Peptides and proteins are natural compounds that play a key role in a number of immune and neurological processes. They act as neurotransmitters, hormones, antigens and antibiotics, and disorders in their function can lead to the development of chronic or infectious diseases. Nevertheless, their use as therapeutics is limited by poor stability and bioavailability. Advances in structural optimization, formulation, and manufacturing are responsible for the growing number of peptides entering clinical trials and therapeutic applications. Furthermore, the need to control peptide function has led to the development of peptidomimetics, compounds that mimic the secondary structures of proteins and thus their functions. Unnatural amino acids play an important role in the synthesis of peptidomimetics. The objective of the research proposed in this master thesis is the synthesis of tripeptides with incorporated unnatural C-glycosyl α-amino acid. Diastereoselective Passerini reactions were used to obtain the C-glycosyl unit. Isopropylidene-protected aldehydes derived from the carbohydrates (sorbose and fructose) were used as the source of the C-glycosyl unit. In the Passerini reaction, amino acid or convertible isocyanide was used, which is very easily removed by the hydrolysis under basic conditions in order to obtain α-hydroxy C-glycosyl acid derivatives. By post-condensation modifications the α-hydroxy derivative was converted to an amino acid, which was incorporated into the dipeptide and tripeptide sequences.