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Cyclic nucleosides and stereochemistry

المؤلف:  Jonathan Clayden , Nick Greeves , Stuart Warren

المصدر:  ORGANIC CHEMISTRY

الجزء والصفحة:  ص1138-1139

2025-08-12

557

Cyclic nucleosides and stereochemistry

 DNA is more stable than RNA because its sugars lack the 2′ hydroxyl groups. In ribonucleic acids, the fact that the 2′- and 3′-OH groups are on the same side of the ring makes alkaline hydrolysis exceptionally rapid by intramolecular nucleophilic catalysis.

The base removes a proton from the 2′-OH group, which cyclizes on to the phosphate link— possible only if the ring fusion is cis. The next reaction involves breakdown of the penta covalent phosphorus intermediate to give a cyclic phosphate. One nucleoside is released by this reaction and the second follows when the cyclic phosphate is itself cleaved by base. Another cyclic phosphate that can be formed from a nucleotide is important as a biological messenger that helps to control such processes as blood clotting and acid secretion in the stomach. It is cyclic AMP (cAMP), formed enzymatically from ATP by nucleophilic displace ment of pyrophosphate by the 3′-OH group.