Isolation and Characterization of Anti-Mycobacterial Natural Products from a Petrosia sp. Marine Sponge.

Tuberculosis (TB) is a dreadful infectious disease and a leading cause of mortality and morbidity worldwide, second in 2020 only to severe acute respiratory syndrome 2 (SARS-Cov-2). With limited therapeutic options available and a rise in multidrug-resistant tuberculosis cases, it is critical to develop antibiotic drugs that display novel mechanisms of action. Bioactivity-guided fractionation employing an Alamar blue assay for Mycobacterium tuberculosis strain H37Rv led to the isolation of duryne (13) from a marine sponge Petrosia sp. sampled in the Solomon Islands. Additionally, five new strongylophorine meroditerpene analogues (1-5) along with six known strongylophorines (6-12) were isolated from the bioactive fraction and characterized using MS and NMR spectroscopy, although only 13 exhibited antitubercular activity.

New Terpenoids from the Corticioid Fungus Punctularia atropurpurascens and their Antimycobacterial Evaluation.

Chemical investigation of Punctularia atropurpurascens strain HM1 (Punctulariaceae), a corticioid isolated from a decorticated piece of Quercus bark collected in Bosque de Tlalpan, Mexico City, led to the isolation of a new drimane, 1-α-hydroxy-isodrimenine (1: ) and a new tetrahydroxy kauranol, 16-hydroxy-phlebia-nor-kauranol (2: ), together with the known N-phenylacetamide (3: ). Structures of all compounds were elucidated by spectroscopic and spectrometric methods, and the absolute configuration of 1: and 2: was confirmed via single-crystal X-ray crystallography. The isolated compounds showed modest antimycobacterial activity.

Chemical Diversity and Antimicrobial Potential of Cultivable Fungi from Deep-Sea Sediments of the Gulf of Mexico.

A collection of 29 cultivable fungal strains isolated from deep-sea sediments of the Gulf of Mexico were cultivated under the "one strain, many compounds" approach to explore their chemical diversity and antimicrobial potential. From the 87 extracts tested, over 50% showed antimicrobial activity, and the most active ones were those from cultures grown at 4 °C in darkness for 60 days (resembling deep-sea temperature). PCA analysis of the LC-MS data of all the extracts confirmed that culture temperature is the primary factor in the variation of the 4462 metabolite features, accounting for 21.3% of the variation. The bioactivity-guided and conventional chemical studies of selected fungal strains allowed the identification of several active and specialized metabolites. Finally, metabolomics analysis by GNPS molecular networking and manual dereplication revealed the biosynthetic potential of these species to produce interesting chemistry. This work uncovers the chemical and biological study of marine-derived fungal strains from deep-sea sediments of the Gulf of Mexico.

Synthesis and antimicrobial activities of N6-hydroxyagelasine analogs and revision of the structure of ageloximes.

(+)-N6-Hydroxyagelasine D, the enantiomer of the proposed structure of (-)-ageloxime D, as well as N6-hydroxyagelasine analogs were synthesized by selective N-7 alkylation of N6-[tert-butyl(dimethyl)silyloxy]-9-methyl-9H-purin-6-amine in order to install the terpenoid side chain, followed by fluoride mediated removal of the TBDMS-protecting group. N6-Hydroxyagelasine D and the analog carrying a geranylgeranyl side chain displayed profound antimicrobial activities against several pathogenic bacteria and protozoa and inhibited bacterial biofilm formation. However these compounds were also toxic towards mammalian fibroblast cells (MRC-5). The spectral data of N6-hydroxyagelasine D did not match those reported for ageloxime D before. Hence, a revised structure of ageloxime D was proposed. Basic hydrolysis of agelasine D gave (+)-N-[4-amino-6-(methylamino)pyrimidin-5-yl]-N-copalylformamide, a compound with spectral data in full agreement with those reported for (-)-ageloxime D.

Synthesis and Activity against Mycobacterium tuberculosis of Olivacine and Oxygenated Derivatives.

The tetracyclic pyrido[4,3-b]carbazole olivacine and four of its oxygenated derivatives have been synthesized by a late-stage palladium-catalyzed Heck-type cyclization of the pyrrole ring as a key step. In a test for the inhibition of the growth of Mycobacterium tuberculosis, 9-methoxyolivacine showed the most significant inhibitory activity against Mycobacterium tuberculosis, with an MIC90 value of 1.5 µM.

Anti-Mycobacterium tuberculosis Activity of Esters of Quinoxaline 1,4-Di-N-Oxide.

Tuberculosis continues to be a public health problem in the world, and drug resistance has been a major obstacle in its treatment. Quinoxaline 1,4-di-N-oxide has been proposed as a scaffold to design new drugs to combat this disease. To examine the efficacy of this compound, this study evaluates methyl, ethyl, isopropyl, and n-propyl esters of quinoxaline 1,4-di-N-oxide derivatives in vitro against Mycobacterium tuberculosis (pansusceptible and monoresistant strains). Additionally, the inhibitory effect of esters of quinoxaline 1,4-di-N-oxide on M. tuberculosis gyrase supercoiling was examined, and a stability analysis by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS) was also carried out. Results showed that eight compounds (T-007, T-018, T-011, T-069, T-070, T-072, T-085 and T-088) had an activity similar to that of the reference drug isoniazid (minimum inhibitory concentration (MIC) = 0.12 µg/mL) with an effect on nonreplicative cells and drug monoresistant strains. Structural activity relationship analysis showed that the steric effect of an ester group at 7-position is key to enhancing its biological effects. Additionally, T-069 showed a high stability after 24 h in human plasma at 37 °C.

6-Nitro-2,3-dihydroimidazo[2,1-b][1,3]thiazoles: Facile synthesis and comparative appraisal against tuberculosis and neglected tropical diseases.

As part of a quest for backups to the antitubercular drug pretomanid (PA-824), we investigated the unexplored 6-nitro-2,3-dihydroimidazo[2,1-b][1,3]-thiazoles and related -oxazoles. The nitroimidazothiazoles were prepared in high yield from 2-bromo-4-nitroimidazole via heating with substituted thiiranes and diisopropylethylamine. Equivalent examples of these two structural classes provided broadly comparable MICs, with 2-methyl substitution and extended aryloxymethyl side chains preferred; albeit, S-oxidised thiazoles were ineffective for tuberculosis. Favourable microsomal stability data for a biaryl thiazole (45) led to its assessment in an acute Mycobacterium tuberculosis mouse model, alongside the corresponding oxazole (48), but the latter proved to be more efficacious. In vitro screening against kinetoplastid diseases revealed that nitroimidazothiazoles were inactive versus leishmaniasis but showed interesting activity, superior to that of the nitroimidazooxazoles, against Chagas disease. Overall, "thio-delamanid" (49) is regarded as the best lead.

Anti-tuberculosis activity and structure-activity relationships of oxygenated tricyclic carbazole alkaloids and synthetic derivatives.

A series of 49 oxygenated tricyclic carbazole derivatives has been tested for inhibition of the growth of Mycobacterium tuberculosis and a mammalian cell line (vero cells). From this series, twelve carbazoles showed a significant anti-TB activity. The four most active compounds were the naturally occurring carbazole alkaloids clauszoline-M (45), murrayaline-C (41), carbalexin-C (27), and the synthetic carbazole derivative 22 with MIC90 values ranging from 1.5 to 3.7µM. The active compounds were virtually nontoxic for the mammalian cell line in the concentration range up to 50µM.

Discovery of new leads against Mycobacterium tuberculosis using scaffold hopping and shape based similarity.

BM212 [1,5-diaryl-2-methyl-3-(4-methylpiperazin-1-yl)-methyl-pyrrole] is a pyrrole derivative with strong inhibitory activity against drug resistant Mycobacterium tuberculosis and mycobacteria residing in macrophages. However, it was not pursued because of its poor pharmacokinetics and toxicity profile. Our goal was to design and synthesize new antimycobacterial BM212 analogs with lower toxicity and better pharmacokinetic profile. Using the scaffold hopping approach, three structurally diverse heterocycles - 2,3-disubstituted imidazopyridines, 2,3-disubstituted benzimidazoles and 1,2,4-trisubstituted imidazoles emerged as promising antitubercular agents. All compounds were synthesized through easy and convenient methods and their structures confirmed by IR, 1H NMR, 13C NMR and MS. In-vitro cytotoxicity studies on normal kidney monkey cell lines and HepG2 cell lines, as well as metabolic stability studies on rat liver microsomes for some of the most active compounds, established that these compounds have negligible cytotoxicity and are metabolically stable. Interestingly the benzimidazole compound (4a) is as potent as the parent molecule BM212 (MIC 2.3µg/ml vs 0.7-1.5µg/ml), but is devoid of the toxicity against HepG2 cell lines (IC50 203.10µM vs 7.8µM).

