Mycobacterial Targets for Thiourea Derivatives: Opportunities for Virtual Screening in Tuberculosis Drug Discovery

Tuberculosis (TB) remains a primary global health concern, necessitating the discovery and development of new anti-TB drugs, mainly to combat drug-resistant strains. In this context, thiourea derivatives have emerged as promising candidates in TB drug discovery due to their diverse chemical structures and pharmacological properties. This review aimed to explore this potential, identifying and exploring molecular targets for thiourea derivatives in Mycobacterium tuberculosis (Mtb) and the potential application of virtual screening techniques in drug discovery. We have compiled a comprehensive list of possible molecular targets of thiourea derivatives in Mtb. The enzymes are primarily involved in the biosynthesis of various cell wall components, including mycolic acids, peptidoglycans, and arabinans, or targets in the branched-chain amino acid biosynthesis (BCAA) pathway and detoxification mechanisms. We discuss the potential of these targets as critical constituents for the design of novel anti-TB drugs. Besides, we highlight the opportunities that virtual screening methodologies present in identifying potential thiourea derivatives that can interact with these molecular targets. The presented findings contribute to the ongoing efforts in TB drug discovery and lay the foundation for further research in designing and developing more effective treatments against this devastating disease.

Clove Buds Volatile Compounds: Inhibitory Activity on Mycobacterium Growth and Molecular Docking on Mmr Efflux Pump Drug Resistance

Syzygium aromaticum is used in traditional and modern medicine for its various and outstanding pharmacological properties. Here, we studied the chemical composition of hexane extract and non-polar fractions (NPF) obtained from the maceration and fractionation of clove buds, in order to evaluate their in vitro antimycobacterial activity, as well as their contribution against efflux pump (EP) resistance through molecular docking experiments. The gas chromatography-mass spectrometry (GC-MS) analysis of the volatile profiles revealed the presence of eugenol, followed by eugenyl acetate, and β-caryophyllene as common major compounds. According to Resazurin microtiter assay (REMA), Mycobacterium tuberculosis H37 Rv strain was sensitive to all volatile samples at concentration range between 10 and 100 μg/mL. The NPF of ethanol extract was the best inhibitor with a MIC=10 μg/mL. The in silico study revealed a strong binding affinity between eugenol and Mmr EP protein (-8.1 Kcal/mol), involving two binding modes of hydrogen bond and π-alkyl interactions. The non-polarity character of clove volatile constituents, and their potential additive or synergistic effects could be responsible for the antimycobacterial activity. In addition, these findings suggest the benefic effect of eugenol in the management of mycobacterium drug resistance, whether as potential inhibitor of Mmr drug EP, or modulator during combination therapy.

Triad3A involved in the regulation of endotoxin tolerance and mycobactericidal activity through the NFκB-nitric oxide pathway

INTRODUCTION

Sepsis is characterized by an endotoxin tolerance phenotype that occurs in the stage of infection. Persistent bacterial infection can lead to immune cell exhaustion. Triad3A, an E3 ubiquitin ligase, negatively regulates its activation by TLR4. However, the effect of Triad3A on endotoxin tolerance and bactericidal ability in the state of endotoxin tolerance remains unclear.

METHODS

Using single dose LPS and repeated LPS stimulated macrophage cell lines at indicated times, we investigated miR-191, Tirad3A, TRAF3, TLR4, p-P65, TNF-α, IL-1β, and iNOS expression, the effect of miR-191 on Triad3A and TRAF3, gene loss-of-function analyses, the effect of Triad3A on TLR4, p-P65, cytokine, and mycobactericidal activity in endotoxin tolerant cells infected with Mycobacterium marinum.

RESULTS

Here we found that Triad3A is involved in regulating endotoxin tolerance. Our result also displayed that miR-191 expression is downregulated in macrophages in the state of endotoxin tolerance. miR-191 can directly bind to Triad3A and TRAF3. Additionally, knockdown of Triad3A can reverse the effect of decreasing TNF-α and IL-1β in endotoxin tolerant macrophages. Furthermore, we demonstrated that the TLR4-NF-κB-NO pathway was associated with Triad3A and responsible for the killing of intracellular mycobacteria in a tuberculosis sepsis model.

CONCLUSIONS

These results provide new insight into the mechanisms of Triad3A induced tolerogenic phenotype in macrophages, which can help the better comprehension of the pathogenesis involved in septic shock with infection of Mycobacterium tuberculosis, and suggest that Triad3A may be a potential drug target for the treatment of severe septic tuberculosis.

Novel pyrimidine-1,3,4-oxadiazole hybrids and their precursors as potential antimycobacterial agents

Background: Molecular hybridization and isostery are proven approaches in medicinal chemistry, and as such we used them to design novel compounds that we investigated as potential antimycobacterials to combat drug-resistant strains. Methods & results: Prepared N-alkyl-2-(pyrimidine-5-carbonyl)hydrazine-1-carboxamides were cyclized to N-alkyl-5-(pyrimidin-5-yl)-1,3,4-oxadiazol-2-amines along with their analogues. A total of 48 compounds were tested against Mycobacterium tuberculosis H37Rv, Mycobacterium avium and Mycobacterium kansasii, with oxadiazoles and C8-C12 alkyls being the most effective from a concentration of 2 μM. Multidrug-resistant strains were inhibited at same concentrations as the susceptible strain. For the most potent N-dodecyl-5-(pyrimidin-5-yl)-1,3,4-oxadiazol-2-amine, the mechanism of action related to cell wall biosynthesis was investigated. Conclusion: Pyrimidine-1,3,4-oxadiazole hybrids are unique antimycobacterial agents inhibiting mainly M. tuberculosis strains without cross-resistance to current drugs and are thus promising drug candidates.

Synthesis of Novel Benzenesulfonamide-Bearing Functionalized Imidazole Derivatives as Novel Candidates Targeting Multidrug-Resistant Mycobacterium abscessus Complex

Infections caused by drug-resistant (DR) Mycobacterium abscessus (M. abscessus) complex (MAC) are an important public health concern, particularly when affecting individuals with various immunodeficiencies or chronic pulmonary diseases. Rapidly growing antimicrobial resistance among MAC urges us to develop novel antimicrobial candidates for future optimization. Therefore, we have designed and synthesized benzenesulfonamide-bearing functionalized imidazole or S-alkylated derivatives and evaluated their antimicrobial activity using multidrug-resistant M. abscessus strains and compared their antimycobacterial activity using M. bovis BCG and M. tuberculosis H37Ra. Benzenesulfonamide-bearing imidazole-2-thiol compound 13, containing 4-CF₃ substituent in benzene ring, showed strong antimicrobial activity against the tested mycobacterial strains and was more active than some antibiotics used as a reference. Furthermore, an imidazole-bearing 4-F substituent and S-methyl group demonstrated good antimicrobial activity against M. abscessus complex strains, as well as M. bovis BCG and M. tuberculosis H37Ra. In summary, these results demonstrated that novel benzenesulfonamide derivatives, bearing substituted imidazoles, could be further explored as potential candidates for the further hit-to-lead optimization of novel antimycobacterial compounds.

Synthesis, antitubercular evaluation, and molecular docking studies of hybrid pyridinium salts derived from isoniazid

In the quest to develop potent inhibitors for Mycobacterium tuberculosis, novel isoniazid-based pyridinium salts were designed, synthesized, and tested for their antimycobacterial activities against the H₃₇ Rv strain of Mycobacterium tuberculosis using rifampicin as a standard. The pyridinium salts 4k, 4l, and 7d showed exceptional antimycobacterial activities with MIC₉₀ at 1 µg/mL. The in vitro cytotoxicity and pharmacokinetics profiles of these compounds were established for the identification of a lead molecule using in vivo efficacy proof-of-concept studies and found that the lead compound 4k possesses LC₅₀ value at 25 µg/mL. The in vitro antimycobacterial activity results were further supported by in silico studies with good binding affinities ranging from -9.8 to -11.6 kcal/mol for 4k, 4l, and 7d with the target oxidoreductase DprE1 enzyme. These results demonstrate that pyridinium salts derived from isoniazid can be a potentially promising pharmacophore for the development of novel antitubercular candidates.

