Over the past decades, peptide nucleic acid/DNA (PNA:DNA) duplex stability has been improved via backbone modification, often achieved via introducing an amino acid side chain at the Î±- or Î³-position in the PNA sequence. It was previously shown that interstrand cross-linking can further enhance the binding event. In this work, we combined both strategies to fine-tune PNA crosslinking towards single stranded DNA sequences using a furan oxidation-based crosslinking method; for this purpose, Î³-L-lysine and Î³-L-arginine furan-PNA monomers were synthesized and incorporated in PNA sequences via solid phase synthesis. It was shown that the L-lysine Î³-modification had a beneficial effect on crosslink efficiency due to pre-organization of the PNA helix and a favorable electrostatic interaction between the positively-charged lysine and the negatively-charged DNA backbone. Moreover, the crosslink yield could be optimized by carefully choosing the type of furan PNA monomer. This work is the first to describe a selective and biocompatible furan crosslinking strategy for crosslinking of Î³-modified PNA sequences towards single-stranded DNA.
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