Synthesis, Improved Antisense Activity and Structural Rationale for the Divergent RNA Affinities of 3;#8242;-Fluoro Hexitol Nucleic Acid (FHNA and Ara-FHNA) Modified Oligonucleotides

Journal Article · Fri Mar 16 04:00:00 EDT 2012 · J. Am. Chem. Soc.

DOI:https://doi.org/10.1021/ja207086x· OSTI ID:1032997

Egli, Martin; Pallan, Pradeep S; Allerson, Charles R; Prakash, Thazha P; Berdeja, Andres; Yu, Jinghua; Lee, Sam; Watt, Andrew; Gaus, Hans; Bhat, Balkrishen; Swayze, Eric E; Seth, Punit P ^[1]

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1. Isis Pharm.

The synthesis, biophysical, structural, and biological properties of both isomers of 3'-fluoro hexitol nucleic acid (FHNA and Ara-FHNA) modified oligonucleotides are reported. Synthesis of the FHNA and Ara-FHNA thymine phosphoramidites was efficiently accomplished starting from known sugar precursors. Optimal RNA affinities were observed with a 3'-fluorine atom and nucleobase in a trans-diaxial orientation. The Ara-FHNA analog with an equatorial fluorine was found to be destabilizing. However, the magnitude of destabilization was sequence-dependent. Thus, the loss of stability is sharply reduced when Ara-FHNA residues were inserted at pyrimidine-purine (Py-Pu) steps compared to placement within a stretch of pyrimidines (Py-Py). Crystal structures of A-type DNA duplexes modified with either monomer provide a rationalization for the opposing stability effects and point to a steric origin of the destabilization caused by the Ara-FHNA analog. The sequence dependent effect can be explained by the formation of an internucleotide C-F {hor_ellipsis} H-C pseudo hydrogen bond between F3' of Ara-FHNA and C8-H of the nucleobase from the 3'-adjacent adenosine that is absent at Py-Py steps. In animal experiments, FHNA-modified antisense oligonucleotides formulated in saline showed a potent downregulation of gene expression in liver tissue without producing hepatotoxicity. Our data establish FHNA as a useful modification for antisense therapeutics and also confirm the stabilizing influence of F(Py) {hor_ellipsis} H-C(Pu) pseudo hydrogen bonds in nucleic acid structures.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: NIH
• OSTI ID: 1032997
• Journal Information: J. Am. Chem. Soc., Journal Name: J. Am. Chem. Soc. Journal Issue: (41) ; 10, 2011 Vol. 133; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

08 HYDROGEN
ADENOSINE
ANIMALS
ATOMS
CRYSTAL STRUCTURE
DNA
FLUORINE
GENES
HYDROGEN
ISOMERS
LIVER
MONOMERS
NUCLEIC ACIDS
OLIGONUCLEOTIDES
ORIGIN
PYRIMIDINES
RESIDUES
RNA
SACCHAROSE
STABILITY
SYNTHESIS
THYMINE