Isonucleosides. Synthesis and biological activity

Synthesis of isonucleosides, compounds with the heterocyclic base placed at nonanomeric position is discussed. Such derivatives are synthesized either by nucleophilic substitution of a leaving group by activated base or by co nstruction of heterocyclic system at the amino group present at the sugar r ing. Alternative pathways of synthesis contain addition of heterocyclic bas e to the alpha,beta-unsaturated carbonyl sugar derivatives or 1,3-dipolar c ycloaddition. Some examples of isonucleosides biological activity are descr ibed.