Synthesis of TMG-capped RNA–DNA chimeric oligonucleotides

This paper deals with the synthesis of m32,2,7G5′pppAmpUmpApd(CpTpTpApCpCpT), a 5′-TMG-capped RNA–DNA chimeric oligonucleotide, which is expected to be conveyed to the nucleus by snurportin 1, a nuclear-transport protein. This 5′-TMG-capped RNA–DNA chimeric molecule was synthesized by the enzymatic condensation of m32,2,7G5′pppAmpUmpA with A5′ppd(CpTpTpApCpCpT) in the presence of RNA ligase. An inherent serious side reaction was disclosed in the 5′-adenylation of d(CpTpTpApCpCpT) on the solid support, but the use of an active ester intermediate as the pA donor gave an improved result.