Synthesis and evaluation of cyclic secondary amine substituted phenyl and benzyl nitrofuranyl amides as novel antituberculosis agents

(NH4)2S2O8 promoted tandem radical cyclization of quinazolin-4(3H)-ones with oxamic acids for the construction of fused quinazolinones under metal-free conditions

A novel cascade radical addition/cyclization reaction of non-activated olefins and oxamic acids has been proposed. Under transition metal-free conditions, 36 quinazolinone derivatives containing an amide moiety were successfully synthesized, with the highest yield being 81%. This method involves the preparation of aminoacyl fused quinazolinone derivatives under mild conditions, offering advantages such as a high yield, a broad substrate compatibility, and a high atom economy.

Persulfate-Promoted Carbamoylation/Cyclization of Alkenes: Synthesis of Amide-Containing Quinazolinones

The incorporation of amide groups into biologically active molecules has been proven to be an efficient strategy for drug design and discovery. In this study, we present a simple and practical method for the synthesis of amide-containing quinazolin-4(3H)-ones under transition-metal-free conditions. This is achieved through a carbamoyl-radical-triggered cascade cyclization of N3-alkenyl-tethered quinazolinones. Notably, the carbamoyl radical is generated in situ from the oxidative decarboxylative process of oxamic acids in the presence of (NH4)2S2O8.

Fluorinated azoles as effective weapons in fight against methicillin-resistance staphylococcus aureus (MRSA) and its SAR studies

The rapid spread of Methicillin-resistant Staphylococcus aureus (MRSA) and its difficult-to-treat skin and filmsy diseases are making MRSA a threat to human life. The most dangerous feature is the fast emergence of MRSA resistance to all recognized antibiotics, including vancomycin. The creation of novel, effective, and non-toxic drug candidates to combat MRSA isolates is urgently required. Fluorine containing small molecules have taken a centre stage in the field of drug development. Over the last 50 years, there have been a growing number of fluorinated compounds that have been approved since the clinical usage of fluorinated corticosteroids in the 1950 s and fluoroquinolones in the 1980 s. Due to its advantages in terms of potency and ADME (absorption, distribution, metabolism, and excretion), fluoro-pharmaceuticals have been regarded as a potent and useful tool in the rational drug design method. The flexible bioactive fluorinated azoles are ideal candidates for the development of new antibiotics. This review summarizes the decade developments of fluorinated azole derivatives with a wide antibacterial activity against diverged MRSA strains. In specific, we correlated the efficacy of structurally varied fluorinated azole analogues including thiazole, benzimidazole, oxadiazole and pyrazole against MRSA and discussed different angles of structure-activity relationship (SAR).

Hydrolytic Activity of Mitochondrial F1FO-ATP Synthase as a Target for Myocardial Ischemia-Reperfusion Injury: Discovery and In Vitro and In Vivo Evaluation of Novel Inhibitors

F1FO-ATP synthase is the mitochondrial complex responsible for ATP production. During myocardial ischemia, it reverses its activity, hydrolyzing ATP and leading to energetic deficit and cardiac injury. We aimed to discover novel inhibitors of ATP hydrolysis, accessing the druggability of the target within ischemia(I)/reperfusion(R) injury. New molecular scaffolds were revealed using ligand-based virtual screening methods. Fifty-five compounds were tested on isolated murine heart mitochondria and H9c2 cells for their inhibitory activity. A pyrazolo[3,4-c]pyridine hit structure was identified and optimized in a hit-to-lead process synthesizing nine novel derivatives. Three derivatives significantly inhibited ATP hydrolysis in vitro, while in vivo, they reduced myocardial infarct size (IS). The novel compound 31 was the most effective in reducing IS, validating that inhibition of F1FO-ATP hydrolytic activity can serve as a target for cardioprotection during ischemia. Further examination of signaling pathways revealed that the cardioprotection mechanism is related to the increased ATP content in the ischemic myocardium and increased phosphorylation of PKA and phospholamban, leading to the reduction of apoptosis.

