Abstract
Chemically modified nucleobases are thought to be important for therapeutic purposes as well as diagnosing genetic diseases and have been widely involved in research fields such as molecular biology and biochemical studies. Many artificially modified nucleobases, such as methyl, halogen, and aryl modifications of purines at the C8 position and pyrimidines at the C5 position, are widely studied for their biological functions. DNA containing these modified nucleobases can form non-canonical helical structures such as Z-DNA, G-quadruplex, i-motif, and triplex. This review summarizes the synthesis of chemically modified nucleotides: (i) methylation, bromination, and arylation of purine at the C8 position and (ii) methylation, bromination, and arylation of pyrimidine at the C5 position. Additionally, we introduce the non-canonical structures of nucleic acids containing these modifications.
Highlights
In recent years, research on chemical alterations in nucleobases has increased as it is used for therapeutic purposes and the diagnosis of genetic diseases [1,2,3]
The methylation of guanosine at the C8 position remarkably stabilizes the Z-conformation of oligonucleotides under physiological salt conditions [79,85,86]
The carcinogenic adducts used for the substitution of guanosine at the C8 position have a significant influence on Z-DNA formation (Figure 7) [28,89,96,97]
Summary
Research on chemical alterations in nucleobases has increased as it is used for therapeutic purposes and the diagnosis of genetic diseases [1,2,3] These nucleic acid bases can be naturally modified or chemically synthesized. Solvents, agents, and chemical modifications promote non-B conformations of DNA, such as Z-DNA [13,14,15] and G-quadruplex (G4) [16,17,18] This interesting fact about non-canonical structural sequences is correlated with disease-inducing genes and plays a vital role in biological functions. Despite the numerous studies conducted in this field, the roles and conformational properties of non-canonical DNA structures, including syn conformations, are not yet fully understood. This review discusses the synthesis of chemically modified nucleotides and oligo-nucleotides containing modified bases and their effects on the non-canonical structures [24]
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