Design, synthesis, and in vitro evaluation of aza-peptide aldehydes and ketones as novel and selective protease inhibitors

J Enzyme Inhib Med Chem. 2020 Dec;35(1):1387-1402. doi: 10.1080/14756366.2020.1781107.


Aza-peptide aldehydes and ketones are a new class of reversible protease inhibitors that are specific for the proteasome and clan CD cysteine proteases. We designed and synthesised aza-Leu derivatives that were specific for the chymotrypsin-like active site of the proteasome, aza-Asp derivatives that were effective inhibitors of caspases-3 and -6, and aza-Asn derivatives that inhibited S. mansoni and I. ricinus legumains. The crystal structure of caspase-3 in complex with our caspase-specific aza-peptide methyl ketone inhibitor with an aza-Asp residue at P1 revealed a covalent linkage between the inhibitor carbonyl carbon and the active site cysteinyl sulphur. Aza-peptide aldehydes and ketones showed no cross-reactivity towards cathepsin B or chymotrypsin. The initial in vitro selectivity of these inhibitors makes them suitable candidates for further development into therapeutic agents to potentially treat multiple myeloma, neurodegenerative diseases, and parasitic infections.

Keywords: Proteasome inhibitor; anticancer; antiparasitic; aza-peptide carbonyls; caspase and legumain inhibitors.

MeSH terms

  • Aldehydes / chemistry
  • Aldehydes / pharmacology*
  • Animals
  • Aza Compounds / chemistry
  • Aza Compounds / pharmacology*
  • Cattle
  • Crystallography, X-Ray
  • Cysteine Endopeptidases / metabolism
  • Dose-Response Relationship, Drug
  • Drug Design*
  • Humans
  • Ketones / chemistry
  • Ketones / pharmacology*
  • Models, Molecular
  • Molecular Structure
  • Peptides / chemistry
  • Peptides / pharmacology*
  • Protease Inhibitors / chemical synthesis
  • Protease Inhibitors / chemistry
  • Protease Inhibitors / pharmacology*
  • Proteasome Endopeptidase Complex / metabolism
  • Structure-Activity Relationship


  • Aldehydes
  • Aza Compounds
  • Ketones
  • Peptides
  • Protease Inhibitors
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex