Discovery of an Orally Available Diazabicyclooctane Inhibitor (ETX0282) of Class A, C, and D Serine β-Lactamases

Abstract

Multidrug resistant Gram-negative bacterial infections are an increasing public health threat due to rapidly rising resistance toward β-lactam antibiotics. The hydrolytic enzymes called β-lactamases are responsible for a large proportion of the resistance phenotype. β-Lactamase inhibitors (BLIs) can be administered in combination with β-lactam antibiotics to negate the action of the β-lactamases, thereby restoring activity of the β-lactam. Newly developed BLIs offer some advantage over older BLIs in terms of enzymatic spectrum but are limited to the intravenous route of administration. Reported here is a novel, orally bioavailable diazabicyclooctane (DBO) β-lactamase inhibitor. This new DBO, ETX1317, contains an endocyclic carbon-carbon double bond and a fluoroacetate activating group and exhibits broad spectrum activity against class A, C, and D serine β-lactamases. The ester prodrug of ETX1317, ETX0282, is orally bioavailable and, in combination with cefpodoxime proxetil, is currently in development as an oral therapy for multidrug resistant and carbapenem-resistant Enterobacterales infections.

Figure 1

Structures of diazabicyclooctane β-lactamase inhibitors.

Figure 2

ETX1317 acyl-enzyme complex with CTX-M-14 β-lactamase. (A) Complex crystal structure of ETX1317 with CTX-M-14 β-lactamase determined at 1.28 Å resolution (PDB code 6VHS). An unbiased F_o – F_c map, shown in green, is contoured at 3σ. The ligand and protein are shown in purple and blue, respectively. Hydrogen bonds between the ligand and protein are depicted as black dashed lines. The catalytic water is shown as a red sphere. (B) Superimposition of ETX1317 with CTX-M-14 (purple/blue) and avibactam with CTX-M-14 (yellow/orange, PDB code 6MZ2, showing only the major conformation of avibactam).

Figure 3

Oral efficacy of the ETX0282/CPDP combination in the neutropenic mouse thigh infection model against the MDR isolate E. coli ARC2687 (AmpC, CTX-M-14). The strain is levofloxacin-resistant (MIC > 4 μg/mL), cefpodoxime-resistant (MIC > 64 μg/mL), meropenem-sensitive (MIC = 0.03 μg/mL), and cefpodoxime/ETX1317-sensitive (MIC = 0.25 μg/mL). Meropenem was dosed subcutaneously (sc, q6h).

Scheme 1. General Synthesis of Diazabicyclooctane Esters and Carboxylic Acids

Scheme 2. Synthesis of ETX0282 and ETX1317: (A) Preparation of the Chiral Bromofluoroacetates and (B) Stereoselective Synthesis of ETX1317 and Its Ester Prodrug ETX0282