Synthesis and Evaluation of Artificial Nucleic Acid Bearing an Oxanorbornane Scaffold

• Published in: Molecules (Basel, Switzerland) Switzerland), 2020-04, Vol.25 (7), p.1732
• Main Authors: Komine, Hibiki, Mori, Shohei, Morihiro, Kunihiko, Ishida, Kenta, Okuda, Takumi, Kasahara, Yuuya, Aoyama, Hiroshi, Yamaguchi, Takao, Obika, Satoshi
• Format: Article
• Language: English
• Subjects: Alcohol; Aptamers; Chemistry Techniques, Synthetic; Chromatography; Circular Dichroism; conformational restriction; Cotton; Cyclopentene; Deoxyribonucleic acid; DNA; duplex-forming ability; entropy; Exonuclease; Experiments; modified nucleic acid; modified oligonucleotide; Molecular Structure; Nucleic Acid Conformation; Nucleic acids; Nucleic Acids - chemical synthesis; Nucleic Acids - chemistry; Oligonucleotides - chemical synthesis; Oligonucleotides - chemistry; oxanorbornane; Scaffolds; Single-stranded DNA; Stability; Thermal denaturation; Thermodynamics; Uracil
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules25071732

Natural oligonucleotides have many rotatable single bonds, and thus their structures are inherently flexible. Structural flexibility leads to an entropic loss when unwound oligonucleotides form a duplex with single-stranded DNA or RNA. An effective approach to reduce such entropic loss in the duplex-formation is the conformational restriction of the flexible phosphodiester linkage and/or sugar moiety. We here report the synthesis and biophysical properties of a novel artificial nucleic acid bearing an oxanorbornane scaffold (OxNorNA), where the adamant oxanorbornane was expected to rigidify the structures of both the linkage and sugar parts of nucleic acid. OxNorNA phosphoramidite with a uracil (U) nucleobase was successfully synthesized over 15 steps from a known sugar-derived cyclopentene. Thereafter, the given phosphoramidite was incorporated into the designed oligonucleotides. Thermal denaturation experiments revealed that oligonucleotides modified with the conformationally restricted OxNorNA-U properly form a duplex with the complementally DNA or RNA strands, although the values of OxNorNA-U-modified oligonucleotides were lower than those of the corresponding natural oligonucleotides. As we had designed, entropic loss during the duplex-formation was reduced by the OxNorNA modification. Moreover, the OxNorNA-U-modified oligonucleotide was confirmed to have extremely high stability against 3'-exonuclease activity, and its stability was even higher than those of the phosphorothioate-modified counterparts ( p and p). With the overall biophysical properties of OxNorNA-U, we expect that OxNorNA could be used for specialized applications, such as conformational fixation and/or bio-stability enhancement of therapeutic oligonucleotides (e.g., aptamers).