Discovery and characterization of antimycobacterial nitro-containing compounds with distinct mechanisms of action and in vivo efficacy

Nitro-containing compounds have emerged as important agents in the control of tuberculosis (TB). From a whole-cell high-throughput screen for Mycobacterium tuberculosis (Mtb) growth inhibitors, 10 nitro-containing compounds were prioritized for characterization and mechanism of action studies. HC2209, HC2210, and HC2211 are nitrofuran-based prodrugs that need the cofactor F420 machinery for activation. Unlike pretomanid which depends only on deazaflavin-dependent nitroreductase (Ddn), these nitrofurans depend on Ddn and possibly another F420-dependent reductase for activation. These nitrofurans also differ from pretomanid in their potent activity against Mycobacterium abscessus. Four dinitrobenzamides (HC2217, HC2226, HC2238, and HC2239) and a nitrofuran (HC2250) are proposed to be inhibitors of decaprenyl-phosphoryl-ribose 2'-epimerase 1 (DprE1), based on isolation of resistant mutations in dprE1. Unlike other DprE1 inhibitors, HC2250 was found to be potent against non-replicating persistent bacteria, suggesting additional targets. Two of the compounds, HC2233 and HC2234, were found to have potent, sterilizing activity against replicating and non-replicating Mtb in vitro, but a proposed mechanism of action could not be defined. In a pilot in vivo efficacy study, HC2210 was orally bioavailable and efficacious in reducing bacterial load by ~1 log in a chronic murine TB infection model.

Design, synthesis and biological evaluation of novel oxindole analogs as antitubercular agents

Aim: To design, synthesize and evaluate oxindole derivatives for antitubercular activity. Methodology: We synthesized the derivatives, confirmed their structures by 1H/13C NMR and mass spectrometry, and evaluated them for antitubercular activity against Mycobacterium tuberculosis H37Rv strain using the microplate alamarBlue™ assay. Results: Among all the synthesized derivatives, OXN-1, -3 and -7 exhibited excellent antitubercular activity (minimum inhibitory concentration [MIC]: 0.78 μg/ml). Compounds with a MIC ≤1.56 were tested for cytotoxicity against human embryonic kidney cells and were found to be relatively nontoxic. Molecular docking analysis of OXN-1, -3 and -7 was performed to determine their binding patterns at the active site of DNA topoisomerase II (PDB-5BS8). In drug combination studies, OXN-1, 3 and 7 showed synergism with isoniazid. Conclusion: The obtained results reveal that oxindole derivatives exhibit potent antitubercular activity.

Metal-Free Synthesis of Carbamoylated Chroman-4-Ones via Cascade Radical Annulation of 2-(Allyloxy)arylaldehydes with Oxamic Acids

An efficient and straightforward approach for the synthesis of carbamoylated chroman-4-ones has been well-developed. The reaction is triggered through the generation of carbamoyl radicals from oxamic acids under metal-free conditions, which subsequently undergoes decarboxylative radical cascade cyclization on 2-(allyloxy)arylaldehydes to afford various amide-containing chroman-4-one scaffolds with high functional group tolerance and a broad substrate scope.

Discovery of Potent Small-Molecule USP8 Inhibitors for the Treatment of Breast Cancer through Regulating ERα Expression

Ubiquitin-specific protease 8 (USP8), belonging to the deubiquitinase family, has been implicated to be closely related to the occurrence of many malignant tumors, but only a few USP8-targeting inhibitors have been reported to date. In this study, we present virtual screening to discover novel hit candidates that inhibit the catalytic activity of USP8. Exploration of the structure-activity relationship led to the identification of compound DC-U4106, which binds to USP8 with a K_D value of 4.7 μM and is selective over USP2 and USP7. Western blotting and immunoprecipitation showed that DC-U4106 could target the ubiquitin pathway and facilitate the degradation of ERα. In a xenograft tumor model, DC-U4106 also significantly inhibited tumor growth with minimal toxicity. Overall, our findings suggest that DC-U4106 is a promising drug candidate and targeting the USP8-ERα complex could be a new approach to treat ER-positive or drug-resistant breast cancer.

