Xeno nucleic acids (XNAs): advances in synthesis, diagnostics, and therapeutics

Xenonucleic acids (XNAs) are defined as sugar-modified nucleic acids, which can be broadly categorized into two groups: those that substitute the ribose or deoxyribose for another sugar or sugar derivative, and those that replace the sugar moiety with a non-sugar unit. These chemical modifications confer enhanced stability, binding affinity, and functional versatility beyond the capabilities of DNA and RNA. This comprehensive review examines the fundamental properties, synthesis methodologies, structural characterization, and biomedical applications of XNAs. Major XNA variants, including locked nucleic acids (LNAs), peptide nucleic acids (PNAs), hexitol nucleic acids (HNAs), fluoro-arabino nucleic acids (FANAs), and morpholino oligomers (MOs), exhibit remarkable nuclease resistance and thermal stability. Synthesis approaches range from traditional phosphoramidite chemistry to enzymatic methods utilizing engineered polymerases and innovative hybrid strategies. Sophisticated characterization techniques, including thermal melting analysis, circular dichroism (CD) spectroscopy, nuclear magnetic resonance (NMR), mass spectrometry (MS), and adapted sequencing methods, enable detailed structural and functional analysis. XNAs have achieved significant clinical impact through FDA-approved antisense therapeutics and revolutionized molecular diagnostics via ultrasensitive liquid biopsy technologies. Current challenges include scalable synthesis, effective delivery systems, and comprehensive structure-function understanding. Future perspectives encompass AI-guided design, synthetic biology applications, and expanded therapeutic pipelines, positioning XNAs as transformative tools in precision medicine and biotechnology.