Fig. 1

The chemical diversity of XNAs. XNAs are often categorized by the component of the nucleotide (sugar, backbone, or base) carrying a modification. Shown here are XNAs discussed in this review, including both those of medical and historical relevance as well as several newly described chemistries. 2′F, 2′-fluoro; 2′OMe, 2′-O-methyl; LNA, locked nucleic acid; FANA, 2′-fluoro arabinose nucleic acid; HNA, hexitol nucleic acid; 2′MOE, 2′-O-methoxyethyl; ribuloNA, (1′-3′)-β-l-ribulo nucleic acid; TNA, α-l-threose nucleic acid; tPhoNA, 3′-2′ phosphonomethyl-threosyl nucleic acid; dXNA, 2′-deoxyxylonucleic acid; PS, phosphorothioate; phNA, alkyl phosphonate nucleic acid; PNA, peptide nucleic acid