Triazole- and Tetrazole-Bridged Nucleic Acids: Synthesis, Duplex Stability, Nuclease Resistance, and in Vitro and in Vivo Antisense Potency

Abstract

Antisense oligonucleotides are attractive therapeutic agents for several types of disease. One of the most promising modifications of antisense oligonucleotides is the introduction of bridged nucleic acids. As we report here, we designed novel bridged nucleic acids, triazole-bridged nucleic acid (TrNA), and tetrazole-bridged nucleic acid (TeNA), whose sugar conformations are restricted to N-type by heteroaromatic ring-bridged structures. We then successfully synthesized TrNA and TeNA and introduced these monomers into oligonucleotides. In UV-melting experiments, TrNA-modified oligonucleotides exhibited increased binding affinity toward complementary RNA and decreased binding affinity toward complementary DNA, although TeNA-modified oligonucleotides were decomposed under the annealing conditions. Enzymatic degradation experiments demonstrated that introduction of TrNA at the 3'-terminus rendered oligonucleotides resistant to nuclease digestion. Furthermore, we tested the silencing potencies of TrNA-modified antisense oligonucleotides using in vitro and in vivo assays. These experiments revealed that TrNA-modified antisense oligonucleotides induced potent downregulation of gene expression in liver. In addition, TrNA-modified antisense oligonucleotides showed a tendency for increased liver biodistribution. Taken together, our findings indicate that TrNA is a good candidate for practical application in antisense methodology.

Tellurium-Modified Nucleosides, Nucleotides, and Nucleic Acids with Potential Applications

“…Notably, modified nucleic acid has played a vital role in almost all the above applications, because of the narrow chemical diversity and poor physiological stability of nucleic acids which restrict their utilization. Various strategies of modification have been employed to develop novel DNA and RNA analogs to overcome those limitations, such as changing the structure of the backbones [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ], sugars [ 49 , 50 , 51 , 52 , 53 , 54 , 55 ], nucleobases [ 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ], introducing different functional groups to endow the nucleic acid with specific function [ 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ], or introducing special elements that do not exist in nucleic acids such as fluorine [ 74 , 75 , 76 , 77 ], bromine [ 78 , 79 , 80 ], mercury [ 81 ], and other heavy atoms [ 82 ].…”

Synthesis of Phosphorodiamidate Oligonucleotide Dimers

“…Today the demand for Oligos has escalated beyond the lab, as Oligos have become useful tools for not only modern medicine but also for molecular and synthetic biology, diagnostics, and more recently for data storage . The Oligo chemist’s toolbox of building blocks now includes exotic monomers such as bridged or locked nucleic acids (LNA), constrained ethyl and methoxyethyl monomers (cEt and cMOE), phosphorothioate, modified bases, modified and pseudo sugars, amino nucleosides, and more …”