Sulfa and trimethoprim-like drugs – antimetabolites acting as carbonic anhydrase,dihydropteroate synthase and dihydrofolate reductase inhibitors

Abstract

Recent advances in microbial genomics, synthetic organic chemistry and X-ray crystallography provided opportunities to identify novel antibacterial targets for the development of new classes of antibiotics and to design more potent antimicrobial compounds derived from existing antibiotics in clinical use for decades. The antimetabolites, sulfa drugs and trimethoprim (TMP)-like agents, are inhibitors of three families of enzymes. One family belongs to the carbonic anhydrases, which catalyze a simple but physiologically relevant reaction in all life kingdoms, carbon dioxide hydration to bicarbonate and protons. The other two enzyme families are involved in the synthesis of tetrahydrofolate (THF), i.e. dihydropteroate synthase (DHPS) and dihydrofolate reductase. The antibacterial agents belonging to the THF and DHPS inhibitors were developed decades ago and present significant bacterial resistance problems. However, the molecular mechanisms of drug resistance both to sulfa drugs and TMP-like inhibitors were understood in detail only recently, when several X-ray crystal structures of such enzymes in complex with their inhibitors were reported. Here, we revue the state of the art in the field of antibacterials based on inhibitors of these three enzyme families.     

N-Sulfamoylphenyl- and N-sulfamoylphenyl-N-thiazolyl-β-alanines and their derivatives as inhibitors of human carbonic anhydrases

A series of N-substituted and N,N-disubstituted β-amino acids and their derivatives bearing benzenesulfonamide moiety were designed and synthesized in search of compounds that would be high-affinity and selective inhibitors of human carbonic anhydrases (CA). There are 12 catalytically active human CA isoforms, the cytosolic CA I, CA II, CA III, CA VII, and CA XIII, secreted CA VI, the mitochondrial CA VA and CA VB, membrane-associated CA IV, and transmembrane CA IX, CA XII, and CA XIV. The di-bromo meta-substituted compounds exhibited low nanomolar dissociation constants and over 10-fold selectivity for mitochondrial isozyme CA VB, implicated in diseases of the central nervous system and obesity. These compounds can be used for further development as inhibitors of significant binding affinity and selectivity towards CA VB isozyme.     

Novel naphthalimide–amino acid conjugates with flexible leucine moiety as side chain: Design,synthesis and potential antitumor activity

A series of novel naphthalimide derivatives with flexible leucine side chains were designed and synthesized. Their antitumor activities were evaluated against HeLa, A549, P388, HL-60, MCF-7, HCT-8 and A375 cancer cell lines in vitro. The preliminary results showed that most of the derivatives had moderate antitumor activities with the IC₅₀ values of 10^?6–10^?5 M. More importantly, compounds 8a–c exhibited exclusive antitumor activities against MCF-7 cell line. The interaction between compound 8b and BSA was also investigated. DNA binding experiments showed that these derivatives behaved as DNA intercalating agents. This work provided a novel class of naphthalimide-based lead compounds with exclusive antitumor activities against MCF-7 cell line for further optimization.     

Structure–activity relationship for enantiomers of potent inhibitors of B. anthracis dihydrofolate reductase

Background: Bacterial resistance to antibiotic therapies is increasing and new treatment options are badly needed. There is an overlap between these resistant bacteria and organisms classified as likely bioterror weapons. For example, Bacillus anthracis is innately resistant to the anti-folate trimethoprim due to sequence changes found in the dihydrofolate reductase enzyme. Development of new inhibitors provides an opportunity to enhance the current arsenal of anti-folate antibiotics while also expanding the coverage of the anti-folate class. Methods: We have characterized inhibitors of B. anthracis dihydrofolate reductase by measuring the K_i and MIC values and calculating the energetics of binding. This series contains a core diaminopyrimidine ring, a central dimethoxybenzyl ring, and a dihydrophthalazine moiety. We have altered the chemical groups extended from a chiral center on the dihydropyridazine ring of the phthalazine moiety. The interactions for the most potent compounds were visualized by X-ray structure determination. Results: We find that the potency of individual enantiomers is divergent with clear preference for the S-enantiomer, while maintaining a high conservation of contacts within the binding site. The preference for enantiomers seems to be predicated largely by differential interactions with protein residues Leu29, Gln30 and Arg53. Conclusions: These studies have clarified the activity of modifications and of individual enantiomers, and highlighted the role of the less-active R-enantiomer in effectively diluting the more active S-enantiomer in racemic solutions. This directly contributes to the development of new antimicrobials, combating trimethoprim resistance, and treatment options for potential bioterrorism agents.     

