Synthesis of a benzene metabolite adduct, 3''-hydroxy-1,N-2-benzetheno-2'-deoxyguanosine, and its site-specific incorporation into DNA oligonucleotides

p-Benzoquinone (p-BQ) is a stable metabolite of benzene and a number of other drugs and chemicals. 2'-Deoxyguanosine was allowed to react with p-BQ in aqueous solution (pH 4.5, 7.4, and 9.3). At pH 7.4 and 9.3 one major product was found in low yield; at pH 4.5 no product was detected. In nonaqueous conditions (DMF or DMSO, in the presence of K2CO3), an unstable intermediate with two p-BQ moieties was found which slowly converted to the product formed in aqueous solution. These products were isolated by silica gel, column chromatography, or reverse-phase HPLC and characterized by UV, H-1 NMR, FAB-MS, and electrospray MS. The major stable product of the reaction of dG with p-BQ is an exocyclic compound, 3''-hydroxy-1,N-2-benzetheno-2'-deoxyguanosine (p-BQ-dG). Incorporation of the adduct into oligonucleotides requires the protection of three hydroxyl groups (C7, 5', 3') and the amino group at N5. The exocyclic hydroxyl and the amino group were protected by acylation after protecting the 5- and the S'-hydroxyl groups of the sugar moiety by 4,4'-dimethoxytrityl and a cyanoethyl N,N-diisopropylphosphoramidite group, respectively. This is the first time the fully protected phosphoramidite of p-BQ-dG has been prepared and used in the synthesis of site specifically modified oligonucleotides. After deprotection with 1,3-diazabicyclo[5.4.0]undec-7-ene (DBU), in ethanol, oligomers purified by gel electrophoresis and HPLC. Enzymatic hydrolysis and analysis by HPLC confirmed the presence of p-BQ-dG in the oligomers. These oligomers are now under investigation for their biochemical properties.