These dipeptide building blocks containing Ser- or Thr-derived oxazolidines (pseudoprolines) proved to be versatile tools for overcoming some intrinsic problems in the field of peptide chemistry. The presence of pseudoprolines within a peptide sequence results in the disruption of β-sheet structures considered as a source of intermolecular aggregation during chain elongation, thus increasing solvation and coupling kinetics in peptide assembly. Therefore, use of pseudoprolines offer new possibilities for accessing large peptides by convergent strategies and chemoselective ligation techniques. Moreover, incorporation of a pseudoproline unit facilitates cyclization of peptides.