Chemical synthesis of the 5-taurinomethyl(-2-thio)uridine modified anticodon arm of the human mitochondrial tRNA(Leu(UUR)) and tRNA(Lys).

5-Taurinomethyluridine (tau m(5)U) and 5-taurinomethyl-2-thiouridine (tau m(5)s(2)U) are located at the wobble position of human mitochondrial (hmt)tRNAL(Leu(UUR)) and tRNA(Lys), respectively. Both hypermodified units restrict decoding of the third codon letter to A and G. Pathogenic mutations in the genes encoding hmt-tRNA(Leu(UUR)) and hmt-tRNA(LYs) are responsible for the loss of the discussed modifications and, as a consequence, for the occurrence of severe mitochondria! dysfunctions (MELAS, MERRF). Synthetic oligoribonucleotides bearing modified nucleosides are a versatile tool for studying mechanisms of genetic message translation and accompanying pathologies at nucleoside resolution. In this paper, we present site-specific chemical incorporation of tau m(5)U and tau m(5)s(2)U into 17-mers related to the sequence of the anticodon arms hmt-tRNA(Leu) (UUR) and hmt tRNA(Lys), respectively employing phosphoramidite chemistry on CPG support. Selected protecting groups for the sulfonic acid (4-(tert-butyldiphenylsilanyloxy)-2,2-dimethylbutyl) and the exoamine function (-C(O)CF3) are compatible with the blockage of the canonical monomeric units. The synthesis of tau m(5)s(2)U-modified RNA fragment was performed under conditions eliminating the formation of side products of 2-thiocarbonyl group oxidation and/or oxidative desulphurization. The structure of the final oligomers was confirmed by mass spectroscopy and enzymatic cleavage data.