Synthesis of Long-Chain β-Lactones and Their Antibacterial Activities against Pathogenic Mycobacteria

In the quest for new antibacterial agents, a series of novel long- and medium-chain mono- and disubstituted β-lactones was developed. Their activity against three pathogenic mycobacteria—M. abscessus, M. marinum, and M. tuberculosis—was assessed by the resazurin microtiter assay (REMA). Among the 16 β-lactones synthesized, only 3-hexadecyloxetan-2-one (VM005) exhibited promising activity against M. abscessus, whereas most of the β-lactones showed interesting activities against M. marinum, similar to that of the classical antibiotic, isoniazid. Regarding M. tuberculosis, six compounds were found to be active against this mycobacterium, with β-lactone VM008 [trans-(Z)-3-(hexadec-7-en-1-yl)-4-propyloxetan-2-one] being the best growth inhibitor. The promising antibacterial activities of the best compounds in this series suggest that these molecules may serve as leads for the development of much more efficient antimycobacterial agents.     

Antiparasitic Derivatives of the Furoquinoline Alkaloids Kokusaginine And Flindersiamine

We report the synthesis of 16 new compounds obtained from kokusaginine and flindersiamine, the main alkaloids isolated from the bark of Balfourodendron riedelianum. The activity of the compounds against axenic cultures of Trypanosoma cruzi epimastigtotes and trypomastigotes, as well as intracellular amastigotes, is described, together with their cytotoxic activity against three different human cell lines. The synthetic strategy for the preparation of the new compounds was based on the reactivity at the C4 position of the furoquinoline core towards nucleophiles. The new derivatives were synthesized by a Buchwald-Hartwig reaction, in most cases under green, solvent-free conditions. Compounds 1 c and 1 e displayed better in-vitro activity against trypomastigotes than benznidazole and nifurtimox (positive controls) with IC₅₀<4 μM. In addition, both compounds were not cytotoxic against the three human cell lines K562 (erytroleukimia), LM2 (breast cancer), and HaCat (keratinocyte). Interestingly, when evaluated against intracellular amastigotes, compound 1 c was able to significantly reduce the number of this parasite form, compared to the negative control.     

Modification of Biphenolic Anti-Bacterial to Achieve Broad-Spectrum Activity

The Gram-positive bacteria, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative bacteria, Acinetobacter baumannii, are pathogens responsible for millions of nosocomial infections worldwide. Due to the threat of bacteria evolving resistance to antibiotics, scientists are constantly looking for new classes of compounds to treat infectious diseases. The biphenolic analogs of honokiol that were most potent against oral bacteria had similar bioactivity against MRSA. However, all the compounds proved ineffective against A. baumannii. The inability to inhibit A. baumannii is due to the difficult-to-penetrate lipopolysaccharide-coated outer membrane that makes it challenging for antibiotics to enter Gram-negative bacteria. The C 2 scaffold was optimized from the inhibition of Gram-positive bacteria to broad-spectrum antibacterial compounds that inhibit the dangerous Gram-negative pathogen A. baumannii.     

Novel Hydrophilic Riminophenazines as Potent Antiprotozoal Agents

SAR studies on a set of novel hydrophilic C-2 aminopyridinyl riminophenazines bearing variously functionalized basic side chains at C-3 were conducted. The novel compounds were evaluated for in vitro activity against two different species of Leishmania promastigotes, intramacrophage Leishmania amastigotes, chloroquine-sensitive and chloroquine-resistant strains of P. falciparum, and also against mature-stage P. falciparum gametocytes. Their cytotoxicity was evaluated as well on BMDM cell lines. Most of the new compounds potently inhibited the growth of both genera of protozoa with IC₅₀ values in the high nanomolar range and good selectivities versus mammalian cells. Besides their potent activity against asexual intraerythrocytic stages of P. falciparum, three compounds showed potential as transmission-blocking agents. The key role of the hydrophilic C-2 aminopyridinyl substituent to improve the leishmanicidal activity and the influence of the length and the nature of the basic side chain on the antiprotozoal activity and cytotoxicity were underlined.     

