Development of potent chemical antituberculosis agents targeting Mycobacterium tuberculosis acetohydroxyacid synthase

Two maize homologs of mammalian proton-coupled folate transporter, ZmMFS_1-62 and ZmMFS_1-73, are essential to salt and drought tolerance

Folates are essential to the maintenance of normal life activities in almost all organisms. Proton-coupled folate transporter (PCFT), belonging to the major facilitator superfamily, is one of the three major folate transporter types widely studied in mammals. However, information about plant PCFTs is limited. Here, a genome-wide identification of maize PCFTs was performed, and two PCFTs, ZmMFS_1-62 and ZmMFS_1-73, were functionally investigated. Both proteins contained the typical 12 transmembrane helixes with N- and C-termini located in the cytoplasm, and were localized in the plasma membrane. Molecular docking analysis indicated their binding activity with folates via hydrogen bonding. Interference with ZmMFS_1-62 and ZmMFS_1-73 in maize seedlings through virus-induced gene silencing disrupted folate homeostasis, mainly in the roots, and reduced tolerance to drought and salt stresses. Moreover, a molecular chaperone protein, ZmHSP20, was found to interact with ZmMFS_1-62 and ZmMFS_1-73, and interference with ZmHSP20 in maize seedlings also led to folate disruption and increased sensitivity to drought and salt stresses. Overall, this is the first report of functional identification of maize PCFTs, which play essential roles in salt and drought stress tolerance, thereby linking folate metabolism with abiotic stress responses in maize.

Chemical synthesis, biological activities, and molecular simulations of novel sulfonylurea compounds bearing ortho-alkoxy substitutions

A series of 51 novel sulfonylurea compounds with ortho-alkoxy substituent at phenyl ring were chemically synthesized and spectroscopically characterized. The biological activities of the target compounds were evaluated using the enzyme inhibition against acetohydroxyacid synthase (AHAS; EC 2.2.1.6) from fungal or plant source, as well as cell-based antifungal assay and greenhouse pot herbicidal assay. Among the target compounds, 6e showed desirable antifungal activity against Candida albicans standard isolate sc5314 with minimum inhibition concentration (MIC) of 0.39 mg/L (0.98 μM) after 24 h, and 6a demonstrated promising pre-emergence herbicidal activity against Echinochloacrus-galli at 30 g/ha dosage. Representative compounds 6a, 6e, and 6i showed no cell cytotoxicity even at 40 mg/L concentration. Theoretical DFT calculations indicated HOMO maps should be considered to understand the structure-activity relationships. The present study has hence provided useful information for further discovery of novel antifungal agents or selective herbicides.

Advances in Green Catalysis for the Synthesis of Medicinally Relevant N-Heterocycles

N-heterocycles, both saturated and unsaturated, are ubiquitous biologically active molecules that are extremely appealing scaffolds in drug discovery programs. Although classical synthetic methods have been developed to access many relevant N-heterocyclic scaffolds, representing well-established and reliable routes, some do not meet the needs of sustainability. In this context, several advances have been made towards the sustainable synthesis of N-heterocycles. This review focuses on the most recent examples from the last five years of catalytic synthesis of several heterocyclic compounds of medicinal relevance. Thus, the synthesis of isoindoloquinazolines, quinazolines and azaindoles, among others, are covered. The synthetic methods selected include the use of homogeneous and heterogeneous catalysts and the use of alternative and sustainable methods such as, for example, metal-catalyzed acceptorless coupling and one-pot reactions. The green aspects of the individual synthetic approaches are highlighted, and the scope of each methodology is described.

Biochemical and functional characterization of Mycobacterium tuberculosis ketol-acid reductoisomerase

Branched-chain amino acids (BCAAs) are essential amino acids, but their biosynthetic pathway is absent in mammals. Ketol-acid reductoisomerase (IlvC) is a BCAA biosynthetic enzyme that is coded by Rv3001c in Mycobacterium tuberculosis H37Rv (Mtb-Rv) and MRA_3031 in M. tuberculosis H37Ra (Mtb-Ra). IlvCs are essential in Mtb-Rv as well as in Escherichia coli. Compared to wild-type and IlvC-complemented Mtb-Ra strains, IlvC knockdown strain showed reduced survival at low pH and under low pH+starvation stress conditions. Further, increased expression of IlvC was observed under low pH and starvation stress conditions. Confirmation of a role for IlvC in pH and starvation stress was achieved by developing E. coli BL21(DE3) IlvC knockout, which was defective for growth in M9 minimal medium, but growth could be rescued by isoleucine and valine supplementation. Growth was also restored by complementing with over-expressing constructs of Mtb-Ra and E. coli IlvCs. The E. coli knockout also had a survival deficit at pH=5.5 and 4.5 and was more susceptible to killing at pH=3.0. The biochemical characterization of Mtb-Ra and E. coli IlvCs confirmed that both have NADPH-dependent activity. In conclusion, this study demonstrates the functional complementation of E. coli IlvC by Mtb-Ra IlvC and also suggests that IlvC has a role in tolerance to low pH and starvation stress.

