Conformationally restrained chiral PNA conjugates: synthesis and DNA complementation studies

In recent times, PNA (I), a structural mimic of DNA in which the sugar-phosphate backbone is replaced by N-(2-aminoethyl)glycine (aeg) linkage has emerged as a potential antisense therapeutic agent.<SUP>1</SUP> A major limitation of PNAs from an application perspective is their poor solubility in aqueous medium and being achiral, they bind to cDNA in both parallel (N-PNA/5'-DNA) and antiparallel (N-PNA/3'-DNA) modes. In this connection, we have designed spermine conjugated and conformationally constrained PNA analogues to generate the 4-aminoprolyl backbone (II).<SUP>2</SUP> These were synthesised and evaluated for their DNA binding abilities by using UV and CD spectroscopic studies. It is seen that incorporation of one 4-aminoprolyl unit at the N-terminus of a PNA chain not only enhances the inherent binding of PNA to DNA, but also imparts significant bias in parallel and antiparallel binding with cDNA. Conjugation of spermine at C-terminus enhanced the PNA solubility