A t 6 A nucleoside was efficiently and stereospecifically transformed into a hydantoin cyclic form of N 6 -l-threonylcarbamoyladenosine (ct 6 A) by the use of polymer bounded carbodiimide (EDC-P) and HOBt. The procedure was successfully applied for a post-synthetic conversion of t 6 A-containing RNA 17-mers (of the sequences of anticodon stem and loop (ASL) fragments of S. pombe tRNA i  and E. coli tRNA Lys ) into the products bearing the ct 6 A unit.