Although the most common types of secondary structures in proteins are helices and sheets, other types of structures are also formed, such as turns and loops.

Turns play an important role, both structurally and functionally. With regard to the structural aspect, they intervene in the folding of the peptide chain, favouring the formation of a specific tertiary, globular or fibrous structure. With regard to the functional aspect, the turns are mainly located in the region of the proteins most exposed to the environment, and therefore influence various processes, such as molecular and cellular recognition, as well as interactions between peptide structures and non-peptide substrates or receptors. In addition, the turns serve as templates for the design of new drugs, antigens and pesticides.

The serine-proline sequence, in terms of its ability to induce β-turns, is present in proteins that regulate gene expression and DNA binding. In addition, this sequence is recognised as a substrate by numerous kinases, representing a preferential site for protein phosphorylation.

As an application of our work on the synthesis of dihydroxyprolines, we will discuss the ability of the dihydroxyproline-proline domain to induce the formation of β-turns similar to those induced by the serine-proline pair in synthetic peptides. To this end, it is proposed to incorporate the proline-dihydroxyproline dimer (in blue) into peptide II. This novel peptide supports the possibility of formation of hydrogen bonds similar to those of peptide I, which incorporates the serine-proline sequence (in blue).