Improving the antimicrobial activity of old antibacterial drug mafenide: Schiff bases and their bioactivity targeting resistant pathogens

Background: Increasing rates of acquired resistance have justified the critical need for novel antimicrobial drugs. One viable concept is the modification of known drugs. Methods & results: 21 mafenide-based compounds were prepared via condensation reactions and screened for antimicrobial efficacy, which demonstrated promising activity against both Gram-positive and Gram-negative pathogens, pathogenic fungi and mycobacterial strains (minimum inhibitory concentrations from 3.91 μM). Importantly, they retained activity against a panel of superbugs (methicillin- and vancomycin-resistant staphylococci, enterococci, multidrug-resistant Mycobacterium tuberculosis) without any cross-resistance. Unlike mafenide, most of its imines were bactericidal. Toxicity to HepG2 cells was also investigated. Conclusion: Schiff bases were significantly more active than the parent drug, with iodinated salicylidene and 5-nitrofuran/thiophene-methylidene scaffolds being preferred in identifying the most promising drug candidates.

Bioactive Furanyl- or Thienyl-Substituted Nucleobases, Nucleosides and Their Analogues

Five-membered heterocycles, including furan and thiophene, play a prominent role in drug design as structural units of bioactive molecules. This review is intended to demonstrate the importance of the furan-2-yl, furan-3-yl, thien-2-yl and thien-3-yl substituents in the medicinal chemistry of purine and pyrimidine nucleobases, nucleosides and selected analogues. Data presented in the article are limited to compounds containing heteroaromatic ring connected through a bond and not fused to other systems. The impact of bioisosteric replacement of aryl substituents with heteroaryl ones on activities was assessed by comparison of the title compounds with their aryl counterparts. A total of 135 heteroaryl-substituted and 35 aryl-substituted derivatives are mentioned in the text and shown in the figures. The following classes of compounds are included in the article: (i) 5-heteroaryl-2'-deoxyuridines and related compounds; (ii) 8-heteroaryl- 2,9-disubstituted adenine derivatives; (iii) O⁶-(heteroarylmethyl)guanines; (iv) 6-heteroaryl tricyclic guanine analogues; (v) 6-heteroaryl-9-benzylpurines and analogous compounds; (vi) N⁴- furfurylcytosine, N⁶-furfuryladenine, their derivatives and analogues; (vii) 6-heteroaryl purine and 7- deazapurine ribonucleosides; (viii) 7-heteroaryl-7-deazaadenosines, their derivatives and analogues; (ix) 4-heteroaryl fused 7-deazapurine nucleosides. In most cases various modifications of the lead compound structure performed in order to obtain the most favorable activity and selectivity are briefly discussed. The reviewed structure-activity relationship studies exemplify the search for compounds with optimized antiviral, antitumor, antimycobacterial or antiparkinsonian action.

BTZ-Derived Benzisothiazolinones with In Vitro Activity against Mycobacterium tuberculosis

8-Nitro-1,3-benzothiazin-4-ones (BTZs) are known as potent antitubercular agents. BTZ043 as one of the most advanced compounds has reached clinical trials. The putative oxidation products of BTZ043, namely, the corresponding BTZ sulfoxide and sulfone, were reported in this journal (Tiwari et al. ACS Med. Chem Lett. 2015, 6, 128-133). The molecular structures were later revised to the constitutionally isomeric benzisothiazolone and its 1-oxide, respectively. Here, we report two BTZ043-derived benzisothiazolinones (BITs) with in vitro activity against mycobacteria. The constitutionally isomeric O-acyl benzisothiazol-3-ols, in contrast, show little or no antimycobacterial activity in vitro. The structures of the four compounds were investigated by X-ray crystallography and NMR spectroscopy. Molecular covalent docking of the new compounds to Mycobacerium tuberculosis decaprenylphosphoryl-β-d-ribose 2'-epimerase (DprE1) suggests that the active BITs exert antimycobacterial activity through inhibition of DprE1 like BTZs.

Alkaloids of Dicranostigma franchetianum (Papaveraceae) and Berberine Derivatives as a New Class of Antimycobacterial Agents

Tuberculosis (TB) is a widespread infectious disease caused by Mycobacterium tuberculosis. The increasing incidence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains has created a need for new antiTB agents with new chemical scaffolds to combat the disease. Thus, the key question is: how to search for new antiTB and where to look for them? One of the possibilities is to search among natural products (NPs). In order to search for new antiTB drugs, the detailed phytochemical study of the whole Dicranostigma franchetianum plant was performed isolating wide spectrum of isoquinoline alkaloids (IAs). The chemical structures of the isolated alkaloids were determined by a combination of MS, HRMS, 1D, and 2D NMR techniques, and by comparison with literature data. Alkaloids were screened against Mycobacterium tuberculosis H37Ra and four other mycobacterial strains (M. aurum, M. avium, M. kansasii, and M. smegmatis). Alkaloids 3 and 5 showed moderate antimycobacterial activity against all tested strains (MICs 15.625–31.25 µg/mL). Furthermore, ten semisynthetic berberine (16a–16k) derivatives were developed and tested for antimycobacterial activity. In general, the derivatization of berberine was connected with a significant increase in antimycobacterial activity against all tested strains (MICs 0.39–7.81 μg/mL). Two derivatives (16e, 16k) were identified as compounds with micromolar MICs against M. tuberculosis H37Ra (MIC 2.96 and 2.78 µM). All compounds were also evaluated for their in vitro hepatotoxicity on a hepatocellular carcinoma cell line (HepG2), exerting lower cytotoxicity profile than their MIC values, thereby potentially reaching an effective concentration without revealing toxic side effects.

Development of New Antimycobacterial Sulfonyl Hydrazones and 4-Methyl-1,2,3-thiadiazole-Based Hydrazone Derivatives

Fifteen 4-methyl-1,2,3-thiadiazole-based hydrazone derivatives 3a–d and sulfonyl hydrazones 5a–k were synthesized. They were characterized by ¹H-NMR, ¹³C NMR, and HRMS. Mycobacterium tuberculosis strain H37Rv was used to assess their antimycobacterial activity. All compounds demonstrated significant minimum inhibitory concentrations (MIC) from 0.07 to 0.32 µM, comparable to those of isoniazid. The cytotoxicity was evaluated using the standard MTT-dye reduction test against human embryonic kidney cells HEK-293T and mouse fibroblast cell line CCL-1. 4-Hydroxy-3-methoxyphenyl substituted 1,2,3-thiadiazole-based hydrazone derivative 3d demonstrated the highest antimycobacterial activity (MIC = 0.0730 µM) and minimal associated cytotoxicity against two normal cell lines (selectivity index SI = 3516, HEK-293, and SI = 2979, CCL-1). The next in order were sulfonyl hydrazones 5g and 5k with MIC 0.0763 and 0.0716 µM, respectively, which demonstrated comparable minimal cytotoxicity. All compounds were subjected to ADME/Tox computational predictions, which showed that all compounds corresponded to Lipinski’s Ro5, and none were at risk of toxicity. The suitable scores of molecular docking performed on two crystallographic structures of enoyl-ACP reductase (InhA) provide promising insight into possible interaction with the InhA receptor. The 4-methyl-1,2,3-thiadiazole-based hydrazone derivatives and sulfonyl hydrazones proved to be new classes of lead compounds having the potential of novel candidate antituberculosis drugs.

Microwave-assisted organic synthesis, antimycobacterial activity, structure-activity relationship and molecular docking studies of some novel indole-oxadiazole hybrids

Multidrug-resistant tuberculosis (MDR-TB) is a severe threat to mankind because most drugs are ineffective in inhibiting tubercular strains. Due to the increase of MDR-TB, many first and second-line drugs are ineffective against tubercular strains. To combat the resistance of currently accessible drugs, structural changes must be made on a regular basis. Thus, in the search for new antimycobacterial drugs, a series of 1-(2-(1H-indol-3-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl)-3-phenylprop-2-en-1-ones (5a-o) have been developed, synthesized, characterized, and screened for antimycobacterial activity. The synthetic approach includes imine generation and cyclization using both conventional and microwave methods to create hybrid molecules with indole and oxadiazole motifs. The set of synthesized compounds have demonstrated some promising activity against tubercular strains of Mycobacterium tuberculosis (ATCC 25177) and M. bovis (ATCC 35734). Compound 5l inhibited M. bovis strain 100% in 10 µg/mL concentration, while compound 5m inhibited M. tuberculosis strain 90.4% in 30 µg/mL concentration. Molecular docking study against mycobacterial enoyl reductase (InhA) could provide well-clustered solutions to the binding modes and affinity for these molecules as compound 5l showed glide score of -12.275 and glide energy of -54.937 kcal/mol.

