Determination of the syn-anti Equilibrium of Some Purine 3':5'-Nucleotides by Nuclear-Magnetic-Relaxation Perturbation in the Presence of a Lanthanide-Ion Probe

Abstract
The aqueous solution conformation of four purine 3′:5′-nucleotides varying in their substituents at C-6 and C-8 has been studied using gadolinium(III) to perturb the proton relaxation times. The ribose conformations are inferred. All the nucleotides are best described as being in a dynamic equilibrium between syn and anti conformations and the position of this equilibrium is not dramatically affected by changing the substituent at C-6. These nucleotides in their neutral base form slightly favour an anti conformation. In the presence of a bulky methylthio group at C-8 the equilibrium is shifted towards a dominance from the syn conformation due to steric repulsion factors.

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