Peptide nucleic acids and their structural modifications

Peptide (polyamide) analogues of nucleic acids (PNAs) make very promising groups of natural nucleic acid (NA) ligands and show many other interesting properties. Two types of these analogues may be highlighted as particularly interesting: the first, containing a polyamide with alternating peptide/pseudopeptide bonds as its backbone, consisting of N-(aminoalkyl)amino-acid units (type I), with nucleobases attached to the backbone nitrogen with the carboxyalkyl linker; and the second, containing a backbone consisting of amino-acid residues carrying the nucleobases in their side chains (type II). So far, these two groups have been studied most intensively. The paper describes main groups of peptide nucleic acids, as well as various other amino acid-derived nucleobase monomers or their oligomers, which were either studied in order to determine their hybridisation to nucleic acids, or only discussed with respect to their potential usefulness in the oligomerisation and nucleic acids binding.