Synthesis and in vitro Study of Artemisinin/Synthetic Peroxide-Based Hybrid Compounds against SARS-CoV-2 and Cancer

The newly emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cause life-threatening diseases in millions of people worldwide, in particular, in patients with cancer, and there is an urgent need for antiviral agents against this infection. While in vitro activities of artemisinins against SARS-CoV-2 and cancer have recently been demonstrated, no study of artemisinin and/or synthetic peroxide-based hybrid compounds active against both cancer and SARS-CoV-2 has been reported yet. However, the hybrid drug's properties (e. g., activity and/or selectivity) can be improved compared to its parent compounds and effective new agents can be obtained by modification/hybridization of existing drugs or bioactive natural products. In this study, a series of new artesunic acid and synthetic peroxide based new hybrids were synthesized and analyzed in vitro for the first time for their inhibitory activity against SARS-CoV-2 and leukemia cell lines. Several artesunic acid-derived hybrids exerted a similar or stronger potency against K562 leukemia cells (81–83 % inhibition values) than the reference drug doxorubicin (78 % inhibition value) and they were also more efficient than their parent compounds artesunic acid (49.2 % inhibition value) and quinoline derivative (5.5 % inhibition value). Interestingly, the same artesunic acid-quinoline hybrids also show inhibitory activity against SARS-CoV-2 in vitro (EC₅₀ 13–19 μm ) and no cytotoxic effects on Vero E6 cells (CC₅₀ up to 110 μM). These results provide a valuable basis for design of further artemisinin-derived hybrids to treat both cancer and SARS-CoV-2 infections.     

Antimicrobial activity of some fatty acid derivatives

Twelve fatty acid amide or ester derivatives were screened for antimicrobial activity against a grampositive bacterium,Staphylococcus aureus; a gramnegative bacterium,Escherichia coli; a mold, eitherAspergillus flavus orA. species; and a yeast, eitherCandida albicans orTorula species. These compounds were adducts of unsaturated fatty derivatives in which the addends were hexachlorocyclopentadiene, thiolacetic acid, bromotrichloromethane, or O,O-diethylphosphorodithioic acid. All of the new compounds appreciably inhibited the activity of at least one of the test organisms, and most of them showed activity against all four types of organisms. The hexachlorocyclopentadiene adduct of 2-(2-ethoxyethoxy)ethyl oleate was especially potent in this regard.     

Benzylaminoethylureido-Tailed Benzenesulfonamides Show Potent Inhibitory Activity against Bacterial Carbonic Anhydrases

A series of benzylaminoethylureido-tailed benzenesulfonamides was analyzed for their inhibition potential against bacterial carbonic anhydrases (CAs) such as VhCA α, β, and γ from Vibrio cholerae, and BpsCA β and γ-CAs from Burkholderia pseudomallei. Growing drug resistance against antibiotics demands alternative targets and mechanisms of action. As CA is essential for the survival of bacteria, such enzymes have the potential for developing new antibiotics. Most of the compounds presented excellent inhibition potential against VhCA γ compared to α and β, with K_i values in the range of 82.5–191.4 nM. Several sulfonamides exhibited excellent inhibition against BpsCA β with K_i values in the range of 394–742.8 nM. Recently it has been demonstrated that sufonamide CA inhibitors are effective against vancomycin-resistant enterococci. These data show that CA inhibition of pathogenic bacteria may lead to a new class of antibiotics.     

Quinoline-Dihydropyrimidin-2(1H)-one Hybrids: Synthesis,Biological Activity,and Mechanistic Studies

A novel class of quinoline-dihydropyrimidin-2(1H)-one (DHPM) hybrids was synthesized and in vitro antiplasmodial activity was evaluated against chloroquine sensitive (D10) and chloroquine resistant (Dd2) strains of Plasmodium falciparum, the human malaria parasite. The antiplasmodial activity was compared to previously reported DHPM based molecular hybrids. Dual mode of antiplasmodial action of the most active member has been evaluated through heme binding study and in silico docking in the active site of dihydrofolate enzymes (wild-type as well as mutant). Favourable pharmacokinetic parameters were predicted in the ADMET evaluation. The new hybrids were also tested against a number of DNA and RNA viruses. No antiviral activity was found, except for one hybrid that showed mild inhibitory activity against two strains of cytomegalovirus (AD-169 and Davis), The most active hybrid was found to be a selective inhibitor of the growth of P. falciparum as well as a modest inhibitor of varicella zoster virus in HEL cells. Cytotoxicity of all hybrids was assessed in HEL, HeLa, Vero, MDCK, and CRFK cell cultures.     

