Research related to boronic acids, from synthetic development to materials to drug discovery, has skyrocketed in the past 20 years. In terms of drug discovery, the incorporation of boronic acids into medicinal chemistry endeavours has seen a steady increase in recent years. In fact, the Food and Drug Administration (FDA) and Health Canada have thus far approved five boronic acid drugs, three of which were approved in the past four years, and several others are in clinical trials. Boronic acids have several desirable properties that has led to their increased use, including potentially enhancing potency of drugs and/or improving their pharmacokinetics profile. This review explores discovery processes of boronic acid drugs. It begins with a brief scope of boron in natural products and in current drugs, followed by an investigation into the various rationalizations for boronic acid incorporation and the synthetic developments that focused on facilitating their addition into organic compounds. We hope that the knowledge we have assembled in this literature review will encourage medicinal chemists to consider the potential benefits of incorporating boronic acids into their future drug discovery endeavours. Contents 1. Introduction 2. Occurrence of boron in nature. Boron in bacteria. Boron in plants. Importance in mammalian systems3. Scope of boronic acid drugs 3.1. Approved boron-containing drugs 3.2. Boron-containing drugs under investigation 3.3. Over-the-counter boron-containing drugs and supplements 3.4. Boron-containing compounds in drug discovery 3.4.1. Anti-cancer boron-containing compounds 3.4.2. Anti-viral boron-containing compounds 3.4.3. Other anti-infective boron-containing compounds 3.4.4. Other therapeutic applications of boron-containing compounds 3.

Severe diseases such as the ongoing COVID-19 pandemic, as well as the previous SARS and MERS outbreaks, are the result of coronavirus infections and have demonstrated the urgent need for antiviral drugs to combat these deadly viruses. Due to its essential role in viral replication and function, 3CL pro (main coronaviruses cysteine-protease) has been identified as a promising target for the development of antiviral drugs. Previously reported SARS-CoV 3CL pro non-covalent inhibitors were used as a starting point for the development of covalent inhibitors of SARS-CoV-2 3CL pro . We report herein our efforts in the design and synthesis of submicromolar covalent inhibitors when the enzymatic activity of the viral protease was used as a screening platform.

Although drug development typically focuses on binding thermodynamics, recent studies suggest that kinetic properties can strongly impact a drug candidate’s efficacy. Robust techniques for measuring inhibitor association and dissociation rates are therefore essential. To address this need, we have developed a pair of complementary isothermal titration calorimetry (ITC) techniques for measuring the kinetics of enzyme inhibition. The advantages of ITC over standard techniques include speed, generality, and versatility; ITC also measures the rate of catalysis directly, making it ideal for quantifying rapid, inhibitor-dependent changes in enzyme activity. We used our methods to study the reversible covalent and non-covalent inhibitors of prolyl oligopeptidase (POP). We extracted kinetics spanning three orders of magnitude, including those too rapid for standard methods, and measured sub-nM binding affinities below the typical ITC limit. These results shed light on the inhibition of POP and demonstrate the general utility of ITC-based enzyme inhibition kinetic measurements.

Over the past decade, there has been an increasing interest in covalent inhibition as a drug design strategy. Our own interest in the development of prolyl oligopeptidase (POP) and fibroblast activation protein α (FAP) covalent inhibitors has led us to question whether these two serine proteases were equal in terms of their reactivity towards electrophilic warheads. To streamline such investigations, we exploited both computational and experimental methods to investigate the influence of different reactive groups on both potency and binding kinetics, using both our own series of POP inhibitors and others' discovered hits. A direct correlation between inhibitor reactivity and residence time was demonstrated through quantum mechanics (QM) methods and further supported by experimental studies. This computational method was also successfully applied to FAP, as an overview of known FAP inhibitors confirmed our computational predictions that more reactive warheads (e.g., boronic acids) must be employed to inhibit FAP than for POP.

Over the past decade, many drug discovery endeavors have been invested in targeting the serine proteases prolyl oligopeptidase (POP) for the treatment of Alzheimer's and Parkinson's disease and, more recently, epithelial cancers. Our research group has focused on the discovery of reversible covalent inhibitors, namely nitriles, to target the catalytic serine residue in this enzyme. While there have been many inhibitors discovered containing a nitrile to covalently bind to the catalytic serine, we have been investigating others, particularly boronic acids and boronic esters, the latter of which have been largely unexplored as covalent warheads. Herein we report a series of computationally-designed POP boronic ester inhibitors. These nanomolar-potent, easilyaccessible (1-2 step syntheses) compounds could facilitate future biochemical and biological studies of this enzyme's role in neurodegenerative diseases and cancer progression.