Optimization of Subsite Binding to the beta5 Subunit of the Human 20S Proteasome Using Vinyl Sulfones and 2-keto-1,3,4-oxadiazoles: Syntheses and Cellular Properties of Potent, Selective Proteasome Inhibitors

J Med Chem. 2006 May 18;49(10):2953-68. doi: 10.1021/jm058289o.


Beginning with the peptide sequence Cbz-Ile-Glu(OtBu)-Ala-Leu found in PSI (3), a series of vinyl sulfones (VS) were synthesized for evaluation as inhibitors of the chymotrypsin-like activity of the 20S proteasome. Variations at the key P3 position confirmed the importance of a long side chain capped with a hydrophobic group for optimal potency, consistent with a model of binding to the S3 subsite. The tert-butyl glutamic ester initially used at P3 gave plasma unstable, insoluble compounds and was replaced with the better isostere, N-beta-neopentyl asparagine. The inhibitors were shortened by replacing the N-terminal Cbz-isoleucine with a p-tosyl group without loss of potency. Small l-amino acids were used at P2, where d-substitution was not tolerated. The resulting optimized P4-P3-P2 sequence was grafted onto a novel proteasome inhibitor warhead, 2-keto-1,3,4-oxadiazoles (KOD), to produce reversible, subnanomolar proteasome inhibitors that were 1000-fold selective versus cathepsin B (CatB), cathepsin S (CatS), and trypsin-like as well as PGPH-like proteasome activity. A number of compounds in both the VS and the KOD series exhibited growth inhibitory effects against the human prostate cancer cell line PC3 at submicromolar concentrations.

MeSH terms

  • Animals
  • Antineoplastic Agents / chemical synthesis
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacology
  • Cattle
  • Cell Proliferation / drug effects
  • Drug Stability
  • Humans
  • In Vitro Techniques
  • Models, Molecular
  • Oligopeptides / chemical synthesis*
  • Oligopeptides / chemistry
  • Oligopeptides / pharmacology
  • Oxadiazoles / chemical synthesis*
  • Oxadiazoles / chemistry
  • Oxadiazoles / pharmacology
  • Proteasome Endopeptidase Complex / chemistry
  • Proteasome Endopeptidase Complex / metabolism*
  • Proteasome Inhibitors*
  • Protein Subunits / antagonists & inhibitors
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism
  • Solubility
  • Structure-Activity Relationship
  • Sulfones / chemical synthesis*
  • Sulfones / chemistry
  • Sulfones / pharmacology
  • Vinyl Compounds / chemical synthesis*
  • Vinyl Compounds / chemistry
  • Vinyl Compounds / pharmacology


  • Antineoplastic Agents
  • Oligopeptides
  • Oxadiazoles
  • Proteasome Inhibitors
  • Protein Subunits
  • Sulfones
  • Vinyl Compounds
  • Proteasome Endopeptidase Complex