N Boc protected amino acids of analogues of peptide nucleic acid (PNA), which are a class of conformationally constrained building blocks based on 4 aminoproline backbone with chirality at 2 C and 4 C, have been synthesized. Those monomers can be used for the construction of novel peptide nucleic acid analogues. N Boc protected amino acids of analogues of peptide nucleic acid (PNA), which are a class of conformationally constrained building blocks based on 4 aminoproline backbone with chirality at 2 C and 4 C, have been synthesized. Those monomers can be used for the construction of novel peptide nucleic acid analogues.