Discovery of Novel Oral Protein Synthesis Inhibitors of Mycobacterium tuberculosis That Target Leucyl-tRNA Synthetase.

The recent development and spread of extensively drug-resistant and totally drug-resistant resistant (TDR) strains of Mycobacterium tuberculosis highlight the need for new antitubercular drugs. Protein synthesis inhibitors have played an important role in the treatment of tuberculosis (TB) starting with the inclusion of streptomycin in the first combination therapies. Although parenteral aminoglycosides are a key component of therapy for multidrug-resistant TB, the oxazolidinone linezolid is the only orally available protein synthesis inhibitor that is effective against TB. Here, we show that small-molecule inhibitors of aminoacyl-tRNA synthetases (AARSs), which are known to be excellent antibacterial protein synthesis targets, are orally bioavailable and effective against M. tuberculosis in TB mouse infection models. We applied the oxaborole tRNA-trapping (OBORT) mechanism, which was first developed to target fungal cytoplasmic leucyl-tRNA synthetase (LeuRS), to M. tuberculosis LeuRS. X-ray crystallography was used to guide the design of LeuRS inhibitors that have good biochemical potency and excellent whole-cell activity against M. tuberculosis Importantly, their good oral bioavailability translates into in vivo efficacy in both the acute and chronic mouse models of TB with potency comparable to that of the frontline drug isoniazid.

Biarylmethoxy 2-nitroimidazooxazine antituberculosis agents: Effects of proximal ring substitution and linker reversal on metabolism and efficacy.

Certain biaryl analogues of antitubercular drug PA-824 displayed enhanced in vivo efficacies yet retained some susceptibility towards oxidative metabolism; therefore, two new strategies were explored to address this. Ortho-substitution of the proximal aryl ring with larger electron-withdrawing substituents maintained or improved compound stability but reduced aerobic potency; however, fluoro and cyano were well tolerated. In vivo, only 2'- or 3'-fluoro mono-substitution preserved high efficacy against acute infection, although one example was twofold more effective than delamanid against chronic infection. Reversal of the 6-oxymethylene linkage also permitted high potency and improved stability towards human liver microsomes, albeit, in vivo results were inferior. These novel findings provide further insight into the preferred structural features for lead candidates in this important drug class.

A novel indigoid anti-tuberculosis agent.

The structure of a novel indigoid component was characterized by X-ray crystallography. This compound exhibited excellent anti-tuberculosis activity against Mycobacterium tuberculosis H37Rv in whole cell culture showing a submicromolar minimum inhibitory concentration (MIC). A synthesis of this molecule was designed and carried out to produce sufficient material for further testing. The in vitro profile, structure, and first synthesis of this indigoid component is reported.

Synthesis of 3-(3-aryl-pyrrolidin-1-yl)-5-aryl-1,2,4-triazines that have antibacterial activity and also inhibit inorganic pyrophosphatase.

Inorganic pyrophosphatases are potential targets for the development of novel antibacterial agents. A pyrophosphatase-coupled high-throughput screening assay intended to detect o-succinyl benzoic acid coenzyme A (OSB CoA) synthetase inhibitors led to the unexpected discovery of a new series of novel inorganic pyrophosphatase inhibitors. Lead optimization studies resulted in a series of 3-(3-aryl-pyrrolidin-1-yl)-5-aryl-1,2,4-triazine derivatives that were prepared by an efficient synthetic pathway. One of the tetracyclic triazine analogues 22h displayed promising antibiotic activity against a wide variety of drug-resistant Staphylococcus aureus strains, as well as activity versus Mycobacterium tuberculosis and Bacillus anthracis, at a concentration that was not cytotoxic to mammalian cells.

Airborne antituberculosis activity of Eucalyptus citriodora essential oil.

