In addition to the 20 natural L-amino acids, there are many unnatural or non-canonical amino acids that can be incorporated into the sequence of chemically synthesized peptides. There are many different reasons for including unnatural amino acids, for example, such as increasing the affinity, selectivity, and stability of peptide drugs. Another application is the use of unnatural amino acids to induce or stabilize secondary structures (α-helices, β-sheets).

In the solid-phase synthesis process, trifluoroacetic acid (TFA) is typically used to deblock the resulting peptide from the resin.

Chemically synthesized peptides have a free amino group at the N-terminus and a carboxyl group at the C-terminus.

Peptides may be promising therapeutic agents for the treatment of a number of pathologies, but their relatively short half-life in vivo has become a major obstacle to the development of drugs based on them.