The preparation of 5-bromouracil and 5-methylcytosine peptide nucleic acid (PNA) monomers is described. These PNA monomers were used for the preparation of several DNA–PNA chimeras and their hybridization properties are described. The substitution of cytosine by 5-methylcytosine in DNA–PNA chimeras increased duplex stability while substitution of thymine by 5-bromouracil maintained it. Moreover, binding of DNA–PNA ...