Synthesis and conformational analysis of a ribo-type cyclohexenyl nucleoside
Sara Vijgen1, Koen Nauwelaerts, Jing Wang
1Laboratory of Medicinal Chemistry, Rega Institute for Medical Research, Katholieke Universiteit Leuven, Minderbroedersstraat 10, B-3000, Leuven, Belgium.
Abstract:
A straightforward approach to a novel class of ribo-type cyclohexenyl nucleosides is described. An electron-demand Diels-Alder reaction forms the key-step of the chosen synthetic pathway. Although the difference is small, conformational analysis using NMR shows that this nucleoside analogue adopts preferentially an 2H3 conformation (S-type), while the "deoxy" cyclohexenyl analogue has a preference for a C3' endo conformation (N-type). Analyses of the conformational equilibrium reveal that, in the given experimental conditions, the difference between adenosine and its cyclohexenyl congener resides in their different DeltaG values; furthermore, in adenosine, the conformational preference is of enthalpic origin, whereas in the cyclohexenyl congener, the conformational preference is of entropic origin.
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