Synthesis and Evaluation of Macrocyclic Peptide Aldehydes as Potent and Selective Inhibitors of the 20S Proteasome

Abstract

This research explores the first design and synthesis of macrocyclic peptide aldehydes as potent inhibitors of the 20S proteasome. Two novel macrocyclic peptide aldehydes based on the ring-size of the macrocyclic natural product TMC-95 were prepared and evaluated as inhibitors of the 20S proteasome. Both compounds inhibited in the low nanomolar range and proved to be selective for the proteasome over other serine and cysteine proteases, particularly when compared to linear analogues with similar amino acid sequences. In HeLa cells, both macrocycles efficiently inhibited activation of nuclear factor-κB (NF-κB) transcription factor by blocking proteasomal degradation of the inhibitor protein IκBα after cytokine stimulation. Due to their covalent mechanism of binding these compounds represent a 1000-fold increase in inhibitory potency over previously reported noncovalently binding TMC-95 analogues. Molecular modeling of the macrocyclic peptides confirms the preference of the large S 3 pocket for large, hydrophobic residues and the ability to exploit this to improve selectivity of proteasome inhibitors.

The proteasome as a target to combat malaria: hits and misses

“…They further showed that a pulse-treatment (1h) with cyclic peptide-1 blocked progression of the erythrocytic cycle of P. falciparum independent of the stage of the parasite. A subsequent study by Wilson et al shows that a macrocycle added to peptide aldehydes significantly increases selectivity for the proteasome over intracellular cysteine proteases, suggesting the possibility of further improvements to potency and selectivity to cyclic peptide compounds (61).…”

Recent Advances in Macrocyclic Drugs and Microwave-Assisted and/or Solid-Supported Synthesis of Macrocycles

“…Wilson et al reported the solid-phase synthesis and biological evaluation of cyclopeptide aldehydes as potent and selective 20S proteasome inhibitors in 2016 [ 130 ]. The Weinreb amide resin-bound tetrapeptides 150 were cyclized via an intramolecular S N Ar mechanism, followed by the resin cleavage using lithium aluminum hydride (LiAlH 4 ) to provide peptide aldehydes 151 ( Scheme 45 ) [ 130 ]. The biaryl ether macrocycles 151 represent the first macrocyclic peptide aldehydes with high potency (Ki = 54.5 and 241 nM), cellular stability, and specificity for the proteasome.…”

Natural product scaffolds as inspiration for the design and synthesis of 20S human proteasome inhibitors

“…92 Wilson et al later synthesized macrocyclic peptide aldehydes upon the previously established biaryl ether analogues which are nanomolar inhibitors of the ChT-L site. 93 Further efforts to access simplified analogues of TMC-95A have eliminated synthesis of the challenging macrocycle altogether through the development of linear peptide mimics of the natural product. The Vidal group-in collaboration with many other research groups-has used this linear TMC-95A approach to synthesize effective inhibitors.…”