Proton NMR study on two structures of 3′-O-(acetylimino)3′-de(phosphinico)-thymidylyl-(3,5′)-deoxythymidine in aqueous solution

The solution structure of one of dithymidine monophosphate (TpT) analogues, containing an (N-acetyl)imino backbone linkage (NCOCH3) of 3′-O-(acetylimino)3′-de(phosphinico)-thymidylyl-(3,5′)-deoxythymidine (TNT), has been determined by proton NMR. Two structures, designated as major and minor forms, in a ratio of about 3:2 coexist when the solution temperature is <25°C. Both forms adopt anti conformation with respect to the glycosidic bond, S-type deoxyribofuranose pucker, and have no base stacking. The backbone torsion angles ε′, φON, φNC, and γ′ are trans, gauche+, gauche+, and gauche+ for the major form; and gauche−, gauche−, gauche−, and gauche+ for the minor form. Only major form is found at >25°C.