Chemical synthesis of a very long RNA oligomer, a 110mer precursor-miRNA candidate, with 2-cyanoethoxymethyl (CEM) as the 2'-O-protecting group.

A long RNA oligomer, a 110mer with the sequence of a precursor-miRNA candidate, has been chemically synthesized in a single synthesizer run by means of standard automated phosphoramidite chemistry. The synthetic method involved the use of 2-cyanoethoxymethyl (CEM), a 2'-hydroxyl protecting group recently developed in our laboratory. We confirmed the identity of the synthetic 110mer by MALDI-TOF mass spectrometry, as well as HPLC, electrophoretic methods, RNase-digestion experiments, and its in vitro gene-silencing activity. The chemical synthesis of RNA oligomers of more than 100 nucleotides, which has until now been extremely difficult, can be practically realized by the CEM method.