Synthesis and structure–activity relationship studies of phenolic hydroxyl derivatives based on quinoxalinone as aldose reductase inhibitors with antioxidant activity

To enhance aldose reductase (ALR2) inhibition and add antioxidant ability, phenolic hydroxyl was introduced both to the quinoxalinone core and C3 side chain, resulting in a series of derivatives as ALR2 inhibitors. Biological activity tests suggested that most of the derivatives were potent and selective inhibitors with IC₅₀ values ranging from 0.059 to 6.825 μM, and 2-(3-(4-hydroxystyryl)-7-methoxy-2-oxoquinoxalin-1(2H)-yl)acetic acid (6b) was the most active. Particularly, it was encouraging to find that some derivatives endowed with obvious antioxidant activity, and among them the phenolic 3,4-dihydroxyl compound 6f with 7-hydroxyl in the quinoxalinone core showed the most potent activity, even comparable with the well-known antioxidant Trolox. Structure-activity relationship and docking studies highlighted the importance of phenolic hydroxyl both in C3 side chain and the core structure for constructing potent ALR2 inhibitors with antioxidant activity.     

Design and characterization of alcalase–chitosan conjugates as potential biocatalysts

Bioprocess and Biosystems Engineering - In this study, alcalase (protease from Bacillus licheniformis) immobilization by adsorption, enzyme crosslinking and covalent enzyme binding to activated...     

Synthesis and structure–activity relationships of cassiarin A as potential antimalarials with vasorelaxant activity

Cassiarin A 1, a tricyclic alkaloid, isolated from the leaves of Cassia siamea (Leguminosae), shows powerful antimalarial activity against Plasmodium falciparum in vitro as well as P. berghei in vivo, which may be valuable leads for novel antimalarials. Interactions of parasitized red blood cells (pRBCs) with endothelium in aorta are especially important in the processes contribute to the pathogenesis of severe malaria. Nitric oxide (NO) reduces endothelial expression of receptors/adhesion molecules used by pRBC to adhere to vascular endothelium, and reduces cytoadherence of pRBC to vascular endothelium. Cassiarin A 1 showed vasorelaxation activity against rat aortic ring, which may be related with NO production. A series of a hydroxyl and a nitrogen-substituted derivatives and a dehydroxy derivative of 1 have been synthesized as having potent antimalarials against P. falciparum with vasodilator activity, which may reduce cytoadherence of pRBC to vascular endothelium. Cassiarin A 1 exhibited a potent antimalarial activity and a high selectivity index in vitro, suggesting that the presence of a hydroxyl and a nitrogen atom without any substituents may be important to show antimalarial activity. Relative to cassiarin A, a methoxy derivative showed more potent vasorelaxant activity, although it did not show improvement for inhibition of P. falciparum in vitro. These cassiarin derivatives may be promising candidates as antimalarials with different mode of actions.     

4-Aminopyridine based amide derivatives as dual inhibitors of tissue non-specific alkaline phosphatase and ecto-5′-nucleotidase with potential anticancer activity

Ecto-nucleotidase members i.e., ecto-5′-nucleotidase and alkaline phosphatase, hydrolyze extracellular nucleotides and play an important role in purinergic signaling. Their overexpression are implicated in a variety of pathological states, including immunological diseases, bone mineralization, vascular calcification and cancer, and thus they represent an emerging drug targets. In order to design potent and selective inhibitors, new derivatives of 4-aminopyridine have been synthesized (10a-10m) and their structures were established on the basis of spectral data. The effect of nature and position of substituent was interestingly observed and justified on the basis of their detailed structure activity relationships (SARs) against both families of ecto-nucleotidase. Compound 10a displayed significant inhibition (IC₅₀ ± SEM = 0.25 ± 0.05 µM) that was found ≈168 fold more potent as compared to previously reported inhibitor suramin (IC₅₀ ± SEM = 42.1 ± 7.8 µM). This compound exhibited 6 times more selectivity towards h-TNAP over h-e5′NT. The anticancer potential and mechanism were also established using cell viability assay, flow cytometric analysis and nuclear staining. Molecular docking studies were also carried out to gain insight into the binding interaction of potent compounds within the respective enzyme pockets and herring-sperm DNA.     

Virtual screening reveals allosteric inhibitors of the Toxoplasma gondii thymidylate synthase–dihydrofolate reductase

The parasite Toxoplasma gondii can lead to toxoplasmosis in those who are immunocompromised. To combat the infection, the enzyme responsible for nucleotide synthesis thymidylate synthase–dihydrofolate reductase (TS–DHFR) is a suitable drug target. We have used virtual screening to determine novel allosteric inhibitors at the interface between the two TS domains. Selected compounds from virtual screening inhibited TS activity. Thus, these results show that allosteric inhibition by small drug-like molecules can occur in T. gondii TS–DHFR and pave the way for new and potent species-specific inhibitors.     

