Spontaneous aminoacylation of a RNA sequence containing a 3′-terminal-2′-thioadenosine

We report the synthesis of a modified 8mer RNA sequence, (C-C-C-C-A-C-C-(2'-thio)A)-RNA 5'-(dihydrogen phosphate) (9) containing a 3'-terminal T-thioadenosine (Schemes 2 and 3), and its spontaneous and site-specific aminoacylation with the weakly activated amino acid thioester H-Phe-SPh (12). This reaction, designed in analogy to the 'native chemical ligation' of oligopeptides, occurs efficiently in buffered aqueous solutions and under a wide range of conditions (Table). At pH Values between 5.0 and 7.4, two products, the 3'-O-monoacylated and the 3'-O,2'-S-diacylated RNA sequences 10 and 11 are formed fast and quantitatively (Scheme 4). At pH 7.4 and 37, the 3'-O-monoacylated product 10 is formed as major product in situ by selective hydrolysis of the O,S-diacylated precursor 11. Additionally, the preparation and isolation of the relevant 3'-O'-monoacylated product 10 was optimized at pH 5. The here presented concept could be employed for a straightforward aminoacylation of analogously modified tRNAs.