New Efficient Synthesis of tRNA Related Adenosines Bearing the Hydantoin Ring (ct 6 A, ms 2 ct 6 A) by Intramolecular Cyclization of N 6 -(N-Boc-α-aminoacyl)-adenosine Derivatives.

A novel and efficient way for the synthesis of N 6 -hydantoin-modified adenosines, which utilizes readily available N 6 -(N-Boc-α-aminoacyl)-adenosine derivatives, was developed. The procedure is based on the epimerization-free, Tf 2 O-mediated conversion of the Boc group into an isocyanate moiety, followed by intramolecular cyclization. Using this method two recently discovered hydantoin modified tRNA adenosines, that is, cyclic N 6 -threonylcarbamoyl-adenosine (ct 6 A) and 2-methylthio-N 6 -threonylcarbamoyladenosine (ms 2 ct 6 A) were prepared in good yields.