Application of unnatural oligonucleotides to chemical modification of gene expression

Chemical entities that specifically interact with biological molecules can reveal the biological role of their targets. Increasing knowledge of genomes and the intricate mechanisms that regulate their expression has aroused considerable interest in molecules that target nucleic acids. A wide variety of technologies have been developed based on unnatural oligonucleotides for gene silencing, gene-detection or bio-inspired chemical reactions, for example. In contrast to natural oligonucleotides, their unnatural counterparts can exhibit unique functions based on the chemical reactivity of the accessory molecule. This review focuses on the molecular design of chemically reactive accessory molecules of unnatural oligonucleotides, emphasising their application in specific recognition and reaction toward biological targets.