Chiral PNAs with constrained open-chain backbones.

Chiral open-chain PNAs have been shown to have improved properties in terms of control of helical handedness, DNA affinity, sequence selectivity, and cellular uptake. They can be synthesized either using preformed chiral monomers or by means of a submonomeric strategy. The former is preferred when only a stereogenic center is present at C-5, whereas for PNA-bearing substituents at C-2, the submonomeric approach is preferred, since racemization, generally occurring during the solid-phase synthesis, can be minimized by this procedure. Here we describe the protocols for the synthesis of PNA oligomers containing C-2- or C-5- (or both) modified monomers and a GC method for checking the optical purity of C-2-modified PNAs.