Qingqing Huang

From Serendipity to Rational Antituberculosis Drug Discovery of Mefloquine-Isoxazole Carboxylic Acid Esters

Both in vitro and in vivo metabolism studies suggested that 5-(2,8-bis(trifluoromethyl)quinolin-4-yloxymethyl)isoxazole-3-carboxylic acid ethyl ester (compound 3) with previously reported antituberculosis activity is rapidly converted to two metabolites 3a and 3b. In order to improve the metabolic stability of this series, chemistry efforts were focused on the modification of the oxymethylene linker of compound 3 in the present study. Compound 9d with an alkene linker was found to be both more metabolically stable and more potent than compound 3, with a minimum inhibitory concentration (MIC) of 0.2 microM and 2.6 microM against replicating and nonreplicating Mycobaterium tuberculosis, respectively. These attributes make 9d an interesting lead compound. A number of modifications were made to the structure of 9d, and a series of active compounds were discovered. Although some neurotoxicity was observed at a high dosage, this new series was endowed with both improved in vitro anti-TB activity and metabolic stability in comparison to compound 3.

Searching for New Cures for Tuberculosis: Design, Synthesis, and Biological Evaluation of 2-Methylbenzothiazoles

The actual development and clinical use of new therapeutics for tuberculosis (TB) have remained stagnant for years because of the complexity of the disease process, the treatment of which at present requires the administration of drug combinations over a 6 month period. There is thus an urgent need for the discovery and development of novel, more active, and less toxic anti-TB agents. In this study, we report on the chemistry and biology of a series of potent 5-(2-methylbenzothiazol-5-yloxymethyl)isoxazole-3-carboxamide derivatives, which proved to be active against replicating Mycobacterium tuberculosis (Mtb) H(37)Rv. The most potent compounds 7j and 7s were found to inhibit Mtb growth at micromolar concentrations, with MIC values of 1.4 and 1.9 microM, respectively. Impressively, all active compounds were nontoxic toward Vero cells (IC(50) > 128 microM). Moreover, the best of these compounds were also tested against protozoan parasites, and some of these compounds were found to show activity, especially against Plasmodium falciparum. These studies thus suggest that certain 2-methylbenzothiazole based compounds may serve as promising lead scaffolds for further elaboration as anti-TB drugs and as possible antimalaria drugs.

Identification, synthesis, and pharmacological evaluation of tetrahydroindazole based ligands as novel antituberculosis agents.

The resurgence of tuberculosis (TB), the incidence of drug-resistant strains of Mycobacterium tuberculosis (MTB), and the coinfection between TB and HIV have led to serious infections, high mortality, and a global health threat, resulting in the urgent search for new classes of antimycobacterial agents. Herein, we report the identification of a novel class of tetrahydroindazole based compounds as potent and unique inhibitors of MTB. Compounds 6a, 6m, and 6q exhibited activity in the low micromolar range against replicating Mycobacterium tuberculosis (R-TB) phenotype, with minimum inhibitory concentrations (MICs) of 1.7, 1.9, and 1.9 muM, respectively, while showing no toxicity to Vero Ccells. Moreover, studies aimed to assess the in vitro metabolic stability of 6a and 6m in mouse liver microsomes and in vivo pharmacokinetic profiles in plasma levels gave satisfactory results. This research suggests that tetrahydroindazole based anti-TB compounds can serve as a promising lead scaffold in developing new drugs to combat tuberculosis infections.

Novel N-Benzoyl-2-hydroxybenzamide Disrupts Unique Parasite Secretory Pathway

ABSTRACT Toxoplasma gondii is a protozoan parasite that can damage the human brain and eyes. There are no curative medicines. Herein, we describe our discovery of N-benzoyl-2-hydroxybenzamides as a class of compounds effective in the low nanomolar range against T. gondii in vitro and in vivo. Our lead compound, QQ-437, displays robust activity against the parasite and could be useful as a new scaffold for development of novel and improved inhibitors of T. gondii. Our genome-wide investigations reveal a specific mechanism of resistance to N-benzoyl-2-hydroxybenzamides mediated by adaptin-3β, a large protein from the secretory protein complex. N-Benzoyl-2-hydroxybenzamide-resistant clones have alterations of their secretory pathway, which traffics proteins to micronemes, rhoptries, dense granules, and acidocalcisomes/plant-like vacuole (PLVs). N-Benzoyl-2-hydroxybenzamide treatment also alters micronemes, rhoptries, the contents of dense granules, and, most markedly, acidocalcisomes/PLVs. Furthermore, QQ-437 is active against chloroquine-resistant Plasmodium falciparum. Our studies reveal a novel class of compounds that disrupts a unique secretory pathway of T. gondii, with the potential to be used as scaffolds in the search for improved compounds to treat the devastating diseases caused by apicomplexan parasites.

