Incorporation of N 2-Deoxyguanosine Metabolic Adducts of 2-Aminonaphthalene and 2-Aminofluorene into Oligomeric DNA

In previous work we described an efficient procedure for the synthesis of the respective N 2 and N 6 adducts of 2‘-deoxyguanosine (dG) and 2‘-deoxyadenosine (dA) derived from a series of aminoaryl compounds. We now outline methods for the site-specific introduction into oligomeric DNA of the adducts dG-N 2-AN (6), dG-N 2-AAN (7), dG-N 2-AF (8), and dG-N 2-AAF (9) derived from 2-aminonaphthalene (2-AN) or 2-aminofluorene (2-AF). For the 2-AN adduct 7, containing an acetylamino group, the 5‘-O-4,4‘-dimethoxytrityl- (DMT-) 3‘-O-phosphoramidite (14) required for automated DNA synthesis was synthesized in high yield via the sequence 10 → 11 → 14. On the other hand, introduction of the desacetyl adduct 6 into oligomeric DNA was accomplished via the N-trifluoroacetyl-DMT-phosphoramidite derivative 18. This involved a similar sequence (10 → 15 → 18) except that the order of the reactions was changed to avoid a decomposition that occurred when the silyl-protected amino derivative 11 was treated with trifluoroacetic anhydride. In the 2-AF series the 5‘-O-DMT-3‘-O-phosphoramidites 27a and 27b, related to 8 and 9, were prepared by similar methods. Again, however, the order of the reactions was changed to avoid the extreme insolubility associated with the N 2-[3-(2-acetylaminofluoren-3-yl)]dG (dG-N 2-AAF, 9) adduct that we had noted previously. The incorporation into oligomeric DNA of the acetylamino compounds 7 and 9 proceeded smoothly and in high yield (95−100%). By contrast, the trifluoroacetyl analogues led in both the naphthyl and fluorenyl series to a mixture of oligomers containing the desired free amino adduct (6 or 8) accompanied by the N-acetyl adduct (7 or 9, respectively, after the deprotection step), indicating secondary acetylation by the capping agent acetic anhydride.