RNA Synthesis by Reverse Direction Process: Phosphoramidites and High Purity RNAs and Introduction of Ligands, Chromophores, and Modifications at 3′‐End

We have synthesized and studied the coupling properties of 3′‐DMT‐5′‐CE phosphoramidites. The coupling efficiency per step surpasses 99% in the reverse‐direction synthesis methodology, leading to high‐purity RNA in a large number of 20‐ to 21‐mers and long‐chain oligonucleotides. Our data show that 5′→︀3′ direction synthesis has a distinct advantage compared to the conventional method. As a result, this method of RNA synthesis is expected to be a very useful and practical method of choice for therapeutic‐grade RNA. The phosphoramidites, Rev‐A‐n‐bz, Rev‐C‐n‐bz, Rev‐C‐n‐ac, Rev‐G‐n‐ac, and Rev‐rU are routinely produced with an HPLC purity of greater than 98% and 31P NMR purity greater than 99.5%. Curr. Protoc. Nucleic Acid Chem. 45:3.20.1‐3.20.39. © 2011 by John Wiley & Sons, Inc.