Conformations of the Nucleoside Analogs Formycin, 2-Azaadenosine, and Nebularine in Solution

Lüdemann, H.-D.; Westhof, E.

Conformations of the Nucleoside Analogs Formycin, 2-Azaadenosine, and Nebularine in Solution

2014

Lüdemann, H.-D. | Westhof, E.

The ribose conformations of formycin, 2-azaadenosine, nebularine, 8-bromoinosine, and 8-bromo- xanthosine have been studied using proton magnetic resonance in ND₃ solutions, in D₂O solutions, and in pyridine solutions. The temperature was varied between - 60 °C and +40 °C in ND₃ and between +10 °C and +60 °C in D₂O solutions. In solution, 2-azaadenosine and nebularine have a conformational behaviour similar to that of the common purine (β) ribosides. This is in agreement with the conformations observed in the solid state. The conformations of formycin and formycin B have strong analogies with those of the 8-bromopurineribosides and differ significantly from those of the 8-azapurineribosides since they adopt preferentially the syn-S-g⁺ conformation. This conformation is very probably stabilized by an intramolecular hydrogen bond between O (5′) and N (3).

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