Replacement of thymidine residues with 5-ethynyl-dU residues results in duplex stabilization. The degree of stabilization is less than that observed with propynyl-dU residues.⁽¹⁾ Oligonucleotides with 5-ethynyl residues may also be used in transition metal-catalyzed coupling reactions. Two ethynyl-bearing oligonucleotides can be homo-coupled via a diyne linkage using copper catalysis. Further, the ethynyl groups may be used in copper-catalyzed couplings with arylacetylenes bearing anthraquinone, biotin, or fluorescein appendages.⁽²⁾ Palladium catalyzed cross-coupling of ethynyl-dU-bearing oligonucleotidies with 2-iodoanthraquinone provides anthraquinone-bearing nucleic acids useful in electrochemical applications of DNA.⁽³⁾

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