Design, synthesis and biological evaluation of nitrofuran-1,3,4-oxadiazole hybrids as new antitubercular agents

Three series of novel nitrofuran-1,3,4-oxadiazole hybrids were designed and synthesized as new anti-TB agents. The structure activity relationship study indicated that the linkers and the substituents on the oxadiazole moiety greatly influence the activity, and the substituted benzenes are more favoured than the cycloalkyl or heterocyclic groups. Besides, the optimal compound in series 2 was active against both MTB H₃₇Rv strain and MDR-MTB 16883 clinical isolate and also displayed low cytotoxicity, low inhibition of hERG and good oral PK, indicating its promising potential to be a lead for further structural modifications.

Benzimidazole analogues as efficient arsenals in war against methicillin-resistance staphylococcus aureus (MRSA) and its SAR studies

Small molecule based inhibitors development is a growing field in medicinal chemistry. In recent years, different heterocyclic derivatives have been designed to counter the infections caused by multi-drug resistant bacteria. Indeed, small molecule inhibitors can be employed as an efficient antibacterial agents with different mechanism of action. Methicillin-resistant Staphylococcus aureus (MRSA) is becoming lethal to mankind due to easy transmission mode, rapid resistance development to existing antibiotics and affect difficult-to-treat skin and filmsy diseases. Benzimidazoles are a class of heterocyclic compounds which have capability to fight against MRSA. High biocompatibility of benzimidazoles, synergistic behaviour with antibiotics and their tunable physico-chemical properties attracted the researchers to develop new benzimidazole based antibacterial agents. The present review focus on recent developments of benzimidazole-hybrid molecules as anti MRSA agents and the results of in-vitro and in-vivo studies with possible mechanism of action and discussing structure-activity relationship (SAR) in different directions. Benzimdazoles act as DNA binding agents, enzyme inhibitors, anti-biofilm agents and showed synergistic effect with available antibiotics to achieve antibacterial activity against MRSA. This cumulative figures would help to design new benzimidazole-based MRSA growth inhibitors.

Hybridization Approach to Drug Discovery Inhibiting Mycobacterium tuberculosis-An Overview

Tuberculosis is one of the top 10 causes of death worldwide and the leading cause of death from a single infectious agent, mainly due to Mycobacterium tuberculosis (MTB). Recently, clinical prognoses have worsened due to the emergence of multi-drug resistant (MDR) and extensive-drug resistant (XDR) tuberculosis, which lead to the need for new, efficient and safe drugs. Among the several strategies, polypharmacology could be considered one of the best solutions, in particular, the multitarget directed ligands strategy (MTDLs), based on the synthesis of hybrid ligands acting against two targets of the pathogen. The framework strategy comprises linking, fusing and merging approaches to develop new chemical entities. With these premises, this review aims to provide an overview of the recent hybridization approach, in medicinal chemistry, of the most recent and promising multitargeting antimycobacterial candidates.

New bioactive 5-arylcarboximidamidopyrazolo[3,4-c]pyridines: Synthesis, cytotoxic activity, mechanistic investigation and structure-activity relationships

In this study, a series of novel substituted pyrazolo[3,4-c]pyridin-5-ylamidines was synthesized and their cytotoxicity against three cancer cell lines (MDA-MB-231, HT-1080, PC-3), as well as a human normal cell line (AG01523) was evaluated. A number of derivatives could strongly reduce cancer cells proliferation and exhibit apoptotic induction capability, while reasonable structure-activity relationships could be extracted. Certain analogues were endowed with low toxicity against normal cells. Cell cycle analysis revealed that most of the active compounds induced a G₀/G₁ arrest of HT-1080 cells. Moreover, the potential mechanisms of the cytotoxic activity of the promising compounds were investigated in HT-1080 cells, upon study of their effects on the phosphorylation of Akt, ERK and p38 MAPK. Most of the active derivatives inhibit phosphorylation of Akt and ERK and/or induce p38 MAPK phosphorylation, providing a potential indication on the mode of action of this class.

