© 2008 Oxford University Press
This article appears in the following Nucleic Acid Symposium Series issue: Joint Symposium of the 18th International Roundtable on Nucleosides, Nucleotides and Nucleic Acids and the 35th International Symposium on Nucleic Acids Chemistry [View the issue table of contents]
Design, Synthesis And Evaluation Of Constrained Methoxyethyl (cMOE) and Constrained Ethyl (cEt) Nucleoside Analogs
1Medicinal Chemistry, 2Drug Discovery, and 3Structural Biology, Isis Pharmaceuticals, Inc. 1891 Rutherford Road, Carlsbad, CA 92008. USA
*Corresponding Author. E-mail: pseth{at}isisph.com
Abstract
Antisense drug discovery technology is a powerful method to modulate gene expression in animals and represents a novel therapeutic platform.1 We have previously demonstrated that replacing 2'Omethoxyethyl (MOE, 2) residues in second generation antisense oligonucleotides (ASOs) with LNA (3) nucleosides improves the potency of some ASOs in animals. However, this was accompanied with a significant increase in the risk for hepatotoxicity.2 We hypothesized that replacing LNA with novel nucleoside monomers that combine the structural elements of MOE and LNA might mitigate the toxicity of LNA while maintaining potency. To this end we designed and prepared novel nucleoside analogs 4 (S-constrained MOE, S-cMOE) and 5 (R-constrained MOE, R-cMOE) where the ethyl chain of the 2'O-MOE moiety is constrained back to the 4' position of the furanose ring. As part of the SAR series, we also prepared nucleoside analogs 7 (S-constrained ethyl, S-cEt) and 8 (Rconstrained Ethyl, R-cEt) where the methoxymethyl group in the cMOE nucleosides was replaced with a methyl substituent. A highly efficient synthesis of the nucleoside phosphoramidites with minimal chromatography purifications was developed starting from cheap commercially available starting materials. Biophysical evaluation revealed that the cMOE and cEt modifications hybridize complementary nucleic acids with the same affinity as LNA while greatly increasing nuclease stability. Biological evaluation of oligonucleotides containing the cMOE and cEt modification in animals indicated that all of them possessed superior potency as compared to second generation MOE ASOs and a greatly improved toxicity profile as compared to LNA.