Design and Synthesis of Highly Active Antimycobacterial Mutual Esters of 2-(2-Isonicotinoylhydrazineylidene)propanoic Acid

The combination of two active scaffolds into one molecule represents a proven approach in drug design to overcome microbial drug resistance. We designed and synthesized more lipophilic esters of 2-(2-isonicotinoylhydrazineylidene)propanoic acid, obtained from antitubercular drug isoniazid, with various alcohols, phenols and thiols, including several drugs, using carbodiimide-mediated coupling. Nineteen new esters were evaluated as potential antimycobacterial agents against drug-sensitive Mycobacterium tuberculosis (Mtb.) H₃₇Rv, Mycobacterium avium and Mycobacterium kansasii. Selected derivatives were also tested for inhibition of multidrug-resistant (MDR) Mtb., and their mechanism of action was investigated. The esters exhibited high activity against Mtb. (minimum inhibitory concentrations, MIC, from ≤0.125 μM), M. kansasii, M. avium as well as MDR strains (MIC from 0.25, 32 and 8 µM, respectively). The most active mutual derivatives were derived from 4-chloro/phenoxy-phenols, triclosan, quinolin-8-ol, naphthols and terpene alcohols. The experiments identified enoyl-acyl carrier protein reductase (InhA), and thus mycobacterial cell wall biosynthesis, as the main target of the molecules that are activated by KatG, but for some compounds can also be expected adjunctive mechanism(s). Generally, the mutual esters have also avoided cytotoxicity and are promising hits for the discovery of antimycobacterial drugs with improved properties compared to parent isoniazid.

Semisynthetic Derivatives of Selected Amaryllidaceae Alkaloids as a New Class of Antimycobacterial Agents

The search for novel antimycobacterial drugs is a matter of urgency, since tuberculosis is still one of the top ten causes of death from a single infectious agent, killing more than 1.4 million people worldwide each year. Nine Amaryllidaceae alkaloids (AAs) of various structural types have been screened for their antimycobacterial activity. Unfortunately, all were considered inactive, and thus a pilot series of aromatic esters of galanthamine, 3-O-methylpancracine, vittatine and maritidine were synthesized to increase biological activity. The semisynthetic derivatives of AAs were screened for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Ra and two other mycobacterial strains (M. aurum, M. smegmatis) using a modified Microplate Alamar Blue Assay. The most active compounds were also studied for their in vitro hepatotoxicity on the hepatocellular carcinoma cell line HepG2. In general, the derivatization of the original AAs was associated with a significant increase in antimycobacterial activity. Several pilot derivatives were identified as compounds with micromolar MICs against M. tuberculosis H37Ra. Two derivatives of galanthamine, 1i and 1r, were selected for further structure optimalization to increase the selectivity index.

Therapeutic Potential of Curcumin as an Antimycobacterial Agent

Curcumin is the principal curcuminoid obtained from the plant Curcuma longa and has been extensively studied for its biological and chemical properties. Curcumin displays a vast range of pharmacological properties, including antimicrobial, anti-inflammatory, antioxidant, and antitumor activity. Specifically, curcumin has been linked to the improvement of the outcome of tuberculosis. There are many reviews on the pharmacological effects of curcumin; however, reviews of the antitubercular activity are comparatively scarcer. In this review, we attempt to discuss the different aspects of the research on the antitubercular activity of curcumin. These include antimycobacterial activity, modulation of the host immune response, and enhancement of BCG vaccine efficacy. Recent advances in the antimycobacterial activity of curcumin synthetic derivatives, the role of computer aided drug design in identifying curcumin targets, the hepatoprotective role of curcumin, and the dosage and toxicology of curcumin will be discussed. While growing evidence supports the use of curcumin and its derivatives for tuberculosis therapy, further preclinical and clinical investigations are of pivotal importance before recommending the use of curcumin formulations in public health.

Two antibacterial spiro compounds from the roots of Artemisia pallens wall: evidence from molecular docking

Bioassay-guided isolation from acetone extract of the roots of Artemisia pallens Wall yielded two spiro compounds (1 and 2). The structures of these compounds were determined on the basis of spectroscopic techniques such as IR, MS, 1 D and 2 D- NMR. The acetone extract, fractions and the isolated two compounds were investigated for their antibacterial activity against two gram negative (E. coli, P. aeruginosa) and two gram positive (S. aureus, B. subtilis) bacterial strains. Compound (2) showed the best spectra of activity with IC₅₀ and MIC values between 2.48-3.08 and 12.78 - 21.77 µM and Compound (1) with 2.57-3.69 and 38.17 - 80.57 µM, respectively, for the four bacterial strains, whereas inactive against Mycobacterium tuberculosis. Molecular docking study could further help in understanding the various interactions between these compounds and DNA gyrase active site in detail and thereby could provide valuable insight into the mechanism of action.

The first synthesis of podocarflavone A and its analogs and evaluation of their antimycobacterial potential against Mycobacterium tuberculosis with the support of virtual screening

The first synthetic route developed for Podocarflavone A reported from Podocarpus macrophyllus and its analogs in 7 steps. Computational analysis for binding with the pantothenate kinase (3AVO) of Mycobacterium tuberculosis showed their docking score (ds) in the range of -8.9 to -9.3 Kcal/mol. MD simulations delineated the stability of the protein-ligand complexes in the TIP3P model. MMGBSA and MMPBSA values of 8d were -42.46 Kcal/mol and -14.58 Kcal/mol, respectively. Further in-vitro antitubercular screening of compounds 8a, 8d, and 8e against M. tuberculosis H37Ra using XRMA protocol exhibited promising antimycobacterial activity with IC₅₀ values 21.82 µg/mL, 15.55 µg/mL, and 16.56 µg/mL, respectively. Compounds 8a, 8d, and 8e showed antibacterial activity with IC₅₀ values 41.56 µg/mL, 24.72 µg/mL, and 72.45 µg/mL respectively against the Staphylococcus aureus. 8a and 8d showed inhibition with IC₅₀ values 39.6 µg/mL and 27.64 µg/mL, respectively, against Bacillus subtilis. The present study could help in the further development of lead molecules against tuberculosis.

Flavanones from the Twigs and Barks of Artocarpus lakoocha Having Antiplasmodial and Anti-TB Activities

Chromatographic separation of the acetone extracts from the twigs and barks of Artocarpus lakoocha led to the isolation of the one new flavanone, lakoochanone (1), together with eleven known compounds (2-12). Lakoochanone (1) and moracin C (4) exhibited weak antiplasmodial activity against Plasmodium falciparum Dd2 with IC₅₀ values of 36.7 and 33.9 µM, respectively. Moreover, moracin C (4) and sanggenofuran B (5) showed cytotoxic activity against A2780 cell line with the respective IC₅₀ values of 15.0 and 57.1 µM. In addition, cyclocommunin (7) displayed strong antimycobacterial activity against Mycobacterium tuberculosis H37Ra with the minimum inhibitory concentration (MIC) value of 12.3 µM.

Design and Synthesis of Pyrano[3,2-b]indolones Showing Antimycobacterial Activity

Latent Mycobacterium tuberculosis infection presents one of the largest challenges for tuberculosis control and novel antimycobacterial drug development. A series of pyrano[3,2-b]indolone-based compounds was designed and synthesized via an original eight-step scheme. The synthesized compounds were evaluated for their in vitro activity against M. tuberculosis strains H37Rv and streptomycin-starved 18b (SS18b), representing models for replicating and nonreplicating mycobacteria, respectively. Compound 10a exhibited good activity with MIC₉₉ values of 0.3 and 0.4 μg/mL against H37Rv and SS18b, respectively, as well as low toxicity, acceptable intracellular activity, and satisfactory metabolic stability and was selected as the lead compound for further studies. An analysis of 10a-resistant M. bovis mutants disclosed a cross-resistance with pretomanid and altered relative amounts of different forms of cofactor F₄₂₀ in these strains. Complementation experiments showed that F₄₂₀-dependent glucose-6-phosphate dehydrogenase and the synthesis of mature F₄₂₀ were important for 10a activity. Overall these studies revealed 10a to be a prodrug that is activated by an unknown F₄₂₀-dependent enzyme in mycobacteria.