An appraisal of anti-mycobacterial activity with structure-activity relationship of piperazine and its analogues: A review

Piperazine, is privileged six membered nitrogen containing heterocyclic ring also known as 1,4-Diazacyclohexane. Consequently, piperazine is a versatile medicinally important scaffold and is an essential core in numerous marketed drugs with diverse pharmacological activities. In recent years several potent molecules containing piperazine as an essential subunit of the structural frame have been reported, especially against Mycobacterium tuberculosis (MTB). Remarkably, a good number of these reported molecules also displayed potential activity against multidrug-resistant (MDR), and extremely drug-resistant (XDR) strains of MTB. In this review, we have made a concerted effort to retrace anti-mycobacterial compounds for the past five decades (1971-2019) specifically where piperazine has been used as a vital building block. This review will benefit medicinal chemists as it elaborates on the design, rationale and structure-activity relationship (SAR) of the reported potent piperazine based anti-TB molecules, which in turn will assist them in addressing the gaps, exploiting the reported strategies and developing safer, selective, and cost-effective anti-mycobacterial agents.

Nitromethane as a nitrogen donor in Schmidt-type formation of amides and nitriles

The Schmidt reaction has been an efficient and widely used synthetic approach to amides and nitriles since its discovery in 1923. However, its application often entails the use of volatile, potentially explosive, and highly toxic azide reagents. Here, we report a sequence whereby triflic anhydride and formic and acetic acids activate the bulk chemical nitromethane to serve as a nitrogen donor in place of azides in Schmidt-like reactions. This protocol further expands the substrate scope to alkynes and simple alkyl benzenes for the preparation of amides and nitriles.

Synthesis and biological evaluation of 2,4,5-trisubstituted thiazoles as antituberculosis agents effective against drug-resistant tuberculosis

The dormant and resistant form of Mycobacterium tuberculosis presents a challenge in developing new anti-tubercular drugs. Herein, we report the synthesis and evaluation of trisubstituted thiazoles as antituberculosis agents. The SAR study has identified a requirement of hydrophobic substituent at C2, ester functionality at C4, and various groups with hydrogen bond acceptor character at C5 of thiazole scaffold. This has led to the identification of 13h and 13p as lead compounds. These compounds inhibited the dormant Mycobacterium tuberculosis H37Ra strain and M. tuberculosis H37Rv selectively. Importantly, 13h and 13p were non-toxic to CHO cells. The 13p showed activity against multidrug-resistant tuberculosis isolates.

Current development of 5-nitrofuran-2-yl derivatives as antitubercular agents

Pulmonary tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (MTB) and still remains one of the foremost fatal infectious diseases, infecting nearly a third of the worldwide population. The emergencies of multidrug-resistant and extensively drug-resistant tuberculosis (MDR and XDR-TB) prompt the efforts to deliver potent and novel anti-TB drugs. Research aimed at the development of new anti-TB drugs based on nitrofuran scaffold led to the identification of several candidates that were effective against actively growing as well as latent mycobacteria with unique modes of action. This review focuses on the recent advances in nitrofurans that could provide intriguing potential leads in the area of anti-TB drug discovery.

Optimization of N-benzyl-5-nitrofuran-2-carboxamide as an antitubercular agent

The optimization campaign for a nitrofuran antitubercular hit (N-benzyl-5-nitrofuran-2-carboxamide; JSF-3449) led to the design, synthesis, and biological profiling of a family of analogs. These compounds exhibited potent in vitro antitubercular activity (MIC = 0.019-0.20 μM) against the Mycobacterium tuberculosis H37Rv strain and low in vitro cytotoxicity (CC₅₀ = 40->120 μM) towards Vero cells. Significant improvements in mouse liver microsomal stability and mouse pharmacokinetic profile were realized by introduction of an α, α-dimethylbenzyl moiety. Among these compounds, JSF-4088 is highlighted due to its in vitro antitubercular potency (MIC = 0.019 μM) and Vero cell cytotoxicity (CC₅₀ > 120 μM). The findings suggest a rationale for the continued evolution of this promising series of antitubercular small molecules.

