4-Amino-1,2,4-triazole-3-thione as a Promising Scaffold for the Inhibition of Serine and Metallo- β-Lactamases

Abstract

The emergence of bacteria that co-express serine- and metallo- carbapenemases is a threat to the efficacy of the available β-lactam antibiotic armamentarium. The 4-amino-1,2,4-triazole-3-thione scaffold has been selected as the starting chemical moiety in the design of a small library of β-Lactamase inhibitors (BLIs) with extended activity profiles. The synthesised compounds have been validated in vitro against class A serine β-Lactamase (SBLs) KPC-2 and class B1 metallo β-Lactamases (MBLs) VIM-1 and IMP-1. Of the synthesised derivatives, four compounds showed cross-class micromolar inhibition potency and therefore underwent in silico analyses to elucidate their binding mode within the catalytic pockets of serine- and metallo-BLs. Moreover, several members of the synthesised library have been evaluated, in combination with meropenem (MEM), against clinical strains that overexpress BLs for their ability to synergise carbapenems.

Keywords: 4-amino-1,2,4-triazole-3-thione; bacterial resistance; broad-spectrum activity; non-covalent inhibition; structure-based drug design; thione/thiol tautomerism.

Scheme 1

Reagents and conditions: (a) CS₂, H₂O, refl., 3h, 50% yield; (b) formic acid (1 mL per gram of 4), refl., 45 min, 87% yield; (c) aryl carboxaldehyde (1.1 eq.), 35% HCl (cat.), EtOH, refl., 4–12h, yield: 76% (for 2a), 85% (for 2b), 67% (for 2c), 62% (for 2d), 87% (for 2e), 79% (for 2f), 70% (for 2g); (d) NaBH₄ (8 eq.), 80% EtOH (v/v), 0 °C to r.t. 6–24h, yield: 90% (for 1a), 87% (for 1b), 75% (for 1c), 83% (for 1d), 75% (for 1e), 87% (for 1f), 81% (for 1g).

Figure 1

Docking pose of the compounds in VIM-1, IMP-1 and KPC-2. (a–d) Compounds 1d, 1f, 2b and 2g in VIM-1 binding site, respectively. (e–h) Compounds 1d, 1f, 2b and 2g in IMP-1 binding site, respectively. (i–l) Compounds 1d, 1f, 2b and 2g in KPC-2 binding site, respectively. The position originally occupied by the catalytic water wat1 in KPC-2 has been indicated. Even when the water was not retained in the docking simulations, none of the compounds occupied its position, nor was it able to generate valuable contact with it. Proteins are displayed as cartoon (VIM-1, magenta; IMP-1, light blue; KPC-2 dark yellow), zinc atoms are solid grey spheres and their coordination bonds are represented as grey dashed lines. The side chains of the relevant residues are shown as sticks and are labelled accordingly; ligands are depicted in thick, bright-coloured sticks. Hydrogen bonds formed by the ligand with the residues lining the pocket are shown as yellow dashed lines. The catalytic water in KPC-2 is labelled and shown as a red sphere. For clarity, residues have been numbered according to the PDB.