Ribose Conformations of Adenosine Analogs Modified at the 2', 3' or 5' Positions
2014
Klimke, G. | Cuno, I. | Lüdemann, H.-D. | Mengel, R. | Robins, Ned
The solution conformation of adenosine(β)ribosides modified at the 2′, 3′ or 5′ position is derived from the analysis of the HRNMR spectra of the ribose protons. The conformational equilibria of the furanoside rings are described by the two state N ↔ S model introduced by Altona and Sundaralingam. The new compounds studied are: 2′-thiobenzoyl-2′-deoxyadenosine, 3′-thio-3′-deoxyadenosine, 2′-chloro-2′-deoxyadenosine, 3′-chloro-3′-deoxyadenosine, 2′-bromo- 2′-deoxyadenosine, 3′-bromo-3′-deoxyadenosine, 2′-O-methyladenosine, 3′-O-methyl-adenosine, 2,-deoxy-3,-O-methyladenosine, 5′-amino-5′-deoxyadenosine, 5′-acido-5′-deoxyadenosine, and 5′-chloro-5′-deoxyadenosine. The emphasis in this work is to study systematically the influence of the different substituents upon the conformational equilibria of the sugar. It is found that any substitution at the 2′ position stabilizes the S-conformer. An even more pronounced stabilization of the A-conformer in the 3′ substituted analogs is observed. The equilibrium changes in these classes of compounds can neither be correlated quantitatively with electronegativity differences nor with sterical differences between the various substituents. Substitution at the 5′ position influences the N ↔ S equilibrium only slightly, but has significant effects upon the conformational preferences of the exocyclic 5′-CH₂R₃ group.
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