Synthesis, Biological Evaluation, and Structure–Activity Relationships of N-Benzoyl-2-hydroxybenzamides as Agents Active against P. falciparum (K1 strain), Trypanosomes, and Leishmania

In our efforts to identify novel chemical scaffolds for the development of new antiprotozoal drugs, a compound library was screened against Toxoplasma gondii tachyzoites with activity discovered for N-(4-ethylbenzoyl)-2-hydroxybenzamide 1a against T. gondii as described elsewhere. Synthesis of a compound set was guided by T. gondii SAR with 1r found to be superior for T. gondii , also active against Thai and Sierra Leone strains of Plasmodium falciparum , and with superior ADMET properties as described elsewhere. Herein, synthesis methods and details of the chemical analysis of the compounds in this series are described. Further, this series of N-benzoyl-2-hydroxybenzamides was repurposed for testing against four other protozoan parasites: Trypanosoma brucei rhodesiense , Trypanosoma cruzi , Leishmania donovani , and P. falciparum (K1 isolate). Structure-activity analyses led to the identification of compounds in this set with excellent antileishmanial activity (compound 1d). Overall, compound 1r was the best and had activity 21-fold superior to that of the standard antimalarial drug chloroquine against the K1 P. falciparum isolate.

Structural analysis of inhibition of E. coli methionine aminopeptidase: implication of loop adaptability in selective inhibition of bacterial enzymes

BackgroundMethionine aminopeptidase is a potential target of future antibacterial and anticancer drugs. Structural analysis of complexes of the enzyme with its inhibitors provides valuable information for structure-based drug design efforts.ResultsFive new X-ray structures of such enzyme-inhibitor complexes were obtained. Analysis of these and other three similar structures reveals the adaptability of a surface-exposed loop bearing Y62, H63, G64 and Y65 (the YHGY loop) that is an integral part of the substrate and inhibitor binding pocket. This adaptability is important for accommodating inhibitors with variations in size. When compared with the human isozymes, this loop either becomes buried in the human type I enzyme due to an N-terminal extension that covers its position or is replaced by a unique insert in the human type II enzyme.ConclusionThe adaptability of the YHGY loop in E. coli methionine aminopeptidase, and likely in other bacterial methionine aminopeptidases, enables the enzyme active pocket to accommodate inhibitors of differing size. The differences in this adaptable loop between the bacterial and human methionine aminopeptidases is a structural feature that can be exploited to design inhibitors of bacterial methionine aminopeptidases as therapeutic agents with minimal inhibition of the corresponding human enzymes.

Stereochemistry at the forefront in the design and discovery of novel anti-tuberculosis agents.

Today, 75% of new drugs introduced to the market are single enantiomers and new techniques in asymmetric synthesis and chiral separation expedites chiral drug discovery and development worldwide. The enantiomers of a chiral drug present unique chemical and pharmacological behaviors in a chiral environment, such as the human body, in which the stereochemistry of chiral drugs determines their pharmacokinetic, pharmacodynamic, and toxicological actions. Thus, it is imperative that only the pure and therapeutically active isomer be prepared and marketed. Tuberculosis (TB), a highly contagious and airborne disease that is caused by infection with Mycobacterium tuberculosis (Mtb), currently represents one of the most threatening health problems globally. The emergence of multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), as well as HIV co-infection along with a lengthy treatment regimen, highlights an urgent need for the development of new anti-TB agents. Currently, new chiral anti-TB agents are being developed from some well-known anti-TB agents, high throughput screening (HTS) hits, and natural products. This review will focus on the reported chiral anti-TB agents together with the clinical importance of their chirality and stereochemistry.