The rapid emergence of multi- and extensively drug-resistant tuberculosis (MDR/XDR-TB) has created a pressing public health problem, which mostly affects regions with HIV/AIDS prevalence and represents a new constraint in the already challenging disease management of tuberculosis (TB). The present work responds to the need to reduce the number of contagious MDR/XRD-TB patients, protect their immediate environment, and interrupt the rapid spread by laying the groundwork for an inhalation therapy based on anti-TB-active constituents of the essential oil (EO) of Eucalyptus citriodora. In order to address the metabolomic complexity of EO constituents and active principles in botanicals, this study applied biochemometrics, a 3-D analytical approach that involves high-resolution CCC fractionation, GC-MS analysis, bioactivity measurements, and chemometric analysis. Thus, 32 airborne anti-TB-active compounds were identified in E. citriodora EO: the monoterpenes citronellol (1), linalool (3), isopulegol (5), and α-terpineol (7) and the sesquiterpenoids spathulenol (11), ß-eudesmol (23), and τ-cadinol (25). The impact of the interaction of multiple components in EOs was studied using various artificial mixtures (AMxs) of the active monoterpenes 1, 2, and 5 and the inactive eucalyptol (33). Both neat 1 and the AMx containing 1, 2, and 33 showed airborne TB inhibition of >90%, while the major E. citriodora EO component, 2, was only weakly active, at 18% inhibition.

A novel combinatorial biocatalytic approach for producing antibacterial compounds effective against Mycobacterium tuberculosis (TB).

Two bacterial hosts expressing cloned aromatic oxygenases were used to catalyze the oxidation and polymerization of indole and related substrates, creating mixtures of indigoid compounds comprised of novel dimers and trimers. Crude extracts and purified compounds were tested for their ability to inhibit the growth of Gram-positive organisms, in general, and Mycobacterium tuberculosis (TB), in particular. Of the 74 compounds tested against M. tuberculosis, ~66 % had minimum inhibitory concentrations (MIC) of 5 µg/ml or less. The most effective antibiotic found was designated SAB-P1, a heterodimer of indole and anthranil, which had a MIC of 0.16 µg/ml, and did not inhibit kidney cells (IC(50)) at concentrations of >8 µg/ml. Combinatorial biocatalysis was used to create a series of halogenated derivatives of SAB-P1 with a wider therapeutic window. None of the derivatives had MIC values that were superior to SAB-P1, but some had a wider therapeutic window because of decreased kidney cell toxicity. Generally, the indigoid dimers that were effective against TB appeared to be specific for TB. Some of the trimers generated, however, had a broader spectrum of activity inhibiting not only TB (MIC = 1.1 µg/ml) but also the growth of Mycobacterium smegmatis MC2 155, Bacillus cereus, Enterococcus faecalis, Staphylococcus epidermidis, Bacillus subtilis 168, and Clostridium acetobutylicum. The structure of two of the novel dimers (SAB-C4 and SAB-P1) and a trimer (SAB-R1) were solved using X-ray crystallography.

Evaluation of gyrase B as a drug target in Mycobacterium tuberculosis.

OBJECTIVES: New classes of drugs are needed to treat tuberculosis (TB) in order to combat the emergence of resistance to existing agents and shorten the duration of therapy. Targeting DNA gyrase is a clinically validated therapeutic approach using fluoroquinolone antibiotics to target the gyrase subunit A (GyrA) of the heterotetramer. Increasing resistance to fluoroquinolones has driven interest in targeting the gyrase subunit B (GyrB), which has not been targeted for TB. The biological activities of two potent small-molecule inhibitors of GyrB have been characterized to validate its targeting as a therapeutic strategy for treating TB. MATERIALS AND METHODS: Novobiocin and aminobenzimidazole 1 (AB-1) were tested for their activity against Mycobacterium tuberculosis (Mtb) H37Rv and other mycobacteria. AB-1 and novobiocin were also evaluated for their interaction with rifampicin and isoniazid as well as their potential for cytotoxicity. Finally, AB-1 was tested for in vivo efficacy in a murine model of TB. RESULTS: Novobiocin and AB-1 have both been shown to be active against Mtb with MIC values of 4 and 1 mg/L, respectively. Only AB-1 exhibited time-dependent bactericidal activity against drug-susceptible and drug-resistant mycobacteria, including a fluoroquinolone-resistant strain. AB-1 had potent activity in the low oxygen recovery assay model for non-replicating persistent Mtb. Additionally, AB-1 has no interaction with isoniazid and rifampicin, and has no cross-resistance with fluoroquinolones. In a murine model of TB, AB-1 significantly reduced lung cfu counts in a dose-dependent manner. CONCLUSIONS: Aminobenzimidazole inhibitors of GyrB exhibit many of the characteristics required for their consideration as a potential front-line antimycobacterial therapeutic.

