Design of a Ribosyltriazole-Annulated Cyclooctyne for Oligonucleotide Labeling by Strain-Promoted Alkyne-Azide Cycloaddition

A ribosyltriazole ring‐fused cyclooctyne was prepared and converted into the corresponding phosphoramidite, which was applied in the automated synthesis of DNA and RNA oligomers. Ensuing strain‐promoted alkyne–azide cycloaddition of the obtained oligonucleotides to fluorescent azides yielded the corresponding fluorescent oligonucleotide conjugates. The synthesis of a triazole‐annulated ribose cyclooctyne phosphoramidite and its subsequent use in the automated solid‐phase synthesis of oligonucleotides is described. Strain‐induced azide to alkyne [2+3] Huisgen dipolar cycloaddition of the cyclooctyne‐containing oligonucleotides with azide‐containing fluorescent dyes yields labeled oligonucleotides, including an example of a DNA–RNA duplex; TBDMS = tert‐butyldimethylsilyl, DMTr = 4,4′‐dimethoxytrityl.