A simple procedure is described to prepare nucleoside 3′(2′),5′-bisphosphates from the corresponding nucleosides with the use of pyrophosphoryl chloride. This method is rapid, gives nearly quantitative yields and, most importantly, can be used for a variety of nucleosides with base and sugar modifications. Since 3′,5′-bisphosphates are donors in the T4 RNA ligase reaction, a single residue can be enzymatically attached to the 3′ end of oligoribonucleotides. By these procedures, five different ring-modified nucleosides and one sugar-modified nucleoside were incorporated onto the 3′ end of (Ap)3C. In two cases, an additional step of synthesis with RNA ligase resulted in the modified nucleotide being located in an internal position in the oligonucleotide. Thus, a general method for the synthesis of oligoribonucleotides containing modified nucleosides is outlined. Since many of the modified nucleosides are fluorescent, oligomers containing them should be useful in a variety of physical and biochemical studies.
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