Amino acids bearing nucleobases for the synthesis of novel peptide nucleic acids

All of the four nucleobases found in DNA have been incorporated in their protected form into the 4-position of N-tert-butoxycarbonyl-L-proline methyl ester with cis-stereochemistry. An efficient route for the synthesis of N-tert-butoxycarbonyl-trans-4-hydroxy-D-proline methylester has been developed from which the enantiomers may be synthesized, In addition an efficient synthesis of N-tert-butoxycarbonyl-N-(2-hydroxyethyl)glycine methyl ester has been achieved and its hydroxy group replaced with protected nucleobases using the Mitsunobu reaction.