Sulfonated analogues of cyclolinopeptide A: Synthesis, immunosuppressive activity and CD studies

Linear and cyclic analogues of cyclolinopeptide A (CLA) in which one or both phenylalanine residues in fragment Pro⁶-Pro⁷-Phe⁸-Phe⁹ were substituted by their sulfonated derivatives have been synthesized by SPPS method and cyclization with the BOP reagent. The peptides were examined for their immunosuppressive activity in the humoral and cellular immune response by PFC and DTH tests. All of the analogues retain some immunosuppressive activity of native CLA. Their CD spectra confirm that the optical activity of aromatic residues in CLA depends on their position in the peptide chain. Only the residue in position 8 seems to be optically active. CD spectrum of the cyclic analogue modified in position 9 is very similar to that of native CLA which correlates with its high biological activity. The chiroptical properties of the p-sulfonated Phe-residue are established.