Base displacement in AAF and AF modified dCpdG: syn and anti Guanine

Minimized conformational potential energy calculations have been performed for the major adduct of N‐2‐acetylaminofluorene (AAF) and aminofluorene (AF) with dCpdG. The DNA backbone conformations that produce base displacement, about which no information was previously available, were ascertained. For the AAF adduct, five different combinations of the DNA backbone torsions ω', ω and ψ produce low‐energy conformers in which the fluorene is coplanar with cytidine, and the guanine is syn and twisted nearly perpendicular to the AAF. For the deacetylated AF adduct, three additional backbone types yielded fluorene‐cytidine stacked conformers. In these conformers the guanine was anti. The various modes of achieving base‐displacement may occur under differing circumstances, such as extent of modification, base sequence, salt concentration, and the nature of the adduct (acetylated or deacetylated).