Focused directed evolution of pentaerythritol tetranitrate reductase by using automated anaerobic kinetic screening of site-saturated libraries

This work describes the development of an automated robotic platform for the rapid screening of enzyme variants generated from directed evolution studies of pentraerythritol tetranitrate (PETN) reductase, a target for industrial biocatalysis. By using a 96‐well format, near pure enzyme was recovered and was suitable for high throughput kinetic assays; this enabled rapid screening for improved and new activities from libraries of enzyme variants. Initial characterisation of several single site‐saturation libraries targeted at active site residues of PETN reductase, are described. Two mutants (T26S and W102F) were shown to have switched in substrate enantiopreference against substrates (E)‐2‐aryl‐1‐nitropropene and α‐methyl‐trans‐cinnamaldehyde, respectively, with an increase in ee (62 % (R) for W102F). In addition, the detection of mutants with weak activity against α,β‐unsaturated carboxylic acid substrates showed progress in the expansion of the substrate range of PETN reductase. These methods can readily be adapted for rapid evolution of enzyme variants with other oxidoreductase enzymes.     

Preparation and antibacterial activity of C2-benzaldehyde-C6-aniline double Schiff base derivatives of chitosan

C₂-benzaldehyde-C₆-aniline double Schiff base derivatives of chitosan were synthesized with positioning protection method for the first time. The structures and properties of the new synthesized products were characterized by Fourier transform infrared spectroscopy, ¹³C nuclear magnetic resonance, scanning electron microscope image, X-ray diffraction, and elemental analysis. The elemental analysis results indicated that the degrees of substitution of the products were from 39.6% to 48.2%. The synthesized compounds exhibited an excellent solubility in organic solvents. The antibacterial activities of all of the derivatives were tested in the experiment, and the results showed that the prepared chitosan derivatives had significantly improved antibacterial activity of chitosan and C₂-benzaldehyde Schiff bases of chitosan toward Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 35218). Antibacterial activity of the Schiff bases against E. coli differs from the substituent at the same position of different anilines and increases as the sequence aniline?>?p-toluidine?>?o-toluidine, and the antibacterial activity of the Schiff bases against S. aureus increases as the sequence p-toluidine?>?aniline?>?o-toluidine. The I_C50 of the C₂-benzaldehyde-C₆-aniline double Schiff base derivatives of chitosan against E. coli and S. aureus is 0.0035 and 0.0031?mg?L^?1, respectively, much lower than that of chitosan (0.0064?mg?L^?1) and C₂-benzaldehyde Schiff bases of chitosan (0.0054?mg?L^?1). The cytotoxicity test showed that compared with chitosan and C₂-benzaldehyde Schiff bases of chitosan, the prepared chitosan derivatives had lower cytotoxicity against SCG-7901. This paper provided a new method for the synthesis of Schiff bases of chitosan, which was enlightening.     

A Potent N-(piperidin-4-yl)-1H-pyrrole-2-carboxamide Inhibitor of Adenylyl Cyclase of G. lamblia: Biological Evaluation and Molecular Modelling Studies

In this work, we report a derivative of N-(piperidin-4-yl)-1H-pyrrole-2-carboxamide as a new inhibitor for adenylyl cyclase of Giardia lamblia which was obtained from a study using structural data of the nucleotidyl cyclase 1 (gNC1) of this parasite. For such a study, we developed a model for this specific enzyme by using homology techniques, which is the first model reported for gNC1 of G. lamblia. Our studies show that the new inhibitor has a competitive mechanism of action against this enzyme. 2-Hydroxyestradiol was used as the reference compound for comparative studies. Results in this work are important from two points of view. on the one hand, an experimentally corroborated model for gNC1 of G. lamblia obtained by molecular modelling is presented; on the other hand, the new inhibitor obtained is an undoubtedly excellent starting structure for the development of new metabolic inhibitors for G. lamblia.     