Evaluation of Anti-Mycobacterial Compounds in a Silkworm Infection Model with Mycobacteroides abscessus

Among four mycobacteria, Mycobacterium avium, M. intracellulare, M. bovis BCG and Mycobacteroides (My.) abscessus, we established a silkworm infection assay with My. abscessus. When silkworms (fifth-instar larvae, n = 5) were infected through the hemolymph with My. abscessus (7.5 × 10⁷ CFU/larva) and bred at 37 °C, they all died around 40 h after injection. Under the conditions, clarithromycin and amikacin, clinically used antimicrobial agents, exhibited therapeutic effects in a dose-dependent manner. Furthermore, five kinds of microbial compounds, lariatin A, nosiheptide, ohmyungsamycins A and B, quinomycin and steffimycin, screened in an in vitro assay to observe anti-My. abscessus activity from 400 microbial products were evaluated in this silkworm infection assay. Lariatin A and nosiheptide exhibited therapeutic efficacy. The silkworm infection model with My. abscessus is useful to screen for therapeutically effective anti-My. abscessus antibiotics.

Mutually Isomeric 2- and 4-(3-nitro-1,2,4-triazol-1-yl)pyrimidines Inspired by an Antimycobacterial Screening Hit: Synthesis and Biological Activity against the ESKAPE Panel of Pathogens

Starting from the structure of antimycobacterial screening hit OTB-021 which was devoid of activity against ESKAPE pathogens, we designed, synthesized and tested two mutually isomeric series of novel simplified analogs, 2- and 4-(3-nitro-1,2,4-triazol-1-yl)pyrimidines, bearing various amino side chains. These compounds demonstrated a reverse bioactivity profile being inactive against M. tuberculosis while inhibiting the growth of all ESKAPE pathogens (with variable potency patterns) except for Gram-negative P. aeruginosa. Reduction potentials (E_1/2, V) measured for selected compounds by cyclic voltammetry were tightly grouped in the -1.3--1.1 V range for a reversible single-electron reduction. No apparent correlation between the E_1/2 values and the ESKAPE minimum inhibitory concentrations was established, suggesting possible significance of other factors, besides the compounds' reduction potential, which determine the observed antibacterial activity. Generally, more negative E_1/2 values were displayed by 2-(3-nitro-1,2,4-triazol-1-yl)pyrimidines, which is in line with the frequently observed activity loss on moving the 3-nitro-1,2,4-triazol-1-yl moiety from position 4 to position 2 of the pyrimidine nucleus.

Crystallographic evidence for unintended benzisothiazolinone 1-oxide formation from benzothiazinones through oxidation

X-ray crystallography revealed the unintended formation of benziso­thia­zolinone 1-oxides from 1,3-benzo­thia­zin-4-ones through oxidation instead of the anti­cipated benzo­thia­zinone sulfones, which would be constitutional isomers.

1,3-Benzo­thia­zin-4-ones (BTZs) are a promising new class of drugs with activity against Mycobacterium tuberculosis, which have already reached clinical trials. A product obtained in low yield upon treatment of 8-nitro-2-(piperidin-1-yl)-6-(tri­fluoro­meth­yl)-4H-benzo­thia­zin-4-one with 3-chloro­perbenzoic acid, in ana­logy to a literature report describing the formation of sulfoxide and sulfone derived from BTZ043 [Tiwari et al. (2015 ▸). ACS Med. Chem. Lett.6, 128–133], is a ring-contracted benziso­thia­zolinone (BIT) 1-oxide, namely, 7-nitro-2-(piperi­dine-1-carbon­yl)-5-(tri­fluoro­meth­yl)benzo[d]iso­thia­zol-3(2H)-one 1-oxide, C₁₄H₁₂F₃N₃O₅S, as revealed by X-ray crystallography. Single-crystal X-ray analysis of the oxidation product originally assigned as BTZ043 sulfone provides clear evidence that the structure of the purported BTZ043 sulfone is likewise the corresponding BIT 1-oxide, namely, 2-[(S)-2-methyl-1,4-dioxa-8-aza­spiro­[4.5]decane-8-carbon­yl]-7-nitro-5-(tri­fluoro­meth­yl)benzo[d]iso­thia­zol-3(2H)-one 1-oxide, C₁₇H₁₆F₃N₃O₇S. A possible mechanism for the ring contraction affording the BIT 1-oxides instead of the anti­cipated constitutionally isomeric BTZ sulfones and anti­mycobacterial activities thereof are discussed.

Synthesis of Novel Sulfamethaoxazole 4-Thiazolidinone Hybrids and Their Biological Evaluation

A search for potent antitubercular agents prompted us to design and synthesize sulfamethaoxazole incorporated 4-thiazolidinone hybrids (7a–l) by using a cyclocondensation reaction between 4-amino-N-(5-methylisoxazol-3-yl)benzenesulfonamide (4), aryl aldehyde (5a–l), and mercapto acetic acid (6) resulting in good to excellent yields. All the newly synthesized 4-thiazolidinone derivatives were screened for their in vitro antitubercular activity against M. Bovis BCG and M. tuberculosis H37Ra (MTB) strains. The compounds 7d, 7g, 7i, 7k, and 7l revealed promising antimycobacterial activity against M. Bovis and MTB strains with IC₉₀ values in the range of 0.058–0.22 and 0.43–5.31 µg/mL, respectively. The most active compounds were also evaluated for their cytotoxicity against MCF-7, HCT 116, and A549 cell lines and were found to be non-cytotoxic. Moreover, the synthesized compounds were also analyzed for ADME (absorption, distribution, metabolism, and excretion) properties and showed potential as good oral drug candidates.

Some New Hydrazone Derivatives Bearing the 1,2,4-Triazole Moiety as Potential Antimycobacterial Agents

Objectives

The aim of this study was to synthesize, characterize, and screen some new 1-(4-((2-(4-substitutedphenyl)hydrazono)methyl)phenyl)-1H-1,2,4-triazole derivatives for their antimycobacterial activities.

Materials and Methods

The target compounds (2a-h) were gained by condensation of 4-(1H-1,2,4-triazol-1-yl)benzaldehyde with appropriate phenylhydrazines. Their structures were elucidated by IR, ¹H-NMR, and mass spectrometry. The antimycobacterial activities of the compounds were determined in vitro against Mycobacterium tuberculosis H37Rv.

Results

The biological assay results showed that the methylsulfonyl-substituted derivative 2f displayed the highest antimycobacterial activity in this series.

Conclusion

Although the methylsulfonyl-substituted derivative exhibited significant antimycobacterial activity, none of the synthesized compounds was as effective as isoniazid, rifampin, ethambutol, and ciprofloxacin against M. tuberculosis.

N-Alkyl-2-[4-(trifluoromethyl)benzoyl]hydrazine-1-carboxamides and Their Analogues: Synthesis and Multitarget Biological Activity

Based on the isosterism concept, we have designed and synthesized homologous N-alkyl-2-[4-(trifluoromethyl)benzoyl]hydrazine-1-carboxamides (from C₁ to C₁₈) as potential antimicrobial agents and enzyme inhibitors. They were obtained from 4-(trifluoromethyl)benzohydrazide by three synthetic approaches and characterized by spectral methods. The derivatives were screened for their inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) via Ellman’s method. All the hydrazinecarboxamides revealed a moderate inhibition of both AChE and BuChE, with IC₅₀ values of 27.04–106.75 µM and 58.01–277.48 µM, respectively. Some compounds exhibited lower IC₅₀ for AChE than the clinically used drug rivastigmine. N-Tridecyl/pentadecyl-2-[4-(trifluoromethyl)benzoyl]hydrazine-1-carboxamides were identified as the most potent and selective inhibitors of AChE. For inhibition of BuChE, alkyl chain lengths from C₅ to C₇ are optimal substituents. Based on molecular docking study, the compounds may work as non-covalent inhibitors that are placed in a close proximity to the active site triad. The compounds were evaluated against Mycobacterium tuberculosis H₃₇Rv and nontuberculous mycobacteria (M. avium, M. kansasii). Reflecting these results, we prepared additional analogues of the most active carboxamide (n-hexyl derivative 2f). N-Hexyl-5-[4-(trifluoromethyl)phenyl]-1,3,4-oxadiazol-2-amine (4) exhibited the lowest minimum inhibitory concentrations within this study (MIC ≥ 62.5 µM), however, this activity is mild. All the compounds avoided cytostatic properties on two eukaryotic cell lines (HepG2, MonoMac6).