Design, synthesis and evaluation of oxime-functionalized nitrofuranylamides as novel antitubercular agents

A series of oxime-functionalized nitrofuranylamides were designed, synthesized and evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and drug-resistant clinical isolates. Among them, two compounds 7a and 7b exhibited excellent activity against the three tested strains. Both of them were comparable to the first-line anti-TB agents INH and RIF against MTB H37Rv, and were far more potent than INH and RIF against MDR-TB 16833 and 16995 strains. Thus, both of them could act as leads for further optimization.

Fe-Catalyzed tandem cyclization for the synthesis of 3-nitrofurans from homopropargylic alcohols and Al(NO3)3·9H2O

Al(NO3)3·9H2O as a nitro source for the synthesis of 3-nitrofurans from homopropargylic alcohols through Fe-catalyzed tandem cyclization is described. In this transformation, the substituted nitrofurans are obtained through nitration and cyclization. The substrate homopropargylic alcohols with different groups participate smoothly in this process and the desired substituted nitrofurans were obtained in moderate yields.

Synthesis and evaluation of nitrofuranyl methyl N-heterocycles derivatives as novel antitubercular agents

AIM

Tuberculosis (TB) is one of the world's deadliest chronic infectious diseases caused mainly by Mycobacterium tuberculosis (MTB). Many nitrofuran derivatives were found to possess promising anti-TB potential and have been widely studied. In our previous study, we discovered diazaspiro-nitrofuran IMB1701-1702 as potent anti-TB agents.

METHODOLOGY

We report herein a series of nitrofuranyl methyl N-heterocycles based on IMB1701-1702. Results reveal that most of them show potent activity (minimum inhibitory concentration: <0.016-0.062 μg/ml) against MTB H37Rv strain. Especially, compound 7h without cytotoxicity, has the same minimum inhibitory concentration value of ≤0.016 μg/ml as PBTZ169 against both MTB H37Rv strain and two clinically isolated multidrug-resistant MTB strains.

CONCLUSION

The newly designed compound 7h might be a promising anti-TB candidate.

Synthesis, evaluation and CoMFA/CoMSIA study of nitrofuranyl methyl N-heterocycles as novel antitubercular agents

A series of novel nitrofuranyl methyl N-heterocycles based on the structure of IIIM-MCD-211 were designed and synthesized. Compounds 6d, 8b and 12a show excellent activity against MTB H37Rv strain (MIC: 0.031-0.062 μg/mL) roughly comparable to INH and IIIM-MCD-211. In addition, a three-dimensional quantitative structure-activity relationship (3D-QSAR) study was performed on the above mentioned chemical series employing comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) techniques. The developed CoMFA and CoMSIA models display high external predictability (r²_pred of 0.954 and 0.935, respectively) and good statistical robustness. More importantly, the newly designed compounds 16a and 16b (MIC: <0.016 μg/mL) based on the two models, as expected, were found to be more active than 12a and IIIM-MCD-21. Design and synthesis of more potent nitrofuranyl methyl N-heterocycles as anti-TB agents are currently in progress.

Identification of novel 2-aminothiazole conjugated nitrofuran as antitubercular and antibacterial agents

The emergence of antibiotic resistant pathogens is an ongoing main problem in the therapy of bacterial infections. In order to develop promising antitubercular and antibacterial lead compounds, we designed and synthesized a new series of derivatives of 2-aminothiazole conjugated nitrofuran with activities against both Mycobacterium tuberculosis and Staphylococcus aureus. Eight compounds 12e, 12k, 12l, 12m, 18a, 18d, 18e, and 18j emerged as promising antitubercular agents. Structure-activity relationships (SARs) were discussed and showed that the derivatives substituted at the position-3 of benzene of 5-nitro-N-(4-phenylthiazol-2-yl)furan-2-carboxamide exhibited superior potency. The most potent compound 18e, substituted with benzamide at this position, displayed minimum inhibitory concentrations (MICs) of 0.27μg/mL against Mtb H37Ra and 1.36μg/mL against S. aureus. Furthermore, compound 18e had no obvious cytotoxicity to normal Vero cells (IC50=50.2μM). The results suggest that the novel scaffolds of aminothiazole conjugated nitrofuran would be a promising class of potent antitubercular and antimicrobial agents.

