Synthesis of Oligonucleotides Carrying 5′‐5′ Linkages Using Copper‐Catalyzed Cycloaddition Reactions

There is considerable interest in coupling oligonucleotides to molecules and surfaces. Although amino- and thiol-containing oligonucleotides are being successfully used for this purpose, cycloaddition reactions may offer greater advantages due to their higher chemoselectivity and speed. In this study, copper-catalyzed 1,3-dipolar cycloaddition reactions between oligonucleotides carrying azido and alkyne groups are examined. For this purpose, several protocols for the preparation of oligonucleotides carrying these two groups are described. The non-templated chemical ligation of two oligonucleotides via copper-catalyzed [3+2] cycloaddition is described. By solid-phase methodology, oligonucleotides carrying 5'-5' linkages can be obtained in good yields.