A series of benzimidazole–benzoxaborole hybrid molecules linked via an amide linker are described that exhibit good in vitro activity against Onchocerca volvulus, a filarial nematode responsible for the disease onchocerciasis, also known as river blindness. The lead identified in this series, 8a (AN8799), was found to have acceptable pharmacokinetic properties to enable evaluation in animal models of human filariasis. Compound 8a was effective in killing Brugia malayi, B. pahangi, and Litomosoides sigmodontis worms present in Mongolian gerbils when dosed subcutaneously as a suspension at 100 mg/kg/day for 14 days but not when dosed orally at 100 mg/kg/day for 28 days. The measurement of plasma levels of 8a at the end of the dosing period and at the time of sacrifice revealed an interesting dependence of activity on the extended exposure for both 8a and the positive control, flubendazole.

Benzoxaboroles are under study as potential new drugs to treat malaria. One benzoxaborole, AN13762, has potent activity and promising features, but its mechanisms of action and resistance are unknown. To gain insights into these mechanisms, we cultured malaria parasites with nonlethal concentrations of AN13762 and generated parasites with varied levels of resistance. Parasites with low-level resistance had mutations in PfPARE, which processes AN13762 into an active metabolite; PfPARE mutations prevented this processing. Parasites with high-level resistance had mutations in any of a number of enzymes, mostly those involved in stress responses. Parasites selected for AN13762 resistance were not resistant to other antimalarials, suggesting novel mechanisms of action and resistance for AN13762, a valuable feature for a new class of antimalarial drugs.

The optimization of a series of benzimidazole–benzoxaborole hybrid molecules linked via a ketone that exhibit good activity against Onchocerca volvulus, a filarial nematode responsible for the disease onchocerciasis, also known as river blindness, is described. The lead identified in this series, 21 (AN15470), was found to have acceptable pharmacokinetic properties to enable an evaluation following oral dosing in an animal model of onchocerciasis. Compound 21was effective in killing worms implanted in Mongolian gerbils when dosed orally as a suspension at 100 mg/kg/day for 14 days but not when dosed orally at 100 mg/kg/day for 7 days.

Novel l-valinate amide benzoxaboroles and analogues were designed and synthesized for a structure-activity-relationship (SAR) investigation to optimize the growth inhibitory activity against Trypanosoma congolense (T. congolense) and Trypanosoma vivax (T. vivax) parasites. The study identified 4-fluorobenzyl (1-hydroxy-7-methyl-1,3-dihydrobenzo[c][1,2]oxaborole-6-carbonyl)-l-valinate (5, AN11736), which showed IC50 values of 0.15 nM against T. congolense and 1.3 nM against T. vivax, and demonstrated 100% efficacy with a single dose of 10 mg/kg against both T. congolense and T. vivax in mouse models of infection (IP dosing) and in the target animal, cattle, dosed intramuscularly. AN11736 has been advanced to early development studies.