Phytochemical Investigation, Antioxidant and Antimycobacterial Activities of Schkuhria pinnata (Lam) Thell Extracts Against Mycobacterium smegmatis

The focus of this study was to evaluate the antioxidants and antimycobacterial activities of extracts of Schkuhria pinnata. Serial exhaustive extraction procedure was employed using solvents of varying polarity to obtain the desired extracts. Thin layer chromatography and standard chemical tests were used to analyze phytochemicals constituents. Free radical scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods were used to detect the presence of antioxidant compounds. Antimycobacterial activity was evaluated using microdilution and bioautography assays. A variety of secondary metabolites such as flavonoids, tannins, and alkaloids were detected in the extract. Ethyl acetate and acetone extracts had high antioxidant activity on chromatograms eluted in ethyl acetate/methanol/water while methanol extract at various concentrations had the best scavenging activity. The minimum inhibitory concentration (MIC) values ranged from 0.02 to 2.50 mg/mL. Total phenol content was 55.33 ± 3.51 mg of gallic acid equivalent (GAE)/g and higher when compared with flavonoids (4.00 ± 0.35 mg of quercetin equivalent [QE]/mg) and tannin content (28.00 ± 1.73 mg of GAE/g). The most effective antimycobacterial activity against Mycobacterium smegmatis was observed with the lowest inhibitory concentrations of acetone (0.27 mg/mL), dichloromethane (0.32 mg/mL), and ethyl acetate (0.32 mg/mL) in that order. In massive extraction, hexane and dichloromethane had the greatest inhibitory bands on benzene/ethanol/ammonium hydroxide bioautograms. Antimmycobacterial activity gives promising potential leads of S pinnata extracts to be used in the development of antimycobacterial drugs. The presence of antioxidant and antimycobacterial compounds requires further isolation and purification.

Does the Effectiveness and Mechanical Strength of Kanamycin-Loaded Bone Cement in Musculoskeletal Tuberculosis Compare to Vancomycin-Loaded Bone Cement

BACKGROUND

Antibiotic-loaded bone cement (ALBC) is used to deliver antimycobacterial agents into the focal lesion of musculoskeletal tuberculosis. Although kanamycin is currently used as an antimycobacterial agent for the treatment of multidrug-resistant tuberculosis, there is no information about its suitability in ALBC.

METHODS

An in vitro experiment was conducted with cylindrical shape of 40 g of bone cement with 1, 2, and 3 g of kanamycin. Eluate (1 mL) was extracted from each specimen to measure the level of elution and antimycobacterial activity on days 1, 4, 7, 14, and 30. The quantity of kanamycin in eluates was evaluated by a liquid chromatography-mass spectrometry system, and the antimycobacterial activity of eluates against Mycobacterium tuberculosis H37Rv was calculated by comparing the minimal inhibitory concentration. The ultimate compression strength was conducted using a material testing system machine (Instron 3366; Instron, Norwood, MA) before and after elution.

RESULTS

Eluates from ALBC containing 2 and 3 g of kanamycin had effective antimycobacterial activity for 30 days, whereas eluates from ALBC containing 1 g of kanamycin were partially active until day 30. The pre-eluted compression strength of kanamycin-loaded cement and vancomycin-loaded cement was weaker as they contained a larger amount of antibiotics. There was no statistical difference between the strength of all kanamycin regimens and 1 g of vancomycin in the ultimate compression test. After 30 days of elution, the strength of all kanamycin-loaded cement and vancomycin-loaded cement cylinders was significantly lower than that of initial specimens (P < .05).

CONCLUSION

The antimycobacterial activity of ALBC containing more than 2 g of kanamycin was effective during a 30-day period. The ultimate compression strength of bone cement loaded with 1-3 g of kanamycin was comparable with 1 g of vancomycin while maintaining effective elution until day 30.

The Chemical Composition and Anti-mycobacterial Activities of Trachyspermum copticum and Pelargonium graveolens Essential Oils

BACKGROUND

Microbial resistance to antibiotics and their adverse effects related to these antibiotics are a matter of global public health in the 21th century. The emergence of drug-resistant strains, has gained the interest of the scientists to discover new antimicrobial agents from the essential oil of medicinal plants.

METHODS

Anti-mycobacterial effects of Trachyspermum copticum and Pelargonium graveolens essential oils were determined against multi-drug resistant clinical strains of Mycobacterium tuberculosis, Mycobacterium kansasii, Mycobacterium fortuitum and standard strain of Mycobacterium tuberculosis H37Rv by a Broth micro-dilution method. Pelargonium graveolens plant named Narmada was discovered by Kulkarni R.N et al. (Patent ID, USPP12425P2) and a formulation comprising thymol obtained from Trachyspermum is useful in the treatment of drug-resistant bacterial infections (Patent ID, US6824795B2). The chemical composition of hydro-distilled essential oils was determined by GC and GC-MS.

RESULTS

Minimum Inhibitory Concentration (MIC) values for T. copticum essential oil against tested isolates were ranged from 19.5 µg/mL to 78 µg/mL. The least minimum inhibitory concentration of P. graveolens extract against M. Kansasii and MDR-TB was 78 µg/ml.

CONCLUSION

The results of the present research introduced T. copticum and P. graveolens essential oils as a remarkable natural anti-mycobacterial agent, but more pharmacological studies are required to evaluate their efficacy in animal models.

Sesquiterpenoids from Pilea cavaleriei

One new cis p-coumaroyl copaborneol-type sesquiterpenoid (1), together with its known trans isomer (2) and six other known p-coumaroyl humulane-type sesquiterpenoids (3-8), were isolated from the whole plants of Pilea cavaleriei. Their structures were determined by spectroscopic data. Compounds 1-4 exhibited moderate antimycobacterial activity against Mycobacterium tuberculosis H₃₇Rv.

Bioactivity of Methoxylated and Methylated 1-Hydroxynaphthalene-2-Carboxanilides: Comparative Molecular Surface Analysis

A series of twenty-six methoxylated and methylated N-aryl-1-hydroxynaphthalene- 2-carboxanilides was prepared and characterized as potential anti-invasive agents. The molecular structure of N-(2,5-dimethylphenyl)-1-hydroxynaphthalene-2-carboxamide as a model compound was determined by single-crystal X-ray diffraction. All the analysed compounds were tested against the reference strain Staphylococcus aureus and three clinical isolates of methicillin-resistant S.aureus as well as against Mycobacterium tuberculosis and M. kansasii. In addition, the inhibitory profile of photosynthetic electron transport in spinach (Spinacia oleracea L.) chloroplasts was specified. In vitro cytotoxicity of the most effective compounds was tested on the human monocytic leukaemia THP-1 cell line. The activities of N-(3,5-dimethylphenyl)-, N-(3-fluoro-5-methoxy-phenyl)- and N-(3,5-dimethoxyphenyl)-1-hydroxynaphthalene-2-carbox- amide were comparable with or even better than the commonly used standards ampicillin and isoniazid. All promising compounds did not show any cytotoxic effect at the concentration >30 µM. Moreover, an in silico evaluation of clogP features was performed for the entire set of the carboxamides using a range of software lipophilicity predictors, and cross-comparison with the experimentally determined lipophilicity (log k), in consensus lipophilicity estimation, was conducted as well. Principal component analysis was employed to illustrate noticeable variations with respect to the molecular lipophilicity (theoretical/experimental) and rule-of-five violations. Additionally, ligand-oriented studies for the assessment of the three-dimensional quantitative structure–activity relationship profile were carried out with the comparative molecular surface analysis to determine electron and/or steric factors that potentially contribute to the biological activities of the investigated compounds.

