Rn. Loeppky et al., DNA GUANINE ADDUCTS FROM 3-METHYL-1,2,3-OXADIAZOLINIUM IONS, Journal of the American Chemical Society, 118(45), 1996, pp. 10995-11005
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.