Structural requirements for the antitubercular quaternized triflupromazine pharmacophore.

Quaternized triflupromazine derivatives (QTDs) must possess benzyl groups attached to the quaternary nitrogen in order to have significant antitubercular potency. Replacing the quaternary amine with a triazole abolishes antitubercular activity. A modest halogen substitution effect exists, with the 4-bromophenyl QTD 3 having the best selectivity index (>21). All N-benzyl QTDs 1-4 similarly inhibit non-replicating, persistent Mycobacterium tuberculosis with MIC<8 µM, and compounds 1-3 were all nontoxic to mammalian cells in vitro (IC(50)>128 µM).

Construction and functionalization of fused pyridine ring leading to novel compounds as potential antitubercular agents.

A series of fused and functionalized pyridine derivatives were designed, synthesized and tested for their potential antitubercular properties. All these novel compounds were prepared by using multistep methods involving the construction of pyridine ring as a key synthetic step. Some of these compounds were found to be interesting when tested for their antitubercular properties in vitro and one of them appeared as an attractive and potential antitubercular agent.

Insights into the Chemical Diversity of Selected Fungi from the Tza Itzá Cenote of the Yucatan Peninsula.

Cenotes are habitats with unique physical, chemical, and biological features. Unexplored microorganisms from these sinkholes represent a potential source of bioactive molecules. Thus, a series of cultivable fungi (Aspergillus spp. NCA257, NCA264, and NCA276, Stachybotrys sp. NCA252, and Cladosporium sp. NCA273) isolated from the cenote Tza Itzá were subjected to chemical, coculture, and metabolomic analyses. Nineteen compounds were obtained and tested for their antimicrobial potential against ESKAPE pathogens, Mycobacterium tuberculosis, and nontuberculous mycobacteria. In particular, phenylspirodrimanes from Stachybotrys sp. NCA252 showed significant activity against MRSA, MSSA, and mycobacterial strains. On the other hand, the absolute configuration of the new compound 17-deoxy-aspergillin PZ (1) isolated from Aspergillus sp. NCA276 was established via single-crystal X-ray crystallography. Also, the chemical analysis of the cocultures between Aspergillus and Cladosporium strains revealed the production of metabolites that were not present or were barely detected in the monocultures. Finally, molecular networking analysis of the LC-MS-MS/MS data for each fungus was used as a tool for the annotation of additional compounds, increasing the chemical knowledge on the corresponding fungal strains. Overall, this is the first systematic chemical study on fungi isolated from a sinkhole in Mexico.

Synthesis and structure-activity relationships of novel substituted 8-amino, 8-thio, and 1,8-pyrazole congeners of antitubercular rifamycin S and rifampin.

A series of rifamycin S and rifampin analogues incorporating substituted 8-amino, 8-thio, and 1,8-pyrazole substituents has been synthesized. The compounds were made by activation of the C-8 phenol as a sulfonate ester, followed by displacement with selected nitrogen and sulfur nucleophiles. The analogues were screened in assays to quantify their antitubercular activity under both aerobic and anaerobic conditions, and for inhibition of wild-type Mycobacterium tuberculosis (MTB) RNAP and rifamycin-resistant MTB RNAP (S450L) via an in vitro rolling circle transcription assay. Additionally, the MIC(90) values were determined for these analogues against Escherichia coli strains. Although none of the analogues displayed superior enzymatic or microbiological activity to their parent scaffolds, the results are consistent with the Rif C-8 hydroxyl acting as a hydrogen bond acceptor with S450 and that Rif resistance in the S450L mutant is due to loss of this hydrogen bond. Representative analogues were also evaluated in the human pregnane X receptor (PXR) activation assay.