cis-Cyclopentyl PNA (cpPNA) as constrained chiral PNA analogues: stereochemical dependence of DNA/RNA hybridizationElectronic Supplementary Information (ESI) available: Experimental procedures for the synthesis of compounds, 1H, 13C NMR, mass spectral data, crystal structural data and melting curves for triplexes. See http://www.rsc.org/suppdata/cc/b3/b317000d/