Ribose conformations in the common purine(beta)ribosides, in some antibiotic nucleosides, and in some isopropylidene derivatives: a comparison.

With the use of PMR the ribose conformations have been studies in the temperature range -60 to +40 degrees C in ND3 solutions of adenosine (A), guanosine (G), inosine (I), xanthsine (X), purineriboside (PR), 2-aminopurineriboside (2amPR), N6-isopentenyladenosine (N6ipA), 8-bromoadenosine (iA), and isopropylideneguanosine (iG). The aanlysis is based on the two-state S in equilibrium N model of the ribose moiety proposed by Altona and Sundaralingam. The compounds studied can be classified into two groups: 1. A, I, G, X, PR, 2amPR, N6ipA, and T show a small temperature dependence of thnd F have a stronger temperature dependence and [S] approximately 0.8. Within these two groups the similarities observed are greater than observed in the solid state. Some thermodynamic conclusions about the S in equilibrium N and the syn in equilibrium anti equilibria are presented. The results support the previously proposed correlation of the S state of the ribose with the syn conformation of the base and of the N state of the ribose with the anti conformation of the base. Furthermore, it is derived that the gg rotamer is correlated with the S state of the ribose and therefore stabilizes the syn conformation of the base.