| Abstract
| - A straightforward approach to a novel class of ribo-type cyclohexenyl nucleosides is described. Anelectron-demand Diels−Alder reaction forms the key-step of the chosen synthetic pathway. Althoughthe difference is small, conformational analysis using NMR shows that this nucleoside analogueadopts preferentially an 2H3 conformation (S-type), while the “deoxy” cyclohexenyl analogue has apreference for a C3‘ endo conformation (N-type). Analyses of the conformational equilibrium revealthat, in the given experimental conditions, the difference between adenosine and its cyclohexenylcongener resides in their different ΔG values; furthermore, in adenosine, the conformationalpreference is of enthalpic origin, whereas in the cyclohexenyl congener, the conformational preferenceis of entropic origin.
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