New β-phospholactam as a carbapenem transition state analog: Synthesis of a broad-spectrum inhibitor of metallo-β-lactamases

Abstract

In an effort to test whether a transition state analog is an inhibitor of the metallo-β-lactamases, a phospholactam analog of carbapenem has been synthesized and characterized. The phospholactam 1 proved to be a weak, time-dependent inhibitor of IMP-1 (70%), CcrA (70%), L1 (70%), NDM-1 (53%), and Bla2 (94%) at an inhibitor concentration of 100μM. The phospholactam 1 activated ImiS and BcII at the same concentration. Docking studies were used to explain binding and to offer suggestions for modifications to the phospholactam scaffold to improve binding affinities.

Keywords: Inhibitor; Metallo-β-lactamase; Phospholactam.

Figure 1

Structures of β-lactam-containing antibiotics.

Figure 2

Structures of a hypothetical carbapenem transition state and β-phospholactam 1 synthesized in this study.

Figure 3

Complexes of NDM-1 co-crystalized with hydrolyzed β-lactams (A and C) and with the lowest-energy docked β-phospholactam 1 conformation (B and D). The coordinates of NDM-1 in panels A and B as well as hydrolyzed ampicillin in panel A are taken from PDB entry 4HL2. The coordinates of NDM-1 in panels C and D as well as hydrolyzed meropenem in panel C are taken from PDB entry 4EYL. The images were generated with VMD. The protein backbone is shown as a green cartoon and zinc ions as black spheres (Zn₁ on the left and Zn₂ on the right). The β hairpin loop in the back is loop 3; loop 10 was removed for clarity. The hydrolyzed substrates as well as the β-phospholactam 1 inhibitor and the Lys224 side chain are shown as sticks colored by atom (C, gray; O, red, N, blue; S, yellow; P, orange). Key distances summarized in Table 2 are indicated by dashed lines.

Scheme 1

Synthetic route of β-phospholactam 1: a: (1) acetyl chloride, (2) Br₂, (3) MeOH; b: benzylamine, K₂CO₃, CH₃CN; c: NaBH₄, EtOH; d: oxalyl chloride, DMSO, dichloromethane, −78 °C; e: dimethyl phosphonate, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), anhydrous THF; f: NaI, acetone; g: acetic anhydride, pyridine; h: Pd-C, H₂; i: NaH, 15-crown-5, dichloromethane; j: LiOH, H₂O, MeOH.