Side chain homologation of alanyl peptide nucleic acids: pairing selectivity and stacking.

Alanyl peptide nucleic acids (alanyl-PNAs) are oligomers based on a regular peptide backbone with alternating configuration of the amino acids. All side chains are modified by covalently linked nucleobases. Alanyl-PNAs form very rigid, well defined, and linear double strands based on hydrogen bonding of complementary strands, stacking, and solvation. Side chain homology was examined by comparing a methylene linker (alanyl-PNA) with an ethylene linker (homoalanyl-PNA), a trimethylene linker (norvalyl-PNA), and PNA sequences with mixed linker length between nucleobase and backbone. Side chain homology in combination with a linear double strand topology turned out to be valuable in order to selectively manipulate pairing selectivity (pairing mode) and base pair stacking.