Sensitivity of the conformation of deoxyguanosine to binding at the C-8 position by N-acetylated and unacetylated 2-aminofluorene.

The conformation of N-(deoxyguanosin-8-yl)-2-acetylaminofluorene and N-(deoxyguanosin-8-yl)-2-aminofluorene was investigated by 1H n.m.r. spectroscopy. There was rotation about the glycosyl bond and preference for either the anti or syn conformation depended on whether or not the 8-arylamino nitrogen was acetylated. The unacetylated adduct existed preferentially in the anti form and the acetylated adduct existed preferentially in the alternate syn form. There was also rotation about the backbone C4' -C5' bond. The unacetylated adduct was mainly in the gauche-gauche conformation about C4'-C5', while the acetylated adduct was mainly in the alternate gauche-trans/trans-gauche form. Using space filling models with the conformation of the unacetylated adduct conserved in the helix, a possible structure of modified DNA was proposed which had less perturbation of the helix than that of the acetylated adduct. This was consistent with single strand endonuclease hydrolysis data. The acetylated and unacetylated adducts may cause entirely different types of local conformational changes in DNA because of major differences in interactions between the base and the sugar moiety at the modified nucleoside level.