A t⁶A nucleoside was efficiently and stereospecifically transformed into a hydantoin cyclic form of N⁶-L-threonylcarbamoyladenosine (ct⁶A) by the use of polymer bounded carbodiimide (EDC-P) and HOBt. The procedure was successfully applied for a post-synthetic conversion of t⁶A-containing RNA 17-mers (of the sequences of anticodon stem and loop (ASL) fragments of S. pombe tRNAⁱ and E. coli tRNA^Lys) into the products bearing the ct⁶A unit.