Chemical synthesis of a pentaribonucleoside tetraphosphate constituting the 3'-acceptor stem sequence of E. coli tRNAIle using 2'-O-(3-methoxy-1,5-dicarbomethoxypentan-3-yl)-ribonucleoside building blocks. Application of a new achiral and acid-labile 2'-hydroxyl protecting group in tRNA synthesis.

A synthesis of a pentaribonucleotide fragment constituting the residues 59-63 of 3'-terminus of E. coli tRNAIle, 5'-ApGpUpCpC-3', has been carried out using a new, easily accessible and achiral 2'-ketal protecting group. The new 2'-ketal group has an additional advantage in that it is easily functionalized to the diamide with aqueous ammonia in the penultimate step of deblocking of fully protected oligoribonucleotides. Such a functionalization of the 2'-ketal group at the penultimate step of deblocking of the fully protected tRNA molecule enhances its relative rate of removal under an acidic condition with a minimum of damage of the target tRNA molecule.