Molecular orbital studies on the structure of nucleoside analogs. I. Conformation of 8-azapurine nucleosides.
PCILO (perturbative configuration interaction using localized orbitals) computations have been carried out for the conformational properties of 8-azapurine nucleosides. The results indicate an anti conformation for Xcn and a gg conformation for phiC(4')-C(5') for C(2')-endo 8-aza analogs compared to the syn and gg conformation for the corresponding purine nucleosides. For C(3')-endo sugar puckering, both molecules prefer the syn conformation due to intramolecular hydrogen bonding between O(5')-H of the sugar and N(3) of the base, the preference being more profound in 8-aza analogs. The crystallographic conformation 8-azaadenosine has been attributed to crystal forces. The available NMR data on 8-azapurine nucleosides are in agreement with the PCILO predictions.
D000241:Adenosine / Q000031:analogs & derivatives; D001372:Aza Compounds; D001375:Azaguanine / Q000031:analogs & derivatives; D006860:Hydrogen Bonding; D007288:Inosine / Q000031:analogs & derivatives; D008968:Molecular Conformation; D011684:Purine Nucleosides
D001372:Aza Compounds; D011684:Purine Nucleosides; D007288:Inosine; D000241:Adenosine; D001375:Azaguanine