Design,synthesis, and structure–activity relationships of pyrazole derivatives as potential FabH inhibitors

Fatty acid biosynthesis is essential for bacterial survival. FabH, β-ketoacyl-acyl carrier protein (ACP) synthase III, is a particularly attractive target, since it is central to the initiation of fatty acid biosynthesis and is highly conserved among Gram-positive and -negative bacteria. Fifty-six 1-acetyl-3,5-diphenyl-4,5-dihydro-(1H)-pyrazole derivatives were synthesized and developed as potent inhibitors of FabH. This inhibitor class demonstrates strong antibacterial activity. Escherichia coli FabH inhibitory assay and docking simulation indicated that the compounds 1-(5-(4-fluorophenyl)-3-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone (12) and 1-(5-(4-chlorophenyl)-3-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone (13) were potent inhibitors of E. coli FabH.     

Synthesis and structure–activity relationship of a novel series of heterocyclic sulfonamide γ-secretase inhibitors

γ-Secretase inhibitors have been shown to reduce the production of β-amyloid, a component of the plaques that are found in brains of patients with Alzheimer’s disease. A novel series of heterocyclic sulfonamide γ-secretase inhibitors that reduce β-amyloid levels in cells is reported. Several examples of compounds within this series demonstrate a higher propensity to inhibit the processing of amyloid precursor protein compared to Notch, an alternative γ-secretase substrate.     

Exploration of thioxothiazolidinone–sulfonate conjugates as a new class of aldehyde/aldose reductase inhibitors: A synthetic and computational investigation

In the present study, the pharmacophore integration methodology provided an efficient access to a new library of thioxothiazolidinone–sulfonate conjugates (8a–r) from easily available synthetic precursors. The approach was excellently high yielding with flexible structural sites for chemical modifications. The designed hybrid scaffolds were assessed for aldehyde/aldose reductase inhibition activities. The results for the in vitro bioassays were promising with the identification of compound 8e as the lead and selective candidate for ALR2 inhibition with an IC₅₀ value of 0.468 ± 0.003 µM as compared to 3.1 ± 0.2 µM for the standard (sorbinil), whereas compound 8o demonstrated high inhibitory potency for both ALR2 and ALR1 enzymes. Molecular modeling analysis of the potent compounds provided further insight into the biological properties where detailed binding mode analysis revealed that the conjugates (8a–r) were found stabilized in the active site of the enzymes through the development of a number of interactions with catalytic residues.     

DNA-binding affinity and anticancer activity of β-carboline–chalcone conjugates as potential DNA intercalators: Molecular modelling and synthesis

A new series of DNA-interactive β-carboline–chalcone conjugates have been synthesized and evaluated for their in vitro cytotoxicity and DNA-binding affinity. It has been observed that most of these new hybrids have shown potent cytotoxic activities on A-549 (lung adenocarcinoma) cell lines with IC₅₀ values lower than 10 μM. The hybrid 7b is more effective against some of the selected cancer cell lines with IC₅₀ values less than 50 μM. In addition, compounds 7e, 7k, 7p–u has displayed significant elevation in ΔT_m of DNA in comparison to Adriamycin, suggesting significant interaction and remarkable DNA stabilization. The DNA intercalation of these new hybrids has been investigated by fluorescence titration, DNA viscosity measurements, molecular docking as well as molecular dynamics and the results are in agreement with the thermal denaturation studies.     

Brucella suis carbonic anhydrases and their inhibitors: Towards alternative antibiotics?

Carbonic anhydrases have started to emerge as new potential antibacterial targets for several pathogens. Two β-carbonic anhydrases, denominated bsCA I and bsCA II, have been isolated and characterized from the bacterial pathogen Brucella suis, the causative agent of brucellosis or Malta fever. These enzymes have been investigated in detail and a wide range of classical aromatic and heteroaromatic sulfonamides as well as carbohydrate-based compounds have been found to inhibit selectively and efficiently Brucella suis carbonic anhydrases. Inhibition of these metalloenzymes constitutes a novel approach for the potential development of new anti-Brucella agents. This review aims at discussing the recent literature on this topic.     

Synthesis and antibacterial activity of catecholate–ciprofloxacin conjugates

The development of an efficient route to obtain artificial siderophore–antibiotic conjugates active against Gram-negative bacteria is crucial. Herein, a practical access to triscatecholate enterobactin analogues linked to the ciprofloxacin along with their antibacterial evaluation are described. Two series of conjugates were obtained with and without a piperazine linker which is known to improve the pharmacokinetics profile of a drug. A monocatecholate–ciprofloxacin conjugate was also synthesized and evaluated. The antibacterial activities against Pseudomonas aeruginosa for some conjugates are related to the iron concentration in the culture medium and seem to depend on the bacterial iron uptake systems.     

