Synthesis of tRNA analogues containing a terminal ribose locked in the South conformation to study tRNA-dependent enzymes.

We report here the synthetic route of two constrained dinucleotides and the determination of the sugar puckering by NMR analyses of the starting nucleosides. Enzymatic ligation to microhelix-RNAs provide access to tRNA analogues containing a 3' terminal A ⁷⁶ locked in South conformation. Biological evaluation of our tRNA analogues has been performed using amino-acyl tRNA-dependent transferase FemX _Wv , which mediates non-ribosomal incorporation of amino acids into the bacterial cell wall. We have shown that our tRNA analogues inhibited the aminoacyl transfer reaction catalyzed by FemX _Wv with IC _50s of 10 and 8 μM. These results indicate that FemX _Wv displays a moderate preference for tRNAs containing a terminal A ⁷⁶ locked in the South conformation and that a South to North switch in the conformation of the terminal ribose might contribute to the release of the uncharged tRNA ^Ala product of the aminoacyl transfer reaction catalyzed by FemX _wv .