1985 Volume 58 Issue 6 Pages 1674-1677
Conformational properties of various title compounds in aqueous solution were examined with the aid of 500 MHz 1H-NMR spectroscopy. In particular, the signals of aromatic protons on both the indazole and adenine rings were shifted to higher fields without exception, compared with the corresponding signals in indazole and adenine mononucleotides. These observations, which can be explained as resulting from diamagnetic shielding effect of the indazole and adenine rings, indicate that the base pairs in the dinucleotides are closely stacked in parallel planes. On the other hand, the average conformation of riboses were deduced from J1′,2′-values as a proportion of N\ ightleftarrowsS equilibrium composition. Indazole riboses showed a roughly 50/50 equilibrium, whereas adenine riboses showed a small preference for the N-type conformer. Such a conformational state may be indispensable for taking up the strongly folded conformation between the base pairs in the dinucleotides, as judged by a somewhat favored S-type conformation of both riboses in the indazole- and adenine mononucleotides.
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