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 2′‐thioadenosine ( Schemes 2 and 3 ), and its spontaneous and site‐specific aminoacylation with the weakly activated amino acid thioester HPheSPh ( 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.