A conformational study of some adenosines by use of nuclear Overhauser effect

Conformations of 8-bromo-2′-[unk]-triisopropylbenzenesulfonyladenosine ([unk]) and its 3′-[unk]-isomer ([unk]) in solution have been determined by the use of intramolecular nuclear Overhauser effects in ¹H NMR spectroscopy. Compound [unk] has been proved to have a conformation in which the adenosine and benzene rings are intramolecularly stacked and compound [unk] an elongated non-stacked conformation in dimethylsulphoxide. The 5′-[unk]-acetyl derivative of [unk] has also been found to adopt the intramolecularly stacked conformation in dimethylsulphoxide, but a non-stacked one in chloroform. Coupling constants observed are discussed in connection with the conformation of the ribose moiety. The ¹³C NMR spectra have also been examined, but no effect which could be ascribed to the stacking phenomena was observed in the carbon chemical shifts.