Discovery of Nosiheptide, Griseoviridin, and Etamycin as Potent Anti-Mycobacterial Agents against Mycobacterium avium Complex

Mycobacterium avium complex (MAC) is a serious disease mainly caused by M. avium and M. intracellulare. Although the incidence of MAC infection is increasing worldwide, only a few agents are clinically used, and their therapeutic effects are limited. Therefore, new anti-MAC agents are needed. Approximately 6600 microbial samples were screened for new anti-mycobacterial agents that inhibit the growth of both M. avium and M. intracellulare, and two culture broths derived from marine actinomycete strains OPMA1245 and OPMA1730 had strong activity. Nosiheptide (1) was isolated from the culture broth of OPMA1245, and griseoviridin (2) and etamycin (viridogrisein) (3) were isolated from the culture broth of OPMA1730. They had potent anti-mycobacterial activity against M. avium and M. intracellulare with minimum inhibitory concentrations (MICs) between 0.024 and 1.56 μg/mL. In addition, a combination of 2 and 3 markedly enhanced the anti-mycobacterial activity against both M. avium and M. intracellulare. Furthermore, a combination 2 and 3 had a therapeutic effect comparable to that of ethambutol in a silkworm infection assay with M. smegmatis.

Derivatives of 3-Aminopyrazine-2-carboxamides: Synthesis, Antimicrobial Evaluation, and in Vitro Cytotoxicity

We report the design, synthesis, and in vitro antimicrobial activity of a series of N-substituted 3-aminopyrazine-2-carboxamides with free amino groups in position 3 on the pyrazine ring. Based on various substituents on the carboxamidic moiety, the series is subdivided into benzyl, alkyl, and phenyl derivatives. The three-dimensional structures of the title compounds were predicted using energy minimization and low mode molecular dynamics under AMBER10:EHT forcefield. Compounds were evaluated for antimycobacterial, antibacterial, and antifungal activities in vitro. The most active compound against Mycobacterium tuberculosis H37Rv (Mtb) was 3-amino-N-(2,4-dimethoxyphenyl)pyrazine-2-carboxamide (17, MIC = 12.5 µg/mL, 46 µM). Antimycobacterial activity against Mtb and M. kansasii along with antibacterial activity increased among the alkyl derivatives with increasing the length of carbon side chain. Antibacterial activity was observed for phenyl and alkyl derivatives, but not for benzyl derivatives. Antifungal activity was observed in all structural subtypes, mainly against Trichophyton interdigitale and Candida albicans. The four most active compounds (compounds 10, 16, 17, 20) were evaluated for their in vitro cytotoxicity in HepG2 cancer cell line; only compound 20 was found to exert some level of cytotoxicity. Compounds belonging to the current series were compared to previously published, structurally related compounds in terms of antimicrobial activity to draw structure activity relationships conclusions.

Sulfated Ceria Catalyzed Synthesis of Imidazopyridines and Their Implementation as DNA Minor Groove Binders

The small molecules that bind to DNA minor groove are considered as potential therapeutic agents to fight against many human diseases. They induce cell death by interfering with transcription, replication and progression of cell cycle. Herein, we report the synthesis of imidazopyridine-3-amines using sulfated ceria catalyst by employing Groebkee-Blackburne-Bienayme reaction. We evaluated the possible antiproliferative and antimycobacterial activity against A549 cells and Mycobacterium tuberculosis, respectively. Among the tested compounds, N-tert-butyl-2-(2-butyl-4-chloro-1H-imidazol-5-yl)-5,7-dimethylimidazo[1,2-a]pyridin-3-amine (4g) was identified as cytotoxic heterocycle and antimycobacterial agent. Molecular docking studies of the imidazopyridine derivatives revealed the consistent positioning in the minor groove with a tight shape fit between receptor and ligands. Therefore, we speculate that new imidazopyridines induce their pharmacological effect by targeting the minor groove of DNA.

In vitro inhibition potential of mono-n-octyl phthalate on Mycobacterium tuberculosis H37Ra: Possibility of binding to mycobacterial PknB-An in silico approach

Fatty acids of specific chain lengths have been shown to inhibit the growth of Mycobacterium tuberculosis. In the present study, specific synthetic aromatic derivatives of n-octyl esters were investigated for their property to inhibit the growth of M. tuberculosis H37Ra. Agar well diffusion assay indicated that the crude synthetic derivatives obtained by the esterification of phthalic acid (PA) and n-octanol exhibited antimycobacterial activity. Further, the activity was authenticated with the Miroplate Alamar Blue Assay (MABA). Subsequently, the active component was purified by bioactivity guided chromatographic fractionation. The structure of the synthetic derivative was deduced by UV-Vis, FT-IR, LC-MS, GC-mass spectrometry, and NMR spectroscopy. Molecular docking and molecular dynamic simulation (MDS) were performed with Autodock 4.0 and GROMACS 5.1.2 softwares, respectively. It was found that mono-n-octyl phthalate (MOP) exhibited antimycobacterial activity with a MIC of 20 μg/mL, and not by any other related compounds, including di-n-octyl phthalate, PA, phthalic anhydride, and n-octanol. Binding of MOP with protein kinase B can participate in the binding cavity region, which was previously reported. Subsequently, we authenticate the stability with MDS. This is first report on the inhibition of M. tuberculosis growth by MOP.

Enhancement of the antimycobacterial activity of macrophages by ajoene

Ajoene, a garlic-derived sulfur-containing compound, has broad-spectrum antimicrobial activity. To assess the potential of ajoene for treating tuberculosis (TB), we determined whether it induces the stress response of the endoplasmic reticulum (ER), which plays an important role in TB. We showed that ajoene stimulation induced the production of ER stress sensor molecules and reactive oxygen species (ROS) levels. Ajoene-induced ROS production was dependent on c-Jun N-terminal kinase (JNK) activation. Interestingly, the inhibition of JNK activity and suppression of ROS production reduced ajoene-induced CHOP production in macrophages. Because ER stress activates autophagy, the activation of which suppresses the growth of mycobacteria, we investigated the ajoene-induced production of autophagy-related factors, including LC3-II, P62 and Beclin-1. As expected, ajoene treatment increased the levels of these factors in RAW 264.7 cells. Remarkably, the total amount of Mycobacterium tuberculosis (Mtb) H37Rv was significantly reduced in ajoene-treated RAW 264.7 cells. The treatment of macrophages with ajoene resulted in the activation of JNK, induction of ROS synthesis and accumulation of ROS, possibly leading to the activation of ER stress and autophagy. These results reveal the mechanism of the antimycobacterial effects of ajoene against Mtb H37Rv. Our findings might facilitate the development of novel therapies for patients with TB.

An Update on the Structure of Oxazolidinone Analogs and a Comparison with Linezolid in Terms of In Vitro and Intracellular Efficacy against Clinically Relevant Bacterial Species

Oxazolidinones constitute a novel class of antimicrobials as inhibitors of bacterial ribosomal protein synthesis. In this study, we identified 15 novel oxazolidinone analogs with potent antituberculosis activities. Compounds sy124 and sy125 showed the best activity in vitro (better than that of the linezolid) against various clinically relevant bacterial species, including most Gram-positive bacteria, Mycobacterium spp., and Helicobacter pylori. A cell-based assay indicated that these compounds have a strong ability to kill intracellular pathogens. Our results reveal that the newly identified compounds may be further developed as novel antimicrobial agents.

Antimycobacterial Activities of N-Substituted-Glycinyl 1H-1,2,3-Triazolyl Oxazolidinones and Analytical Method Development and Validation for a Representative Compound

Twelve N-substituted-glycinyl triazolyl oxazolidinone derivatives were screened for antimycobacterial activity against susceptible (Mycobacteriumtuberculosis (Mtb) H37Rv) and resistant (isoniazid (INH)-resistant Mtb (SRI 1369), rifampin (RMP)-resistant Mtb (SRI 1367), and ofloxacin (OFX)-resistant Mtb (SRI 4000)) Mtb strains. Most of the compounds showed moderate to strong antimycobacterial activity against all strains tested, with minimum inhibitory concentration (MIC) value ranges of 0.5-11.5, 0.056-11.6, 0.11-5.8, and 0.03-11.6 μM, and percent inhibition ranges of 41-79%, 51-72%, 50-75%, and 52-71% against Mtb H37Rv, INH-R, RMP-R, and OFX-R M.tuberculosis, respectively. The 3,5-dinitrobenzoyl and 5-nitrofuroyl derivatives demonstrated strong antimycobacterial activities with the N-(5-nitrofuroyl) derivatives (PH-145 and PH-189) being the most potent, with MIC value range of 0.3-0.6 μM against all strains tested. Compounds were not bactericidal, but showed intracellular (macrophage) antimycobacterial activity. A reliable validated analytical method was developed for a representative compound PH-189 using Waters Acquity ultra High-Performance Liquid Chromatography (UHPLC) system with quaternary Solvent Manager (H-Class). A simple extraction method indicated that PH-189 was stable in human plasma after 90 min at 37 °C with more than 90% successfully recovered. Moreover, stress stability studies were performed and degradants were identified by using UHPLC-ESI-QToF under acidic, basic, and oxidative simulated conditions.

