Original scientific paper

NMR Conformational Study Reveals that S-C-N Anomeric Effect in Thionucleosides Is Weaker than O-C-N Anomeric Effect in Natural Nucleosides

Martin Črnugelj ; NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1115 Ljubljana, Slovenia
Janez Plavec orcid.org/0000-0003-1570-8602 ; NMR Center, National Institute of Chemistry, Hajdrihova 19, SI-1115 Ljubljana, Slovenia

Abstract

The comparative analysis by NMR and ab initio calculations of the energetics of North ⇄ South pseudorotational equilibrium in 4'-thio-nucleosides and in their natural 4'-oxo counterparts has shown that S-C-N anomeric effect in the former is weaker than O-C-N anomeric effect in the latter. The ΔΔH° values between 2'-deoxy-4'-thio analogues and their 4'-oxo counterparts after accounting for the drive by 3'-OH group have been attributed to the weakening of the nucleobase-dependent S4'-C1'-N9/1 anomeric effect by 3.3, 6.5, 8.5 and 9.2 kJ mol-1 in adenine, guanine, cytosine and thymine, respectively. In addition, S-C-N anomeric effect is stronger in purine than in pyrimidine 4'-thionucleosides and increases in the following order: thymine < cytosine < guanine < adenine, which is in contrast to natural nucleosides.

Keywords

NMR; nucleoside; conformational analysis; anomeric effect; pseudorotational equilibrium

Hrčak ID:

131829

URI

https://hrcak.srce.hr/131829

Publication date:

2.4.2001.

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