ABSTRACT
We have designed and evaluated 45 linear analogues of the natural constrained cyclopeptide TMC-95A. These synthetically less demanding molecules are based on the tripeptide sequence Y-N-W of TMC-95A. Structural variations in the amino acid side chains and termini greatly influenced both the efficiency and selectivity of action on a given type of active site. Inhibition constants were submicromolar (Ki approximately 300 nM) despite the absence of the entropically favorable constrained conformation that is characteristic of TMC-95A and its cyclic analogues. These linear compounds were readily prepared and reasonably stable in culture medium and could be optimized to inhibit one, two, or all three proteasome catalytic sites. Cytotoxicity assays performed on a series of human tumor cell lines identified the most potent inhibitors in cells.
Subject(s)
Antineoplastic Agents/chemical synthesis , Peptides, Cyclic/chemical synthesis , Proteasome Inhibitors , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Catalytic Domain , Cell Line, Tumor , Drug Screening Assays, Antitumor , Humans , Peptides, Cyclic/chemistry , Peptides, Cyclic/pharmacology , Structure-Activity RelationshipABSTRACT
The synthesis of three constrained macrocyclic peptide analogues 1 of TMC-95A as potential proteasome inhibitors is described. The key step involves a Ni(0)-mediated macrocyclization of tripeptides 2 bearing halogenated aromatic side chains for the formation of the biaryl junction. In addition, an enantioselective preparation of l-7-bromotryptophan methyl ester 3 using a Corey-O'Donnell alkylation of the glycine benzophenone imine was achieved in good overall yield with very high ee (>85%) on a multigram scale.
