Bts monomers (Bts ; Benzothiazole-2-sulfonyl-) have cyclic backbone (piperazinone) while Fmoc /Boc monomers have linear backbone with Fmoc/Boc protected amine and carboxylic acid at each end. In Bts monomer, Bts group plays an important role not only as a protecting group of amine of backbone but also as an activating group for coupling reaction. Therefore our PNA synthesis does not employ coupling reagents and the excess monomers used in coupling reaction can be easily recovered and re-used if needed.