There is an urgent need to develop new and safer antitubercular agents that possess a novel mode of action. We synthesized and evaluated a novel series of 3-aminomethyl 4-halogen benzoxaboroles as Mycobacterium tuberculosis (Mtb) leucyl-tRNA synthetase (LeuRS) inhibitors. A number of Mtb LeuRS inhibitors were identified that demonstrated good antitubercular activity with high selectivity over human mitochondrial and cytoplasmic LeuRS. Further evaluation of these Mtb LeuRS inhibitors by in vivo pharmacokinetics (PK) and murine tuberculosis (TB) efficacy models led to the discovery of GSK3036656 (abbreviated as GSK656). This molecule shows potent inhibition of Mtb LeuRS (IC50 = 0.20 μM) and in vitro antitubercular activity (Mtb H37Rv MIC = 0.08 μM). Additionally, it is highly selective for theMtb LeuRS enzyme with IC50 of >300 μM and 132 μM for human mitochondrial LeuRS and human cytoplasmic LeuRS, respectively. In addition, it exhibits remarkable PK profiles and efficacy against Mtb in mouse TB infection models with superior tolerability over initial leads. This compound has been progressed to clinical development for the treatment of tuberculosis. ■ INTRODUCTION Tuberculosis (TB) is a life-threatening infectious disease caused by the bacteria Mycobacterium tuberculosis (Mtb). The World Health Organization (WHO) estimates that one-third of the world’s population is infected with Mtb, resulting in 1.4 million deaths in 2015. In the same year, there were additional 0.4 million people infected with HIV who also died of TB disease. The current treatment for TB infection requires a combination therapy of four front-line drugs rifampin, isoniazid, pyrazinamide, and ethambutol for 6−9 months, often leading to significant side effects and poor patient compliance. In addition, emergence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) has rendered many front-line and second-line drugs ineffective. Furthermore, totally drug-resistant TB (TDR-TB) has recently emerged that is resistant to all clinical drugs. Therefore, there is an urgent need to develop new antitubercular agents that are effective against TB, which possess a novel mode of action that circumvents these resistances. Bedaquiline and delamanid have recently been approved by the Food and Drug Administration (FDA) or the European Medicines Agency (EMA) to treat MDR-TB, representing the first new TB drugs in more than 40 years. Bedaquiline acts by the novel mechanism of mycobacterial adenosine 5′triphosphate (ATP) synthase inhibition, while delamanid is a nitroimidazole derivative that primarily inhibits synthesis of methoxymycolic and ketomycolic acid, which are components of the mycobacterial cell wall. However, bedaquiline has a boxed warning related to possible cardiac toxicity and delamanid (OPC-67683) induces QTc prolongation. In addition there is cross-resistance between clofazimine and bedaquiline as well as some of pre-existing resistance to delamanid. There has been an increased activity toward the discovery of new antitubercular agents. Other TB drug candidates that are in the clinical development include moxifloxacin, sutezolid, SQ109, and Q203 (Figure 1). We recently identified a series of 3-aminomethylbenzoxaboroles that target Mtb LeuRS (1−4, Figure 2). These Mtb LeuRS inhibitors require the boron atom for Mtb LeuRS activity since it forms a bidentate covalent adduct with the terminal nucleotide of tRNA, Ade76. The resulting covalent adduct traps the 3′ end of tRNA in the editing site in a nonproductive complex, inhibiting leucylation and thus protein synthesis. The amino group of the (S)-aminomethyl side chain at C-3 is critical for binding as it makes three hydrogen bonding interactions. An important finding from this work is that 4halogen atom (especially Cl and Br) significantly improves Mtb LeuRS activity, antitubercular activity against Mtb H37Rv, and selectivity against other bacteria. This effort led to the discovery Received: May 5, 2017 Published: September 27, 2017 Article

Carboxamide pyrazinyloxy benzoxaboroles were investigated with the goal to identify a molecule with satisfactory antimalarial activity, physicochemical properties, pharmacokinetic profile, in vivo efficacy, and safety profile. This optimization effort discovered 46, which met our target candidate profile. Compound 46 had excellent activity against cultured Plasmodium falciparum, and in vivo against P. falciparum and P. berghei in infected mice. It exhibited good PK properties in mice, rats, and dogs. It was highly active against the other 11 P. falciparum strains, which are mostly resistant to chloroquine and pyrimethamine. The rapid parasite in vitro reduction and in vivo parasite clearance profile of 46 were similar to those of artemisinin and chloroquine, two rapid-acting antimalarials. It was nongenotoxic in an Ames assay, an in vitro micronucleus assay, and an in vivo rat micronucleus assay when dosed orally up to 2000 mg/kg. The combined properties of this novel benzoxaborole support its progression to preclinical development.

There is an urgent need to develop new and safer antitubercular agents that possess a novel mode of action. We synthesized and evaluated a novel series of 3-aminomethyl 4-halogen benzoxaboroles as Mycobacterium tuberculosis (Mtb) leucyl-tRNA synthetase (LeuRS) inhibitors. A number of Mtb LeuRS inhibitors were identified that demonstrated good antitubercular activity with high selectivity over human mitochondrial and cytoplasmic LeuRS. Further evaluation of these Mtb LeuRS inhibitors by in vivo pharmacokinetics (PK) and murine tuberculosis (TB) efficacy models led to the discovery of GSK3036656 (abbreviated as GSK656). This molecule shows potent inhibition of Mtb LeuRS (IC50 = 0.20 μM) and in vitro antitubercular activity (Mtb H37Rv MIC = 0.08 μM). Additionally, it is highly selective for the Mtb LeuRS enzyme with IC50 of >300 μM and 132 μM for human mitochondrial LeuRS and human cytoplasmic LeuRS, respectively. In addition, it exhibits remarkable PK profiles and efficacy against Mtb in mouse TB infection models with superior tolerability over initial leads. This compound has been progressed to clinical development for the treatment of tuberculosis.

Novel isoxazoline amide benzoxaboroles were designed and synthesized to optimize the ectoparasiticide activity of this chemistry series against ticks and fleas. The study identified an orally bioavailable molecule, (S)-N-((1-hydroxy-3,3-dimethyl-1,3-dihydrobenzo[c][1,2]oxaborol-6-yl)methyl)-2-methyl-4-(5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)benzamide (23), with a favorable pharmacodynamics profile in dogs (Cmax=7.42ng/mL; Tmax=26.0h; terminal half-life t1/2=127h). Compound 23, a development candidate, demonstrated 100% therapeutic effectiveness within 24h of treatment, with residual efficacy of 97% against American dog ticks (Dermacentor variabilis) on day 30 and 98% against cat fleas (Ctenocephalides felis) on day 32 after a single oral dose at 25mg/kg in dogs.

