High-affinity peptide nucleic acid oligomers containing tricyclic cytosine analogues.

[structure: see text] Peptide nucleic acid (PNA) monomers containing the tricyclic cytosine analogues phenoxazine, 9-(2-aminoethoxy)phenoxazine (G-clamp), and 9-(3-aminopropoxy)phenoxazine (propyl-G-clamp) have been synthesized. The modified nucleobases were incorporated into PNA oligomers using Boc-chemistry for solid-phase synthesis. PNAs containing single G-clamp modifications exhibit significantly enhanced affinity toward RNA and DNA targets relative to unmodified PNA while maintaining mismatch discrimination. These PNA G-clamp modifications exhibit the highest increase in affinity toward nucleic acid targets reported so far for PNA modifications.