Hypoxanthine is an unnatural base that can potentially pair with all natural nucleobases. While hypoxanthine in DNA exhibits marginal preference for pairing with cytosine (C), little is known about its pairing behavior in other DNA analogues. In this study, we synthesized a hypoxanthine-containing monomer and incorporated it into pyrrolidinyl peptide nucleic acid with α/β-peptide backbone derived from D-prolyl-(1S,2S)-2-aminocyclopentanecarboxylic acid (acpcPNA). DNA binding studies clearly revealed that hypoxanthine in acpcPNA behaves like G-analogue because it can specifically form a stable base pair with dC in DNA. The ability to replace G by hypoxanthine without affecting the base pairing properties of acpcPNA can solve a number of problems associated with G-rich acpcPNA including difficult synthesis, formation of secondary structures and fluorescence quenching.