ABSTRACT The recent development and spread of extensively drug-resistant and totally drug-resistant resistant (TDR) strains of Mycobacterium tuberculosis highlight the need for new antitubercular drugs. Protein synthesis inhibitors have played an important role in the treatment of tuberculosis (TB) starting with the inclusion of streptomycin in the first combination therapies. Although parenteral aminoglycosides are a key component of therapy for multidrug-resistant TB, the oxazolidinone linezolid is the only orally available protein synthesis inhibitor that is effective against TB. Here, we show that small-molecule inhibitors of aminoacyl-tRNA synthetases (AARSs), which are known to be excellent antibacterial protein synthesis targets, are orally bioavailable and effective against M. tuberculosis in TB mouse infection models. We applied the oxaborole tRNA-trapping (OBORT) mechanism, which was first developed to target fungal cytoplasmic leucyl-tRNA synthetase (LeuRS), to M. tuberculosis LeuRS. X-ray crystallography was used to guide the design of LeuRS inhibitors that have good biochemical potency and excellent whole-cell activity against M. tuberculosis . Importantly, their good oral bioavailability translates into in vivo efficacy in both the acute and chronic mouse models of TB with potency comparable to that of the frontline drug isoniazid.

A novel series of isoxazoline benzoxaborole small molecules was designed and synthesized for a structure–activity relationship (SAR) investigation to assess the ectoparasiticide activity against ticks and fleas. The study identified an orally bioavailable molecule, (S)-3,3-dimethyl-5-(5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)benzo[c][1,2]oxaborol-1(3H)-ol (38, AN8030), which was long lasting in dogs (t1/2 = 22 days). Compound 38 demonstrated 97.6% therapeutic effectiveness within 24 h of treatment, with residual efficacy of 95.3% against American dog ticks (Dermacentor variabilis) on day 30% and 100% against cat fleas (Ctenocephalides felis) on day 32 after a single oral dose at 50 mg/kg in dogs.

A series of 6-hetaryloxy benzoxaborole compounds was designed and synthesized for a structure-activity relationship (SAR) investigation to assess the changes in antimalarial activity which result from 6-aryloxy structural variation, substituent modification on the pyrazine ring, and optimization of the side chain ester group. This SAR study discovered highly potent 6-(2-(alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles (9, 27-34) with IC50s = 0.2-22 nM against cultured Plasmodium falciparum W2 and 3D7 strains. Compound 9 also demonstrated excellent in vivo efficacy against P. berghei in infected mice (ED90 = 7.0 mg/kg).

Two new isotopically labeled compounds, (carboxy‐13C‐3,3‐2H2)‐7‐(2‐carboxyethyl)‐1,3‐dihydro‐1‐hydroxy‐2,1‐benzoxaborole (2) and (3‐14C)‐7‐(2‐carboxyethyl)‐1,3‐dihydro‐1‐hydroxy‐2,1‐benzoxaborole (3), were designed and synthesized to support the preclinical development studies of a potential new antimalarial agent, 7‐(2‐carboxyethyl)‐1,3‐dihydro‐1‐hydroxy‐2,1‐benzoxaborole (1). Copyright © 2012 John Wiley & Sons, Ltd.

Efficient synthesis is essential for antimalarial therapeutics. A four-step route has been established for the synthesis of 7-(2-carboxyethyl)-1,3-dihydro-1-hydroxy-2,1-benzoxaborole 1 that is a potent new class boron-containing antimalarial agent in preclinical development with IC50=26nM against the malaria parasite Plasmodium falciparum.

A series of new boron-containing benzoxaborole compounds was designed and synthesized for a continuing structure-activity relationship (SAR) investigation to assess the antimalarial activity changes derived from side-chain structural variation, substituent modification on the benzene ring and removal of boron from five-membered oxaborole ring. This SAR study demonstrated that boron is required for the antimalarial activity, and discovered that three fluoro-substituted 7-(2-carboxyethyl)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles (9, 14 and 20) have excellent potencies (IC50 0.026-0.209 mu M) against Plasmodium falciparum. (C) 2011 Elsevier Ltd. All rights reserved.

A series of boron-containing benzoxaborole compounds was designed and synthesized for a structure-activity relationship investigation surrounding 7-(HOOCCH(2)CH(2))-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (1) with the goal of discovering a new antimalarial treatment. Compound 1 demonstrates the best potency (IC(50)=26nM) against Plasmodium falciparum and has good drug-like properties, with low molecular weight (206.00), low ClogP (0.86) and high water solubility (750μg/mL at pH 7).