Novel benzofuran-based sulphonamides as selective carbonic anhydrases IX and XII inhibitors: synthesis and in vitro biological evaluation

Abstract

Pursuing on our efforts toward searching for efficient hCA IX and hCA XII inhibitors, herein we report the design and synthesis of new sets of benzofuran-based sulphonamides (4a,b, 5a,b, 9a–c, and 10a–d), featuring the zinc anchoring benzenesulfonamide moiety linked to a benzofuran tail via a hydrazine or hydrazide linker. All the target benzofurans were examined for their inhibitory activities toward isoforms hCA I, II, IX, and XII. The target tumour-associated hCA IX and XII isoforms were efficiently inhibited with K _Is spanning in ranges 10.0–97.5 and 10.1–71.8?nM, respectively. Interestingly, arylsulfonehydrazones 9 displayed the best selectivity toward hCA IX and XII over hCA I (SIs: 39.4–250.3 and 26.0–149.9, respectively), and over hCA II (SIs: 19.6–57.1 and 13.0–34.2, respectively). Furthermore, the target benzofurans were assessed for their anti-proliferative activity, according to US-NCI protocol, toward a panel of sixty cancer cell lines. Only benzofurans 5b and 10b possessed selective and moderate growth inhibitory activity toward certain cancer cell lines.     

Exploration of substituted arylpiperazine–tetrazoles as promising dual norepinephrine and dopamine reuptake inhibitors

In the search for potent dual norepinephrine and dopamine reuptake inhibitors, several substituted arylpiperazine–tetrazoles were designed, synthesized and evaluated for their neurotransmitter reuptake inhibitory activities. Various derivatives exhibited selective and strong neurotransmitter reuptake inhibitory activity. In particular, compounds with a three-carbon linker displayed selective and stronger potency than those with two-carbon and four-carbon linkers. Interestingly, six compounds, 9b, 9c, 9d, 9o, 9q and 9u displayed more effective activity than the standard drug, bupropion. The provided SAR data and potent biological activity can offer useful guidelines for designing dual norepinephrine and dopamine reuptake inhibitors as effective therapeutic agents for treatment of several central nervous system diseases.     

Synthesis and structure–activity relationships of C-glycosylated oxadiazoles as inhibitors of glycogen phosphorylase

A series of per-O-benzoylated 5-β-d-glucopyranosyl-2-substituted-1,3,4-oxadiazoles was prepared by acylation of the corresponding 5-(β-d-glucopyranosyl)tetrazole. As an alternative, oxidation of 2,6-anhydro-aldose benzoylhydrazones by iodobenzene I,I-diacetate afforded the same oxadiazoles. 1,3-Dipolar cycloaddition of nitrile oxides to per-O-benzoylated β-d-glucopyranosyl cyanide gave the corresponding 5-β-d-glucopyranosyl-3-substituted-1,2,4-oxadiazoles. The O-benzoyl protecting groups were removed by base-catalyzed transesterification. The 1,3,4-oxadiazoles were practically inefficient as inhibitors of rabbit muscle glycogen phosphorylase b while the 1,2,4-oxadiazoles displayed inhibitory activities in the micromolar range. The best inhibitors were the 5-β-d-glucopyranosyl-3-(4-methylphenyl- and -2-naphthyl)-1,2,4-oxadiazoles (K_i = 8.8 and 11.6 μM, respectively). A detailed analysis of the structure–activity relationships is presented.     

Novel aromatic–polyamine conjugates as cholinesterase inhibitors with notable selectivity toward butyrylcholinesterase

Three types of aromatic–polyamine conjugates (6a–6s) were designed, synthesized and evaluated as potential inhibitors for cholinesterases (ChEs). The results showed that anthraquinone–polyamine conjugates (AQPCs) exhibited the most potent acetylcholinesterase (AChE) inhibitory activity with IC₅₀ values from 1.50 to 11.13 μM. Anthracene–polyamine conjugates (APCs) showed a surprising selectivity (from 76- to 3125-fold) and were most potent at inhibiting butyrylcholinesterase (BChE), with IC₅₀ values from 0.016 to 0.657 μM. A Lineweaver–Burk plot and molecular modeling studies indicated that the representative compounds, 6l and 6k, targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of ChEs. Furthermore, APCs did not affect HepG2 cell viability at the concentration of 100 μM. Consequently, these polyamine conjugates could be thoroughly and systematically studied for the treatment of AD.