Application of Sugar-Base Anhydro Bridge for Modification of Nucleosides in the 2’- and/or 3’-Positions - Revisited

The nucleosides modified in the 2’- and/or 3’-position have been known for years and include important, bioactive compounds such as zidovudine, cytarabine, didanosine, puromycin, and fludarabine. This group consists of analogs with altered configuration, 2’,3’-dideoxy and 2’,3’-dideoxy-didehydro nucleosides, as well as derivatives with additional substituents. These compounds are often targeted against viruses and tumors. The sugar-base anhydro nucleosides have been known since the middle of the 20th century. However, their application has not yet been fully explored and described. The number of 2’,3’-dimodified derivatives, obtainable through sugar-base anhydrocyclic synthons, could be vast, especially taking into consideration various combinations of S-alkyl, S-aryl, O-alkyl, O-aryl, halogen, triazole, amine and azide substituents in both pyrimidine and purine nucleosides. Furthermore, application of anhydrocyclic structures can be an efficient method of introducing isotope labeled groups. The aim of this article is to provide an overview of the known methods of functionalization of the 2’- and/or 3’-position of nucleosides, using anhydrocyclic structures, and also to present a future outlook for this subject.