Synthesis of N-Boc and N-Fmoc dipeptoids with nucleobase residues as peptoid nucleic acid monomers

The synthesis of Boc and Fmoc protected peptoid nucleic acid monomers bearing thymine (4a, 4b), adenine (6a, 6b) or guanine (7a, 7b) on the side chain is described. These nucleobases were attached to the amino group of glycine via an ethylene linkage using the Mitsunobu reaction, except cytosine, which was attached using alkylation. After deprotection, these amino acids have been used for synthesizing N-Boc and N-Fmoc dipeptoids.