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 (1)H 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 (13)C NMR spectra have also been examined, but no effect which could be ascribed to the stacking phenomena was observed in the carbon chemical shifts.