4'-C-Methoxy-2'-deoxy-2'-fluoro Modified Ribonucleotides Improve Metabolic Stability and Elicit Efficient RNAi-Mediated Gene Silencing.
Malek-Adamian, E., Guenther, D.C., Matsuda, S., Martinez-Montero, S., Zlatev, I., Harp, J., Burai Patrascu, M., Foster, D.J., Fakhoury, J., Perkins, L., Moitessier, N., Manoharan, R.M., Taneja, N., Bisbe, A., Charisse, K., Maier, M., Rajeev, K.G., Egli, M., Manoharan, M., Damha, M.J.(2017) J Am Chem Soc 139: 14542-14555
- PubMed: 28937776 
- DOI: https://doi.org/10.1021/jacs.7b07582
- Primary Citation of Related Structures:  
5VR4 - PubMed Abstract: 
We designed novel 4'-modified 2'-deoxy-2'-fluorouridine (2'-F U) analogues with the aim to improve nuclease resistance and potency of therapeutic siRNAs by introducing 4'-C-methoxy (4'-OMe) as the alpha (C4'α) or beta (C4'β) epimers. The C4'α epimer was synthesized by a stereoselective route in six steps; however, both α and β epimers could be obtained by a nonstereoselective approach starting from 2'-F U. 1 H NMR analysis and computational investigation of the α-epimer revealed that the 4'-OMe imparts a conformational bias toward the North-East sugar pucker, due to intramolecular hydrogen bonding and hyperconjugation effects. The α-epimer generally conceded similar thermal stability as unmodified nucleotides, whereas the β-epimer led to significant destabilization. Both 4'-OMe epimers conferred increased nuclease resistance, which can be explained by the close proximity between 4'-OMe substituent and the vicinal 5'- and 3'-phosphate group, as seen in the X-ray crystal structure of modified RNA. siRNAs containing several C4'α-epimer monomers in the sense or antisense strands triggered RNAi-mediated gene silencing with efficiencies comparable to that of 2'-F U.
Organizational Affiliation: 
Department of Chemistry, McGill University , 801 Sherbrooke Street West, Montreal, Quebec H3A 0B8, Canada.