Chemical route to the capped RNAs.
Eukaryotic and viral messenger RNAs contain a CAP structure that plays an important role in the initiation of translation and several other cellular processes that involve mRNAs. In this paper, we report a convenient chemical approach to the preparation of milligram quantities of short, capped RNA oligonucleotides, which overcomes some of the limitations of previous approaches. The method is based on the use of a reactive precursor, m7GppQ [P1-7-methylguanosine-5'-O-yl, P2-O-8-(5-chloroquinolyl) pyrophosphate]. The precursor reacts smoothly with 5'-phosphorylated unprotected short RNA in the presence of CuCl2 in organic media. The feasibility of this approach was demonstrated by the synthesis of the capped pentaribonucleotide m7GpppGpApCpU. The synthesized capped oligonucleotide was isolated and purified by reverse phase and ion exchange HPLC with a final yield of 37%. The structure of the m7GpppGpApCpU was confirmed by 31P NMR, mass-spectrometry and enzymatic hydrolysis.