A fragment merging approach towards the development of small molecule inhibitors of Mycobacterium tuberculosis EthR for use as ethionamide boosters

With the ever-increasing instances of resistance to frontline TB drugs there is the need to develop novel strategies to fight the worldwide TB epidemic. Boosting the effect of the existing second-line antibiotic ethionamide by inhibiting the mycobacterial transcriptional repressor protein EthR is an attractive therapeutic strategy. Herein we report the use of a fragment based drug discovery approach for the structure-guided systematic merging of two fragment molecules, each binding twice to the hydrophobic cavity of EthR from M. tuberculosis. These together fill the entire binding pocket of EthR. We elaborated these fragment hits and developed small molecule inhibitors which have a 100-fold improvement of potency in vitro over the initial fragments.

Nitrofuranyl Methyl Piperazines as New Anti-TB Agents: Identification, Validation, Medicinal Chemistry, and PK Studies

Whole-cell screening of 20,000 drug-like small molecules led to the identification of nitrofuranyl methylpiperazines as potent anti-TB agents. In the present study, validation followed by medicinal chemistry has been used to explore the structure-activity relationship. Ten compounds demonstrated potent MIC in the range of 0.17-0.0072 μM against H37Rv Mycobacterium tuberculosis (MTB) and were further investigated against nonreplicating and resistant (Rif(R) and MDR) strains of MTB. These compounds were also tested for cytotoxicity. Among the 10 tested compounds, five showed submicromolar to nanomolar potency against nonreplicating and resistant (Rif(R) and MDR) strains of MTB along with a good safety index. Based on their overall in vitro profiles, the solubility and pharmacokinetic properties of five potent compounds were studied, and two analogues, 14f and 16g, were found to have comparatively better solubility than others tested and acceptable pharmacokinetic properties. This study presents the rediscovery of a nitrofuranyl class of compounds with improved aqueous solubility and acceptable oral PK properties, opening a new direction for further development.

Syntheses and Antituberculosis Activity of 1,3-Benzothiazinone Sulfoxide and Sulfone Derived from BTZ043

The discovery of 1,3-benzothiazin-4-ones (BTZs), especially BTZ043 and PBTZ-169 as potent agents for the treatment of tuberculosis, prompted intensive research related to development of potential antituberculosis agents based on electron deficient nitroaromatic scaffolds. Herein we report the syntheses, computational and NMR studies and anti-TB activity of oxidation products, 1,3-benzothiazinone sulfoxide (BTZ-SO) and 1,3-benzothiazinone sulfone (BTZ-SO2) derived from BTZ043. The combined computational and NMR work revealed differences in the total charge densities and molecular shapes of the oxidation products. While docking studies still suggested similar interactions and binding patterns for both products with the target DprE1 enzyme, antituberculosis assays indicated remarkable differences in their activity. Interestingly, BTZ-SO possesses potent activity against nonpathogenic and pathogenic mycobacterial strains, but BTZ-SO2 is only weakly active.

Novel amide and sulphonamide derivatives of 6-(piperazin-1-yl)phenanthridine as potent Mycobacterium tuberculosis H37Rv inhibitors

