino)ethyl)guanine (14) is the major product, following acidic hyd rolysis, and exceeds the formation of 7-methylguanine by ratios rangin g from 4:1 to 48:1, depending upon the guanine bearing substrate. O-6- (2(Methylnitrosamino)ethyl)deoxyguanosine (20) was prepared from the M itsunobu coupling of 1 and a protected deoxyguanosine derivative. 20 i s not produced in the reaction of 10 and deoxyguanosine and decomposes to 1 and guanine upon mild acid treatment, suggesting possible neighb oring group participation in its facile hydrolytic cleavage. kn of the major products from the reaction of 10 and 12 have been characterized , including the direct alkylation product, 7-(2-(methylnitrosamino)eth yl)acycloguanosine (13), and N-2-(2-(methylnitrosamino)ethyl)guanine, which was independently synthesized. Elucidation of the reactions of D NA with 10 and other electrophiles was facilitated by the development of both partial and total enzymatic hydrolysis assays utilizing P-32-5 '-labeled DNA oligotetramers containing one of each base type and HPLC with radiometric detection. The partial hydrolysis assay gives inform ation as to the type of base being modified, and the total hydrolysis assay permits a determination of the number of adducts produced for a given base. The assays permit a comparison between reactions where the same type of base adduct could be expected. Comparisons of the reacti ons of ethylene oxide and 10 using this methodology showed that 10 doe s not hydroxyethylate guanine in DNA.