Copper catalyzed cycloaddition for the synthesis of non isomerisable 2′ and 3′-regioisomers of arg-tRNAarg

In this report, non-isomerisable analogs of arginine tRNA (Arg-triazole-tRNA) have been synthesized as tools to study tRNA-dependent aminoacyl-transferases. The synthesis involves the incorporation of 1,4 substituted-1,2,3 triazole ring to mimic the ester bond that connects the amino acid to the terminal adenosine in the natural substrate. The synthetic procedure includes (i) a coupling between 2′- or 3′-azido-adenosine derivatives and a cytidine phosphoramidite to access dinucleotide molecules, (ii) Cu-catalyzed cycloaddition reactions between 2′- or 3′-azido dinucleotide in the presence of an alkyne molecule mimicking the arginine, providing the corresponding Arg-triazole-dinucleotides, (iii) enzymatic phosphorylation of the 5′-end extremity of the Arg-triazole-dinucleotides with a polynucleotide kinase, and (iv) enzymatic ligation of the 5′-phosphorylated dinucleotides with a 23-nt RNA micro helix that mimics the acceptor arm of arg-tRNA or with a full tRNA^arg. Characterization of nucleoside and nucleotide compounds involved MS spectrometry, ¹H, ¹³C and ³¹P NMR analysis. This strategy allows to obtain the pair of the two stable regioisomers of arg-tRNA analogs (2′ and 3′) which are instrumental to explore the regiospecificity of arginyl transferases enzyme. In our study, a first binding assay of the arg-tRNA micro helix with the Arginyl-tRNA-protein transferase 1 (ATE1) was performed by gel shift assays.