A series of thirty three novel 6-(piperazin-1-yl)phenanthridine amide and sulphonamide analogues were synthesized, characterized and screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis (MTB) H37Rv strain. These compounds exhibited minimum inhibitory concentration (MIC) between 1.56 and ≥50 μg/mL. Out of these derivatives, few compounds 6l, 6r, 7b, 7f, 7g and 7k exhibited moderate activity (MIC = 6.25 μg/mL) and compounds 6b, 6e, 6k, 6n, 7h, 7i and 7n displayed good activity (MIC = 3.13 μg/mL), whereas compounds 6m, 6s and 7d exhibited excellent anti-tubercular activity (MIC = 1.56 μg/mL). In addition, MTT assay was accomplished on the active analogues of the series against mouse macrophage (RAW 264.7) cells to evaluate the toxicity profile of the newly synthesized compounds and selectivity index of the compounds was determined. Additionally, compounds 6b and 7d were docked to the ATPase domain of M. tuberculosis GyrB protein to know the interaction profile and structures of compounds 6b and 7d were further substantiated through single crystal XRD.

One-pot regioselective synthesis of functionalized and fused furans from Morita–Baylis–Hillman and Rauhut–Currier adducts of nitroalkenes

Functionalized and fused furans were synthesized by a one-pot regioselective cascade reaction from Morita–Baylis–Hillman acetates and Rauhut–Currier adducts of nitroalkenes.

4-Substituted-2,3,5,6-tetrafluorobenzenesulfonamides as inhibitors of carbonic anhydrases I, II, VII, XII, and XIII

A series of 4-substituted-2,3,5,6-tetrafluorobenezenesulfonamides were synthesized and their binding potencies as inhibitors of recombinant human carbonic anhydrase isozymes I, II, VII, XII, and XIII were determined by the thermal shift assay, isothermal titration calorimetry, and stop-flow CO2 hydration assay. All fluorinated benzenesulfonamides exhibited nanomolar binding potency toward tested CAs and fluorinated benzenesulfonamides posessed higher binding potency than non-fluorinated compounds. The crystal structures of 4-[(4,6-dimethylpyrimidin-2-yl)thio]-2,3,5,6-tetrafluorobenzenesulfonamide in complex with CA II and CA XII, and 2,3,5,6-tetrafluoro-4-[(2-hydroxyethyl)sulfonyl]benzenesulfonamide in complex with CA XIII were determined. The observed dissociation constants for several fluorinated compounds reached subnanomolar range for CA I isozyme. The affinity and the selectivity of the compounds towards tested isozymes are presented.

Antitubercular nitrofuran isoxazolines with improved pharmacokinetic properties

A series of tetracyclic nitrofuran isoxazoline anti-tuberculosis agents was designed and synthesized to improve the pharmacokinetic properties of an initial lead compound, which had potent anti-tuberculosis activity but suffered from poor solubility, high protein binding and rapid metabolism. In this study, structural modifications were carried on the outer phenyl and piperidine rings to introduce solubilizing and metabolically blocking functional groups. The compounds generated were evaluated for their in vitro antitubercular activity, bacterial spectrum of activity, solubility, permeability, microsomal stability and protein binding. Pharmacokinetic profiles for the most promising candidates were then determined. Compounds with phenyl morpholine and pyridyl morpholine outer rings were found to be the most potent anti-tuberculosis agents in the series. These compounds retained a narrow antibacterial spectrum of activity, with weak anti-Gram positive and no Gram negative activity, as well as good activity against non-replicating Mycobacterium tuberculosis in a low oxygen model. Overall, the addition of solubilizing and metabolically blocked outer rings did improve solubility and decrease protein binding as designed. However, the metabolic stability for compounds in this series was generally lower than desired. The best three compounds selected for in vivo pharmacokinetic testing all showed high oral bioavailability, with one notable compound showing a significantly longer half-life and good tolerability supporting its further advancement.

