The Disobeying 'Soldier': Use of an Achiral Group to Modulate Chiral Induction in PNA Duplexes.

Peptide nucleic acid (PNA) is a synthetic analogue of DNA in which the natural nucleobases A, G, C, and T are linked to an achiral, charge neutral, pseudopeptide backbone. PNA strands can form double helices similar to DNA whose helical sense can be modulated by applying the 'sergeants-and-soldiers' principle. Attachment of a chiral amino acid (sergeant) at the C-terminus of PNA leads to the amplification of chirality of the sergeant onto the achiral PNA monomers (soldiers), resulting in an enantiomeric excess of either left- or right-handed PNA duplexes. In the present study we looked at the effect of an achiral N-terminal terpyridine (soldier) on the helicity of the double helix that contains <small>L</small>-lysine. We have found that terpyridine interferes with the chiral induction effect of the <small>L</small>-lysines, an effect that can be reverted upon coordination of Cu2+ ions to terpyridine.