Triazolopyrimidine Nuclei: Privileged Scaffolds for Developing Antiviral Agents with a Proper Pharmacokinetic Profile

Viruses are a continuing threat to global health. The lack or limited therapeutic armamentarium against some viral infections and increasing drug resistance issues make the search for new antiviral agents urgent. In recent years, a growing literature highlighted the use of triazolopyrimidine (TZP) heterocycles in the development of antiviral agents, with numerous compounds that showed potent antiviral activities against different RNA and DNA viruses. TZP core represents a privileged scaffold for achieving biologically active molecules, thanks to: i) the synthetic feasibility that allows to variously functionalize TZPs in the different positions of the nucleus, ii) the ability of TZP core to establish multiple interactions with the molecular target, and iii) its favorable pharmacokinetic properties. In the present review, after mentioning selected examples of TZP-based compounds with varied biological activities, we will focus on those antivirals that appeared in the literature in the last 10 years. Approaches used for their identification, the hit-to-lead studies, and the emerged structure-activity relationship will be described. A mention of the synthetic methodologies to prepare TZP nuclei will also be given. In addition, their mechanism of action, the binding mode within the biological target, and pharmacokinetic properties will be analyzed, highlighting the strengths and weaknesses of compounds based on the TZP scaffold, which is increasingly used in medicinal chemistry.

The chemical mechanisms of the enzymes in the branched-chain amino acids biosynthetic pathway and their applications

l-Valine, l-isoleucine, and l-leucine are three key proteinogenic amino acids, and they are also the essential amino acids required for mammalian growth, possessing important and to some extent, special physiological and biological functions. Because of the branched structures in their carbon chains, they are also named as branched-chain amino acids (BCAAs). This review will highlight the advance in studies of the enzymes involved in the biosynthetic pathway of BCAAs, concentrating on their chemical mechanisms and applications in screening herbicides and antibacterial agents. The uses of some of these enzymes in lab scale organic synthesis are also discussed.

Triazolopyrimidinium salts: discovery of a new class of agents for cancer therapy

Aim: The [1,2,4]triazolo[1,5-a]pyrimidine core is highly privileged in medicinal chemistry due to its versatile pharmacological activity profile. Recently, the search for novel anticancer agents has focused on [1,2,4]triazolo[1,5-a]pyrimidine derivatives. Results: Our hit functionalization has led to the discovery of new [1,2,4]triazolo[1,5-a]pyrimidinium salts with potential anticancer activity. Among a small library of molecules, compound 9 significantly inhibits cancer cell growth in a panel of in vitro models. Molecular docking studies and preliminary binding assay have displayed that 9 could directly bind the Src homology 2 (SH2) domain of STAT3 protein. Conclusion: Compound 9 is a novel promising lead compound that motivates additional evaluation of [1,2,4]triazolo[1,5-a]pyrimidinium salts as novel potential chemotherapeutics.

Fluorogenic Assay for Acetohydroxyacid Synthase: Design and Applications

Acetohydroxyacid synthase (AHAS) exists in plants and many microorganisms (including gut flora) but not in mammals, making it an attractive drug target. Fluorescent-based methods should be practical for high-throughput screening of inhibitors. Herein, we describe the development of the first AHAS fluorogenic assay based on an intramolecular charge transfer (ICT)-based fluorescent probe. The assay is facile, sensitive, and continuous and can be applied toward various AHASs from different species, AHAS mutants, and crude cell lysates. The fluorogenic assay was successfully applied for (1) high-throughput screening of commerical herbicides toward different AHASs for choosing matching herbicides, (2) identification of a Soybean AHAS gene with broad-spectrum herbicide resistance, and (3) identification of selective inhibitors toward intestinal-bacterial AHASs. Among the AHAS inhibitors, an active agent was found for selective inhibition of obesity-associated Ruminococcus torques growth, implying the possibility of AHAS inhibitors for the ultimate goal toward antiobesity therapeutics. The fluorogenic assay opens the door for high-throughput programs in AHAS-related fields, and the design principle might be applied for development of fluorogenic assays of other synthases.

1,2,4-Triazolo[1,5-a]pyrimidines in drug design

The 1,2,4-triazolo[1,5-a]pyrimidine (TP) heterocycle, in spite of its relatively simple structure, has proved to be remarkably versatile as evidenced by its use in many different applications reported over the years in different areas of drug design. For example, as the ring system of TPs is isoelectronic with that of purines, this heterocycle has been proposed as a possible surrogate of the purine ring. However, depending on the choice of substituents, the TP ring has also been described as a potentially viable bio-isostere of the carboxylic acid functional group and of the N-acetyl fragment of ε-N-acetylated lysine. In addition, the metal-chelating properties of the TP ring have also been exploited to generate candidate treatments for cancer and parasitic diseases. In the present review article, we discuss recent applications of the TP scaffold in medicinal chemistry, and provide an overview of its properties and methods of synthesis.

