Synthesis and Biological Evaluation of Papain‐Family Cathepsin L‐Like Cysteine Protease Inhibitors Containing a 1,4‐Benzodiazepine Scaffold as Antiprotozoal Agents

Abstract

Novel papain-family cathepsin L-like cysteine protease inhibitors endowed with antitrypanosomal and antimalarial activity were developed, through an optimization study of previously developed inhibitors. In the present work, we studied the structure-activity relationships of these derivatives, with the aim to develop new analogues with a simplified and more synthetically accessible structure and with improved antiparasitic activity. The structure of the model compounds was significantly simplified by modifying or even eliminating the side chain appended at the C3 atom of the benzodiazepine scaffold. In addition, a simple methylene spacer of appropriate length was inserted between the benzodiazepine ring and the 3-bromoisoxazoline moiety. Several rhodesain and falcipain-2 inhibitors displaying single-digit micromolar or sub-micromolar antiparasitic activity against one or both parasites were identified, with activities that were one order of magnitude more potent than the model compounds.

Cathepsin B Inhibitors: Combining Dipeptide Nitriles with an Occluding Loop Recognition Element by Click Chemistry

“…2,3 Further warheads for reversible inhibition of cysteine cathepsins are, for example, peptide aldehydes or ketones, while irreversible inhibition can be achieved with, for example, epoxide derivatives, vinyl sulfones or acyloxymethyl ketones. 2,3,13,14,16,17 Other cathepsin B inhibitor types include nitroxoline derivatives, 6,18 redox-reactive compounds, 19 1,2,4-thiadiazoles, 20 aziridinyl peptides, 21 and cystatin-derived azapeptides. 22 To enhance the selectivity of the broad spectrum cathepsin inhibitor E-64 (II, Figure S1), 23 further epoxysuccinyl derivatives, for example, the highly potent and cathepsin B-selective CA-074 and CA-030 (III and IV, Figure S1) have been developed, binding exclusively to the S1′ and S2′ pockets and exploiting interactions with the positively charged histidine residues of the occluding loop.…”

Development of Novel Benzodiazepine‐Based Peptidomimetics as Inhibitors of Rhodesain from Trypanosoma brucei rhodesiense

“…To synthesize novel peptidomimetics 2 a – g (Scheme ), we first prepared the carboxylic acid 3 and the hPhe synthon 4 according to literature. We then coupled carboxylic acid 3 and ( S )‐5‐phenylpent‐1‐en‐3‐amine 4 in the presence of HOBt and EDCI, as coupling reagent, and DIPEA as a base to obtain the terminal olefin 5 .…”

“…In this medicinal chemistry area, our research team has been involved in the last decade into the development of potent rhodesain inhibitors . In this paper, starting from the structure of the reversible rhodesain inhibitors 1 a – c , endowed with K i values in the low‐micromolar range (Scheme ), we designed a new series of peptidomimetics 2 a – g able to inactivate the target enzyme, considering that an irreversible inhibition is strongly desirable in the case of a parasitic target. In the designed compounds, we maintained the benzodiazepine (BDZ) scaffold as a β‐turn mimetic, which is often suggested as the structural motif of the active form of linear peptides; in addition, this nucleus has optimal oral bioavailability and tolerability, as widely demonstrated by the large use of BDZs as drugs.…”

NMR conformational analysis in solution of a potent class of cysteine proteases inhibitors

“…The synthesis of the inhibitors (±)-1-3, was realized as previously described by our group [21], by treating the benzodiazepine 4 with the bromo-alkenes 5-7, in the presence of sodium hydride, to obtain intermediates 8-10.…”

“…In particular, we focused our attention on the design of peptidomimetics whose use, with respect to peptides, is particularly advantageous in terms of potency and selectivity, as widely demonstrated in these years by our group within the development of protease inhibitors [15][16][17][18][19]. More recently, we developed novel peptidomimetics with a 3-bromoisoxazoline group (IOX) as innovative warhead, able to react with the active site cysteine of rhodesain, thus leading to a reversible inhibition of the target enzyme [20,21]. Promising inhibitors were obtained by coupling a 1,4-benzodiazepine (BDZ) scaffold, a recognition motif widely employed by our group, with IOX, connected by means of an aliphatic chain (AC) of different length (2-4 carbon atoms).…”