Sulfadiazine Salicylaldehyde-Based Schiff Bases: Synthesis, Antimicrobial Activity and Cytotoxicity

The resistance among microbes has brought an urgent need for new drugs. Thus, we synthesized a series of Schiff bases derived from the sulfa drug sulfadiazine and various salicylaldehydes. The resulting 4-[(2-hydroxybenzylidene)amino]-N-(pyrimidin-2-yl)benzene-sulfonamides were characterized and evaluated against Gram-positive and Gram-negative bacteria, yeasts, moulds, Mycobacterium tuberculosis, nontuberculous mycobacteria (M. kansasii, M. avium) and their cytotoxicity was determined. Among bacteria, the genus Staphylococcus, including methicillin-resistant S. aureus, showed the highest susceptibility, with minimum inhibitory concentration values from 7.81 µM. The growth of Candida sp. and Trichophyton interdigitale was inhibited at concentrations starting from 1.95 µM. 4-[(2,5-Dihydroxybenzylidene)amino]-N-(pyrimidin-2-yl)-benzenesulfonamide was identified as the most selective Schiff base for these strains with no apparent cytotoxicity and a selectivity index higher than 16. With respect to M. tuberculosis and M. kansasii that were inhibited within the range of 8 to 250 µM, unsubstituted 4-[(2-hydroxy-benzylidene)amino]-N-(pyrimidin-2-yl)benzenesulfonamide meets the selectivity requirement. In general, dihalogenation of the salicylic moiety improved the antibacterial and antifungal activity but also increased the cytotoxicity, especially with an increasing atomic mass. Some derivatives offer more advantageous properties than the parent sulfadiazine, thus constituting promising hits for further antimicrobial drug development.

Design, Synthesis, Antimycobacterial Evaluation, and In Silico Studies of 3-(Phenylcarbamoyl)-pyrazine-2-carboxylic Acids

Pyrazinamide, the first-line antitubercular drug, has been regarded the basic component of tuberculosis treatment for over sixty years. Researchers have investigated its effect on Mycobacterium tuberculosis for this long time, and as a result, new potential targets of pyrazinamide or its active form, pyrazinoic acid, have been found. We have designed and prepared 3-(phenyl-carbamoyl)pyrazine-2-carboxylic acids as more lipophilic derivatives of pyrazinoic acid. We also prepared methyl and propyl derivatives as prodrugs with further increased lipophilicity. Antimycobacterial, antibacterial and antifungal growth inhibiting activity was investigated in all prepared compounds. 3-[(4-Nitrophenyl)carbamoyl]pyrazine-2-carboxylic acid (16) exerted high antimycobacterial activity against Mycobacterium tuberculosis H37Rv with MIC = 1.56 μg·mL⁻¹ (5 μM). Propyl 3-{[4-(trifluoromethyl)phenyl]carbamoyl}pyrazine-2-carboxylate (18a) showed also high antimycobacterial activity against Mycobacterium tuberculosis H37Rv with MIC = 3.13 μg·mL⁻¹. In vitro cytotoxicity of the active compounds was investigated and no significant cytotoxic effect was observed. Based to structural similarity to known inhibitors of decaprenylphosphoryl-β-d-ribose oxidase, DprE1, we performed molecular docking of the prepared acids to DprE1. These in silico experiments indicate that modification of the linker connecting aromatic parts of molecule does not have any negative influence on the binding.

Antimycobacterial, docking and molecular dynamic studies of pentacyclic triterpenes from Buddleja saligna leaves

Buddleja saligna (family Buddlejaceae) is a medicinal plant endemic to South Africa. Two isomeric pentacyclic triterpenes, oleanolic acid and ursolic acid, were isolated from the leaves of B. saligna using silica gel column chromatography. Compounds oleanolic acid and ursolic acid were subjected to derivatization with acetic anhydride in the presence of pyridine to obtain oleanolic acid-3-acetate and ursolic acid-3-acetate, respectively. The structures of these compounds were fully characterized by detailed nuclear magnetic resonance (NMR) investigations, which included 1H and 13C NMR. Molecular docking studies predicted the free binding energy of the four triterpenes inside the steroid binding pocket of Mycobacterium tuberculosis fadA5 thiolase compared to a reported inhibitor. Thus, their ability to inhibit the growth of M. tuberculosis was predicted and was confirmed to possess significant antimycobacterial activity when tested against Mycobacterium smegmatis, M. tuberculosis H37Rv (ATCC 25177), clinical isolates of multi-drug-resistant M. tuberculosis (MDR-TB) and extensively drug-resistant M. tuberculosis (XDR-TB) using the Micro Alamar Blue Assay. Ursolic acid was isolated from this plant for the first time.

Discovery of Indeno[1,2-c]quinoline Derivatives as Potent Dual Antituberculosis and Anti-Inflammatory Agents

A series of indeno[1,2-c]quinoline derivatives were designed, synthesized and evaluated for their anti-tuberculosis (anti-TB) and anti-inflammatory activities. The minimum inhibitory concentration (MIC) of the newly synthesized compound was tested against Mycobacterium tuberculosis H₃₇R_V. Among the tested compounds, (E)-N′-[6-(4-hydroxypiperidin-1-yl)-11H-indeno[1,2-c]quinolin-11-ylidene]isonicotino-hydrazide (12), exhibited significant activities against the growth of M. tuberculosis (MIC values of 0.96 μg/mL) with a potency approximately equal to that of isoniazid (INH), an anti-TB drug. Important structure features were analyzed by quantitative structure–activity relationship (QSAR) analysis to give better insights into the structure determinants for predicting the anti-TB activity. The anti-inflammatory activity was induced by superoxide anion generation and neutrophil elastase (NE) release using the formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLF)-activated human neutrophils method. Results indicated that compound 12 demonstrated a potent dual inhibitory effect on NE release and superoxide anion generation with IC₅₀ values of 1.76 and 1.72 μM, respectively. Our results indicated that compound 12 is a potential lead compound for the discovery of dual anti-TB and anti-inflammatory drug candidates. In addition, 6-[3-(hydroxymethyl)piperidin-1-yl]-9-methoxy-11H-indeno[1,2-c]quinolin-11-one (4g) showed a potent dual inhibitory effect on NE release and superoxide anion generation with IC₅₀ values of 0.46 and 0.68 μM, respectively, and is a potential lead compound for the discovery of anti-inflammatory drug candidates.

Novel Sulfamethoxazole Ureas and Oxalamide as Potential Antimycobacterial Agents

Infections caused by Mycobacterium tuberculosis (Mtb.) and nontuberculous mycobacteria (NTM) are considered to be a global health problem; current therapeutic options are limited. Sulfonamides have exhibited a wide range of biological activities including those against mycobacteria. Based on the activity of 4-(3-heptylureido)-N-(5-methylisoxazol-3-yl)benzenesulfonamide against NTM, we designed a series of homologous sulfamethoxazole-based n-alkyl ureas (C₁–C₁₂), as well as several related ureas and an oxalamide. Fifteen ureas and one oxalamide were synthesized by five synthetic procedures and characterized. They were screened for their activity against Mtb. and three NTM strains (M. avium, M. kansasii). All of them share antimycobacterial properties with minimum inhibitory concentration (MIC) values starting from 2 µM. The highest activity showed 4,4′-[carbonylbis(azanediyl)]bis[N-(5-methylisoxazol-3-yl)benzenesulfonamide] with MIC of 2–62.5 µM (i.e., 1.07–33.28 µg/mL). Among n-alkyl ureas, methyl group is optimal for the inhibition of both Mtb. and NTM. Generally, longer alkyls led to increased MIC values, heptyl being an exception for NTM. Some of the novel derivatives are superior to parent sulfamethoxazole. Several urea and oxalamide derivatives are promising antimycobacterial agents with low micromolar MIC values.

