Efficient conversion of N 6 -threonylcarbamoyladenosine (t 6 A) into a tRNA native hydantoin cyclic form (ct 6 A) performed at nucleoside and oligoribonucleotide levels.

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.