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.