3-Substituted N-Benzylpyrazine-2-carboxamide Derivatives: Synthesis, Antimycobacterial and Antibacterial Evaluation

A series of substituted N-benzyl-3-chloropyrazine-2-carboxamides were prepared as positional isomers of 5-chloro and 6-chloro derivatives, prepared previously. During the aminolysis of the acyl chloride, the simultaneous substitution of chlorine with benzylamino moiety gave rise to N-benzyl-3-(benzylamino)pyrazine-2-carboxamides as side products, in some cases. Although not initially planned, the reaction conditions were modified to populate this double substituted series. The final compounds were tested against four mycobacterial strains. N-(2-methylbenzyl)-3-((2-methylbenzyl)amino)pyrazine-2-carboxamide (1a) and N-(3,4-dichlorobenzyl)-3-((3,4-dichlorobenzyl)amino)pyrazine-2-carboxamide (9a) proved to be the most effective against Mycobacterium tuberculosis H37Rv, with MIC = 12.5 μg·mL^-1. Compounds were screened for antibacterial activity. The most active compound was 3-chloro-N-(2-chlorobenzyl)pyrazine-2-carboxamide (5) against Staphylococcus aureus with MIC = 7.81 μM, and Staphylococcus epidermidis with MIC = 15.62 μM. HepG2 in vitro cytotoxicity was evaluated for the most active compounds; however, no significant toxicity was detected. Compound 9a was docked to several conformations of the enoyl-ACP-reductase of Mycobacterium tuberculosis. In some cases, it was capable of H-bond interactions, typical for most of the known inhibitors.

In Vitro-In Vivo Evaluation of Novel Co-spray Dried Rifampicin Phospholipid Lipospheres for Oral Delivery

The objective of this study comprises of developing novel co-spray dried rifampicin phospholipid lipospheres (SDRPL) to investigate its influence on rifampicin solubility and oral bioavailability. Solid-state techniques were employed to characterize the liposphere formulation. SDRPL solubility was determined in distilled water. BACTEC 460TB System was employed to evaluate SDRPL antimycobacterial activity. The oral bioavailability of the lipospheres was evaluated in Sprague Dawley rats. Lipospheres exhibited amorphous, smooth spherical morphology with a significant increase (p < 0.001) in solubility of SDRPL (2:1), 350.9 ± 23 versus 105.1 ± 12 μg/ml and SDRPL (1:1) 306.4 ± 20 versus 105.1 ± 12 μg/ml in comparison to rifampicin (RMP). SDRPL exhibited enhanced activity against Mycobacterium tuberculosis, H37Rv strain, with over twofolds less minimum inhibitory concentration (MIC) than the free drug. Lipospheres exhibited higher peak plasma concentration (109.92 ± 25 versus 54.31 ± 18 μg/ml), faster T _max (two versus four hours), and enhanced area under the curve (AUC_0-∞) (406.92 ± 18 versus 147.72 ± 15 μg h/L) in comparison to pure RMP. Thus, SDRPL represents a promising carrier system exhibiting enhanced antimycobacterial activity and oral bioavailability of rifampicin.

Cytotoxic Labdane Diterpenes from Hedychium ellipticum Buch.-Ham. ex Sm

In order to reveal the constituents and their biological activities, we carried out a phytochemical study on Hedychium ellipticum Buch.-Ham. ex Sm. (Zingiberaceae). Ten labdane diterpenoids (1–10) were isolated from the rhizomes of H. ellipticum for the first time. Their structures were identified on the basis of spectroscopic analyses including two-dimensional NMR and comparison with literature data. All of these compounds were evaluated for their antimycobacterial activity against Mycobacterium tuberculosis and cytotoxicity against KB, MCF7, NCI-H187 and Vero cells. The result showed that compounds 1 and 7 exhibited moderate activity against Mycobacterium tuberculosis and compounds 4, 6 and 7 displayed remarkable cytotoxic activity. This is the first report on the presence of all compounds in H. ellipticum and the first time that their structure activity relationship has been discussed.

Triazolophthalazines: Easily Accessible Compounds with Potent Antitubercular Activity

Tuberculosis (TB) remains one of the major causes of death worldwide, in particular because of the emergence of multidrug-resistant TB. Herein we explored the potential of an alternative class of molecules as anti-TB agents. Thus, a series of novel 3-substituted triazolophthalazines was quickly and easily prepared from commercial hydralazine hydrochloride as starting material and were further evaluated for their antimycobacterial activities and cytotoxicities. Four of the synthesized compounds were found to effectively inhibit the Mycobacterium tuberculosis (M.tb) H37 Rv strain with minimum inhibitory concentration (MIC) values <10 μg mL(-1) , whereas no compounds displayed cytotoxicity against HCT116 human cell lines (IC50 >100 μm). More remarkably, the most potent compounds proved to be active to a similar extent against various multidrug-resistant M.tb strains, thus uncovering a mode of action distinct from that of standard antitubercular agents. Overall, their ease of preparation, combined with their attractive antimycobacterial activities, make such triazolophthalazine-based derivatives promising leads for further development.

Design, Synthesis and Antimycobacterial Activity of Novel Imidazo[1,2-a]pyridine Amide-Cinnamamide Hybrids

We report herein the design and synthesis of a series of novel imidazo[1,2-a]pyridine amide-cinnamamide hybrids linked via an alkyl carbon chain. All 38 new hybrids were evaluated for their antimycobacterial activity against M. tuberculosis (MTB) H37Rv ATCC 27294 using the microplate Alamar Blue assay (MABA). Although the hybrids are less active than the two reference compounds, the promising activity (MICs: 4 μg/mL) of 2,6-dimethylimidazo[1,2-a]pyridine amide-cinnamamide hybrids 11e and 11k could be a good starting point to further find new lead compounds against multi-drug-resistant tuberculosis.

Design, Synthesis, and Antimycobacterial Activity of Novel Theophylline-7-Acetic Acid Derivatives With Amino Acid Moieties

The theophylline-7-acetic acid (7-TAA) scaffold is a promising novel lead compound for antimycobacterial activity. Here, we derive a model for antitubercular activity prediction based on 14 7-TAA derivatives with amino acid moieties and their methyl esters. The model is applied to a combinatorial library, consisting of 40 amino acid and methyl ester derivatives of 7-TAA. The best three predicted compounds are synthesized and tested against Mycobacterium tuberculosis H37Rv. All of them are stable, non-toxic against human cells and show antimycobacterial activity in the nanomolar range being 60 times more active than ethambutol.

New pimarane diterpenes and other antimycobacterial metabolites from Anisochilus verticillatus

Phytochemical investigation of the acetone extract of the aerial parts of Anisochilus verticillatus afforded a new 8,9-secopimarane diterpene (1), two new isopimarane diterpenes (2, 3) and the known ursolic acid (4), α-amyrin (5), β-amyrin (6), stigmast-5-en-3-one (7) and hydroxychavicol (8). Structures of the new compounds were elucidated with the help of 1D and 2D nuclear magnetic resonance spectroscopic data, and single crystal X-ray crystallography of compound 3. Compounds 2 and 8 inhibited Mycobacterium tuberculosis H37Ra with an IC50 of 11.3 (IC90 of 20.0 μg/mL) and 12.5 μg/mL, respectively. Correspondingly, molecular docking studies with Extra Precision Glide revealed a correlation between score and biological activity for these compounds to describe the molecular basis for the most significant SAR results.

Synthesis and Biological Evaluation of N-Alkyl-3-(alkylamino)-pyrazine-2-carboxamides

A series of N-alkyl-3-(alkylamino)pyrazine-2-carboxamides and their N-alkyl-3-chloropyrazine-2-carboxamide precursors were prepared. All compounds were characterized by analytical methods and tested for antimicrobial and antiviral activity. The antimycobacterial MIC values against Mycobacterium tuberculosis H37Rv of the most effective compounds, 3-(hexylamino)-, 3-(heptylamino)- and 3-(octylamino)-N-methyl-pyrazine-2-carboxamides 14‒16, was 25 μg/mL. The compounds inhibited photosystem 2 photosynthetic electron transport (PET) in spinach chloroplasts. This activity was strongly connected with the lipophilicity of the compounds. For effective PET inhibition longer alkyl chains in the 3-(alkylamino) substituent in the N-alkyl-3-(alkylamino)pyrazine-2-carboxamide molecule were more favourable than two shorter alkyl chains.