Synthesis and Biological Activity of a Series of Potent Fluoromethyl Ketone Inhibitors of Recombinant Human Calpain I

• Published in: Journal of medicinal chemistry Vol. 40; no. 23; pp. 3820 - 3828
• Main Authors: Chatterjee, Sankar, Ator, Mark A, Bozyczko-Coyne, Donna, Josef, Kurt, Wells, Gregory, Tripathy, Rabindranath, Iqbal, Mohamed, Bihovsky, Ron, Senadhi, Shobha E, Mallya, Satish, O'Kane, Teresa M, McKenna, Beth Ann, Siman, Robert, Mallamo, John P
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07-11-1997
• Subjects: Biological and medical sciences; Calpain - antagonists & inhibitors; Calpain - metabolism; Cathepsin B - antagonists & inhibitors; Cathepsin B - metabolism; Cathepsin L; Cathepsins - antagonists & inhibitors; Cathepsins - metabolism; Cysteine Endopeptidases; Cysteine Proteinase Inhibitors - chemical synthesis; Cysteine Proteinase Inhibitors - pharmacology; Dipeptides - chemical synthesis; Dipeptides - pharmacology; Endopeptidases; Humans; Hydrocarbons, Fluorinated - chemical synthesis; Hydrocarbons, Fluorinated - pharmacology; Ketones - chemical synthesis; Ketones - pharmacology; Leukemia, T-Cell - enzymology; Medical sciences; Miscellaneous; Neuropharmacology; Pharmacology. Drug treatments; Recombinant Proteins - metabolism; Tumor Cells, Cultured - drug effects; Human; Cathepsin L; Isoquinoline derivatives; Peptides; Enzyme; Nitrogen heterocycle; Cysteine endopeptidases; Tripeptide; Enzyme inhibitor; Calpain; Haloketone; In vitro; Peptidases; Structure activity relation; Cathepsin B; Bicyclic compound; Dipeptides; Hydrolases; Aromatic compound; Fluorine Organic compounds; Recombinant protein; Chemical synthesis
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm970197e

Calpain I, an intracellular cysteine protease, has been implicated in the neurodegeneration following an episode of stroke. In this paper, we report on a series of potent dipeptide fluoromethyl ketone inhibitors of recombinant human calpain I (rh calpain I). SAR studies revealed that while calpain I tolerates a variety of hydrophobic groups at the P1 site, Leu at P2 is preferred. However, the nature of the N-terminal capping group has a significant effect on the inhibitory activity of this series of compounds. Compound 4e [(1,2,3,4-tetrahydroisoquinolin-2-yl)carbonyl-Leu-d,l-Phe-CH2F], having a tetrahydroisoquinoline containing urea as the N-terminal capping group, is the most potent dipeptide fluoromethyl ketone inhibitor of calpain I (with a second-order rate constant for inactivation of 276 000 M-1 s-1) yet reported; tripeptide 4k (Cbz-Leu-Leu-d,l-Phe-CH2F) is equipotent. A number of compounds presented in this study displayed excellent selectivity for calpain I over cathepsins B and L, two related cysteine proteases. Compounds which exhibited good inhibitory activity in the assay against isolated rh calpain I also inhibited intracellular calpain I in a human cell line. Thus, in an intact cell assay, compounds 4e and 4k inhibited calpain I with IC50 values of 0.2 and 0.1 μM, respectively. Finally, we also disclose the first example of fluorination of a dipeptide enol silyl ether to generate the corresponding dipeptide fluoromethyl ketone.