E‐64c‐Hydrazide: A Lead Structure for the Development of Irreversible Cathepsin C Inhibitors

Abstract

Cathepsin C is a papain-like cysteine protease with dipeptidyl aminopeptidase activity that is thought to activate various granule-associated serine proteases. Its exopeptidase activity is structurally explained by the so-called exclusion domain, which blocks the active-site cleft beyond the S2 site and, with its Asp 1 residue, provides an anchoring point for the N terminus of peptide and protein substrates. Here, the hydrazide of (2S,3S)-trans-epoxysuccinyl-L-leucylamido-3-methylbutane (E-64c) (k2/Ki =140±5 M(-1) s(-1)) is demonstrated to be a lead structure for the development of irreversible cathepsin C inhibitors. The distal amino group of the hydrazide moiety addresses the acidic Asp 1 residue at the entrance of the S2 pocket by hydrogen bonding while also occupying the flat hydrophobic S1'-S2' area with its leucine-isoamylamide moiety. Furthermore, structure-activity relationship studies revealed that functionalization of this distal amino group with alkyl residues can be used to occupy the conserved hydrophobic S2 pocket. In particular, the n-butyl derivative was identified as the most potent inhibitor of the series (k2/Ki =56 000±1700 M(-1) s(-1)).

IL-1 Family Cytokine Pathways Underlying NAFLD: Towards New Treatment Strategies

“…These results strengthen the hypothesis that targeting DPPI might also be an interesting therapeutic approach for NSPs-mediated metabolic diseases. To date, only a few DPPI inhibitors have been described but they were not tested yet in an in-vivo model for NSPs mediated inflammatory diseases (Table 1) (64–66).…”

Solid-Phase Total Synthesis of Dehydrotryptophan-Bearing Cyclic Peptides Tunicyclin B, Sclerotide A, CDA3a, and CDA4a using a Protected β-Hydroxytryptophan Building Block

“…demonstrated that similar epoxides are in fact capable of withstanding 95:5 v/v TFA/H2O. 112 So, we were confident that the global deprotection using TFA could be conducted on the full-length epoxide-containing peptide precursor 3.6. The on-resin cyclization strategy could be applied to the synthesis of CDA3a and CDA4a.…”

“…However, Radzey et al demonstrated that similar epoxides are, in fact, capable of withstanding 95:5 v/v TFA/H 2 O. 19 Keeping this in mind, we decided to adopt an on-resin cyclization strategy of a protected, lipidated peptide, similar to what we used for the total synthesis of daptomycin. 20 The synthesis began with the coupling of Fmoc-D-HOPhGly(OTBS)-OH to the α-NH 2 group of resin-bound dipeptide 12 (Scheme 6).…”

“…The researchers forwent subjecting the protected peptide containing the lipid tail to acidic deprotection conditions due to apprehensions about the epoxide moiety’s stability to acid. However, Radzey et al demonstrated that similar epoxides are, in fact, capable of withstanding 95:5 v/v TFA/H 2 O . Keeping this in mind, we decided to adopt an on-resin cyclization strategy of a protected, lipidated peptide, similar to what we used for the total synthesis of daptomycin …”

Synthetic Approaches of Epoxysuccinate Chemical Probes

“…In addition, an anchoring point for the N terminus of peptide substrates is provided by the Asp‐1 residue. In this context, Schaschke's group [145] reported a series of (2 S ,3 S )‐oxirane‐2,3‐dicarboxylic acid hydrazides 88 (Scheme 16) as inhibitors for cathepsin C. For selectivity studies, a set of Boc protected alkylhydrazines was synthesized and the target compounds were obtained through solution coupling of E‐64c with hydrazines, in presence of TBTU/DIEA, followed by Boc deprotection (Scheme 16). E‐64 hydrazide ( l ‐31 ‐hydrazide) was recognized as a lead compound for development of irreversible cathepsin C inhibitors.…”