Effect of temperature and protonation upon the conformation of 2'-o-methyladenosine. Correlation of conformational parameters in purine nucleosides.

Proton magnetic resonance studies of 2'-o-methyladenosine in 2H2O have been carried out at variable temperature and p2H. The chemical shifts and H-H coupling constants are discussed in terms of the molecular conformation. Comparison of the data with those of adenosine reveals that 2'-O-methylation has little influence on the conformation. At neutral p2H where the adenine base is not protonated, the molecules favor a 2' endo, gauche-gauche conformation. Protonation of the base at the N(1) position leads to a decrease in the 2' endo, gauche-gauche bias. The data for 2'-O-methyladenosine and adenosine, as well as for several other purine derivatives, reveal the presence of a correlation between the sugar pucker and the C(5')-C(4') conformer distribution which is the inverse of the correlation previously reported for pyrimidine derivatives.