The synthesis of N-[2-(fluorenylmethoxycarbonyl) aminoethyl]-N-[(2-N-(tert-butoxycarbonyl) isocytosin-5-yl) acetyl] glycine peptide nucleic acid monomer is described. The N-tert- butoxycarbonyl protected monomer is compatible with commercially available monomers designed for the Fmoc-oligomerization strategy and is deprotected under mild acidolysis conditions. Key words: PNA, polyamide, pseudoisocytosine, J-base, triplex.