DNA Containing Side Chains with Terminal Triple Bonds: Base‐Pair Stability and Functionalization of Alkynylated Pyrimidines and 7‐Deazapurines

Abstract
The synthesis of a series of oligonucleotides containing 5‐substituted pyrimidines as well as 7‐substituted 7‐deazapurines bearing diyne groups with terminal triple bonds is reported. The modified nucleosides were prepared from the corresponding iodo nucleosides and diynes by the Sonogashira cross‐coupling reaction. They were converted into phosphoramidites and employed in solid‐phase synthesis of oligonucleotides. The effect of the diyne modifications on the duplex stability was investigated. The modified nucleosides were used for further functionalization using the protocol of Huisgen–Sharpless [2+3] cycloaddition (‘click chemistry’).