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.

RNA Synthesis: phosphoramidites for RNA synthesis in the reverse direction. Highly efficient synthesis and application to convenient introduction of ligands, chromophores and modifications of synthetic RNA at the 3'-end.

Defined sequence RNA synthesis by 3'-->5' direction is now well established and currently in use for synthesis and development of vast variety of therapeutic grade RNA and Si RNA etc. A number of such synthetic RNA requires a modification or labeling of 3'- end of an oligonucleotide. The synthesis of 3'- end modified RNA requiring lipophilic, long chain ligands or chromophores, using 3' --> 5' synthesis methodology is challenging, requires corresponding solid support and generally results in low coupling efficiency and lower purity of the final oligonucleotide in general because of large amount of truncated sequences containing desired hydrophobic modification.