Method development towards synthesis of carbapenemase inhibitors

Abstract

Carbapenemases are enzymes able to hydrolyze the last resort b-lactam antibiotics (carbapenems), which are used for the treatment of infections caused by resistant bacteria. Carbapenemases are structurally and mechanistically classified into serine-b-lactamases (SBLs) and metallo-b-lactamases (MBLs). In order to combat the hydrolytic activity of these enzymes, combination therapy of b-lactam with b-lactamase inhibitor have been clinically successful. Nevertheless, clinically approved inhibitors for a number of important carbapenemases are still missing and resistance against some of the clinically successful combinations have been already reported. Therefore, there is an urgent need to find new effective inhibitors that could potentially reach clinical use. The approach targeted in this thesis is to design new inhibitors against carbapenemases that could be used in the combination therapy with a carbapenem antibiotic to restore its effect. The goal of my work was to develop synthetic methods for the synthesis of inhibitors targeting two clinically relevant carbapenemases - the serine-b-lactamase oxacillinase 48 (OXA-48) and the metallo-b-lactamase Verona integron-encoded metallo-b-lactamase (VIM-2). For the design and development of inhibitors, a fragment-based approach based on previously discovered inhibitory fragments and structural data of the fragments in complex with the target enzymes was choosen. In this thesis I discuss the developed synthetic strategy towards unsymmetrical 3,5-disubstituted benzoic acids using selective Suzuki-Miyaura cross-coupling. Applying the developed method, I synthesized a small extended fragment library of both symmetrical and unsymmetrical 3,5-disubstituted benzoic acids targeting OXA-48. The aim of synthesizing these extended fragments was to target two directions in the binding pocket as suggested by overlaying structural data of smaller fragments in complex with OXA-48. I also developed a synthetic strategy towards 2-aroylbenzoic acid analogues via carbonylative Suzuki coupling using CO in a safe fashion. 2-Aroylbenzoic acids were known to inhibit the carbapenemase VIM-2. Through my investigations about a general synthetic strategy towards 2-aroylbenzoic acid, I found some limitations about substrates with ionizable functional groups and sterically hindered substrates. I then extended my investigation to find better reaction conditions for carbonylative coupling reactions. I also introduced sustainability to the project by using renewable solvents aiming for better reactivity in palladium-catalyzed C-C, C-O, C-N bond forming carbonylative couplings. In summary, through the presented work a range of carbapenemase (OXA-48 and VIM-2) inhibitors have been synthesized. Additionally, the developed synthetic strategies are considered to be a starting point to build a general approach to synthesize a wide range of potent inhibitors against carbapenemases. The work resulted in three publications (Paper I, II, III).