Triazolopyrimidine and triazolopyridine scaffolds as TDP2 inhibitors

Tyrosyl-DNA phosphodiesterase 2 (TDP2) repairs topoisomerase II (TOP2) mediated DNA damages and causes cellular resistance to clinically used TOP2 poisons. Inhibiting TDP2 can potentially sensitize cancer cells toward TOP2 poisons. Commercial compound P10A10, to which the structure was assigned as 7-phenyl triazolopyrimidine analogue 6a, was previously identified as a TDP2 inhibitor hit in our virtual and fluorescence-based biochemical screening campaign. We report herein that the hit validation through resynthesis and structure elucidation revealed the correct structure of P10A10 (Chembridge ID 7236827) to be the 5-phenyl triazolopyrimidine regioisomer 7a. Subsequent structure-activity relationship (SAR) via the synthesis of a total of 47 analogues of both the 5-phenyl triazolopyrimidine scaffold (7) and its bioisosteric triazolopyridine scaffold (17) identified four derivatives (7a, 17a, 17e, and 17z) with significant TDP2 inhibition (IC₅₀ < 50 µM), with 17z showing excellent cell permeability and no cytotoxicity.

Chemical preparation, biological evaluation and 3D-QSAR of ethoxysulfuron derivatives as novel antifungal agents targeting acetohydroxyacid synthase

Accetohydroxyacid synthase (AHAS) is the first enzyme involved in the biosynthetic pathway of branched-chain amino acids. Earlier gene mutation of Candida albicans in a mouse model suggested that this enzyme is a promising target of antifungals. Recent studies have demonstrated that some commercial AHAS-inhibiting sulfonylurea herbicides exerted desirable antifungal activity. In this study, we have designed and synthesized 68 novel ethoxysulfulron (ES) derivatives and evaluated their inhibition constants (K_i) against C. albicans AHAS and cell based minimum inhibitory concentration (MIC) values. The target compounds 5-1, 5-10, 5-22, 5-31 and 5-37 displayed stronger AHAS inhibitions than ES did. Compound 5-1 had the best K_i of 6.7 nM against fungal AHAS and MIC values of 2.5 mg/L against Candida albicans and Candica parapsilosis after 72 h. A suitable nematode model was established here and the antifungal activity of 5-1 was further evaluated in vivo. A possible binding mode was simulated via molecular docking and a comparative field analysis (CoMFA) model was constructed to understand the structure-activity relationship. The current study has indicated that some ES derivatives should be considered as promising hits to develop antifungal drugs with novel biological target.

Bacterial Branched-Chain Amino Acid Biosynthesis: Structures, Mechanisms, and Drugability

The eight enzymes responsible for the biosynthesis of the three branched-chain amino acids (l-isoleucine, l-leucine, and l-valine) were identified decades ago using classical genetic approaches based on amino acid auxotrophy. This review will highlight the recent progress in the determination of the three-dimensional structures of these enzymes, their chemical mechanisms, and insights into their suitability as targets for the development of antibacterial agents. Given the enormous rise in bacterial drug resistance to every major class of antibacterial compound, there is a clear and present need for the identification of new antibacterial compounds with nonoverlapping targets to currently used antibacterials that target cell wall, protein, mRNA, and DNA synthesis.

Oxidative dehydrogenation of C-C and C-N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

Nitrogen heteroarenes form an important class of compounds which can be found in natural products, synthetic drugs, building blocks etc. Among the diverse strategies that were developed for the synthesis of nitrogen heterocycles, oxidative dehydrogenation is extremely effective. This review discusses various oxidative dehydrogenation strategies of C-C and C-N bonds to generate nitrogen heteroarenes from their corresponding heterocyclic substrates. The strategies are categorized under stoichiometric and catalytic usage of reagents that facilitate such transformations. The application of these strategies in the synthesis of nitrogen heteroarene natural products and synthetic drug intermediates are also discussed. We hope this review will arouse sufficient interest among the scientific community to further advance the application of oxidative dehydrogenation in the synthesis of nitrogen heteroarenes.

Efficient and regioselective one-step synthesis of 7-aryl-5-methyl- and 5-aryl-7-methyl-2-amino-[1,2,4]triazolo[1,5-a]pyrimidine derivatives

Two facile and efficient one-step procedures for the regioselective synthesis of 7-aryl-5-methyl- and 5-aryl-7-methyl-2-amino-[1,2,4]triazolo[1,5-a]pyrimidines.