Peptidkonformationen, 40. Cyclische Hexapeptidanaloge des Thymopoietins Synthese und Konformationsstudien

Design, synthesis, and functionalization of dimeric peptides targeting chemokine receptor CXCR4

The chemokine receptor CXCR4 is a critical regulator of inflammation and immune surveillance, and it is specifically implicated in cancer metastasis and HIV-1 infection. On the basis of the observation that several of the known antagonists remarkably share a C(2) symmetry element, we constructed symmetric dimers with excellent antagonistic activity using a derivative of a cyclic pentapeptide as monomer. To optimize the binding affinity, we investigated the influence of the distance between the monomers and the pharmacophoric sites in the synthesized constructs. The affinity studies in combination with docking computations support a two-site binding model. In a final step, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was introduced as chelator for (radio-)metals, thus allowing to exploit these compounds as a new group of CXCR4-binding peptidic probes for molecular imaging and endoradiotherapeutic purposes. Both the DOTA conjugates and some of their corresponding metal complexes retain good CXCR4 affinity, and one (68)Ga labeled compound was studied as PET tracer.

Cyclization of all-L-Pentapeptides by Means of 1-Hydroxy-7-azabenzotriazole-Derived Uronium and Phosphonium Reagents

Due to their restricted conformational flexibility, cyclic peptides are of great interest in connection with structure-activity relationships, especially the elucidation of bioactive conformations. For linear peptides that do not contain turn structure-inducing amino acid residues, the cyclization reaction may be an inherently improbable or slow process, and side reactions, such as cyclodimerization and epimerization at the C-terminal residue, may dominate. A number of 1-hydroxy-7-azabenzotriazole-based onium salts were examined for cyclization of thymopentin-derived pentapeptides and the results compared with data from more conventional coupling reagents. The azabenzotriazol-derived coupling reagents stood out as being the most effective by far. The cyclizations proceed extremely rapidly, and in contrast to other coupling reagents, C-terminal epimerization was generally less than 10%. C-terminal D-amino acid residues favor the formation of monocyclic pentapeptide rings. A similar effect was observed for cyclization of linear N-methylamino acid-containing peptides, suggesting that reversible amide bond alkylation such as Hmb-modification should be useful in promoting the cyclization of pepitdes devoid of turn-inducing amino acid residues.