Discovery and optimization of benzotriazine di-N-oxides targeting replicating and nonreplicating Mycobacterium tuberculosis

Compounds bactericidal against both replicating and nonreplicating Mtb may shorten the length of TB treatment regimens by eliminating infections more rapidly. Screening of a panel of antimicrobial and anticancer drug classes that are bioreduced into cytotoxic species revealed that 1,2,4-benzotriazine di-N-oxides (BTOs) are potently bactericidal against replicating and nonreplicating Mtb. Medicinal chemistry optimization, guided by semiempirical molecular orbital calculations, identified a new lead compound (20q) from this series with an MIC of 0.31 μg/mL against H37Rv and a cytotoxicity (CC(50)) against Vero cells of 25 μg/mL. 20q also had equivalent potency against a panel of single-drug resistant strains of Mtb and remarkably selective activity for Mtb over a panel of other pathogenic bacterial strains. 20q was also negative in a L5178Y MOLY assay, indicating low potential for genetic toxicity. These data along with measurements of the physiochemical properties and pharmacokinetic profile demonstrate that BTOs have the potential to be developed into a new class of antitubercular drugs.

Design, synthesis, and structure-activity correlations of novel dibenzo[b,d]furan, dibenzo[b,d]thiophene, and N-methylcarbazole clubbed 1,2,3-triazoles as potent inhibitors of Mycobacterium tuberculosis

A molecular hybridization approach is an emerging structural modification tool to design new molecules with improved pharmacophoric properties. In this study, 1,2,3-triazole-based Mycobacterium tuberculosis inhibitors and synthetic and natural product-based tricyclic (carbazole, dibenzo[b,d]furan, and dibenzo[b,d]thiophene) antimycobacterial agents were integrated in one molecular platform to prepare various novel clubbed 1,2,3-triazole hybrids using click chemistry. Structure-activity correlations and in vitro activity against M. tuberculosis strain H37Rv of new analogues revealed the order: dibenzo[b,d]thiophene > dibenzo[b,d]furan > 9-methyl-9H-carbazole series. Two of the most potent M. tuberculosis inhibitors 13h and 13q with MIC = 0.78 μg/mL (∼1.9 μM) displayed a low cytotoxicity and high selectivity index (50-255) against four different human cancer cell lines. These results together provided the potential importance of molecular hybridization and the development of triazole clubbed dibenzo[b,d]thiophene-based lead candidates to treat mycobacterial infections.

One-step syntheses of nitrofuranyl benzimidazoles that are active against multidrug-resistant bacteria

Nitrofuranyl benzimidazoles can be made in one synthetic step from commercially available starting materials. The compounds displayed unexpected antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci with MICs as low as 1 μg ml(-1).

Maximizing bactericidal activity with combinations of bioreduced drugs

Certain antimicrobial and anticancer drugs are only active following bioactivation within the target cell. Nitroimidazoles, nitrofurans and quinoxaline-di-N-oxides represent three chemical classes that are active as anti-tubercular drugs following intracellular bioreduction to reactive intermediates. Two nitroimidazoles are in clinical trials as new anti-tubercular drugs with significant bactericidal activity as well as activity on nonreplicating bacteria. Nitrofurans and quinoxaline-di-N-oxides, which are in preclinical development, also exhibit bactericidal activity and activity on nonreplicating bacteria. Current data indicate these drugs are bioreduced via distinct pathways that yield reactive free radical species. Since flux though each system would become saturated due to enzyme kinetics, cellular uptake or maximum drug concentration attainable in the host, one may propose that using three distinct systems simultaneously could produce a larger burst of free radicals to rapidly and efficiently kill bacteria and shorten the time to cure for tuberculosis. Arguments for the possible development of a novel combination therapy with maximized bacterial cell killing and the possibility of shortening the time to cure will be presented.

Recent advances in the design and synthesis of heterocycles as anti-tubercular agents

Due to the unusual structure and chemical composition of the mycobacterial cell wall, effective tuberculosis (TB) treatment is difficult, making many antibiotics ineffective and hindering the entry of drugs. With approximately 33% of infection, TB is still the second most deadly infectious disease worldwide. The reasons for this are drug-resistant TB (multidrug resistant and extensively drug resistant), persistent infection (latent TB) and synergism of TB with HIV; furthermore no new chemical entity has emerged in last 40 years. New data available from the recently sequenced genome of the mycobacterium and the application of methods of modern drug design promise much for the fight against this disease. In this review, we present an introduction to TB, followed by an overview of new heterocyclic anti-tubercular moieties published during the last decade.