1‐(1H‐Indol‐3‐yl)ethanamine Derivatives as Potent Staphylococcus aureus NorA Efflux Pump Inhibitors

The synthesis of 37 1‐(1H‐indol‐3‐yl)ethanamine derivatives, including 12 new compounds, was achieved through a series of simple and efficient chemical modifications. These indole derivatives displayed modest or no intrinsic anti‐staphylococcal activity. By contrast, several of the compounds restored, in a concentration‐dependent manner, the antibacterial activity of ciprofloxacin against Staphylococcus aureus strains that were resistant to fluoroquinolones due to overexpression of the NorA efflux pump. Structure–activity relationships studies revealed that the indolic aldonitrones halogenated at position 5 of the indole core were the most efficient inhibitors of the S. aureus NorA efflux pump. Among the compounds, (Z)‐N‐benzylidene‐2‐(tert‐butoxycarbonylamino)‐1‐(5‐iodo‐1H‐indol‐3‐yl)ethanamine oxide led to a fourfold decrease of the ciprofloxacin minimum inhibitory concentration against the SA‐1199B strain when used at a concentration of 0.5 mg L ^?1. To the best of our knowledge, this activity is the highest reported to date for an indolic NorA inhibitor. In addition, a new antibacterial compound, tert‐butyl (2‐(3‐hydroxyureido)‐2‐(1H‐indol‐3‐yl)ethyl)carbamate, which is not toxic for human cells, was also found.     

Benzofuroxan Derivatives as Potent Agents against Multidrug-Resistant Mycobacterium tuberculosis

Tuberculosis (TB) is currently the leading cause of death related to infectious diseases worldwide, as reported by the World Health Organization. Moreover, the increasing number of multidrug-resistant tuberculosis (MDR-TB) cases has alarmed health agencies, warranting extensive efforts to discover novel drugs that are effective and also safe. In this study, 23 new compounds were synthesized and evaluated in vitro against the drug-resistant strains of M. tuberculosis. The compound 6-((3-fluoro-4-thiomorpholinophenyl)carbamoyl)benzo[c][1,2,5]oxadiazole 1-N-oxide ( 5 b ) was particularly remarkable in this regard as it demonstrated MIC₉₀ values below 0.28 μM against all the MDR strains evaluated, thus suggesting that this compound might have a different mechanism of action. Benzofuroxans are an attractive new class of anti-TB agents, exemplified by compound 5 b , with excellent potency against the replicating and drug-resistant strains of M. tuberculosis.     

Adsorption to the Surface of Hemozoin Crystals: Structure-Based Design and Synthesis of Amino-Phenoxazine β-Hematin Inhibitors

In silico adsorption of eight antimalarials that inhibit β-hematin (synthetic hemozoin) formation identified a primary binding site on the (001) face, which accommodates inhibitors via formation of predominantly π-π interactions. A good correlation (r²=0.64, P=0.017) between adsorption energies and the logarithm of β-hematin inhibitory activity was found for this face. Of 53 monocyclic, bicyclic and tricyclic scaffolds, the latter yielded the most favorable adsorption energies. Five new amino-phenoxazine compounds were pursued as β-hematin inhibitors based on adsorption behaviour. The 2-substituted phenoxazines show good to moderate β-hematin inhibitory activity (<100 μM) and Plasmodium falciparum blood stage activity against the 3D7 strain. N¹,N¹-diethyl-N⁴-(10H-phenoxazin-2-yl)pentane-1,4-diamine ( P2a ) is the most promising hit with IC₅₀ values of 4.7±0.6 and 0.64±0.05 μM, respectively. Adsorption energies are predictive of β-hematin inhibitory activity, and thus the in silico approach is a beneficial tool for structure-based development of new non-quinoline inhibitors.     

Antifeedants and Feeding Stimulants in Bark Extracts of Ten Woody Non-host Species of the Pine Weevil, Hylobius abietis

Bark of ten woody species, known to be rejected as a food source by the pine weevil, Hylobius abietis, were sequentially extracted by a Soxhlet apparatus with pentane followed by methanol. Species were alder (Alnus glutinosa), aspen (Populus tremula), beech (Fagus sylvatica), guelder rose (Viburnum opulus), holly (Ilex aquifolium), horse chestnut (Aesculus hippocastanum), lilac (Syringa vulgaris), spindle tree (Evonymus europaeus), walnut (Juglans regia), and yew (Taxus baccata). Bark of each species was collected in southern Scandinavia during the summer. Resulting extracts were tested for antifeedant activity against the pine weevil by a micro-feeding choice assay. At a dose corresponding to that in the bark, methanol extracts from Aesculus, Taxus, Ilex, and Populus were antifeedant active, while pentane extracts of Aesculus, Fagus, Syringa, and Viburnum were stimulatory. Four known antifeedants against H. abietis, the straight-chained carboxylic acids, hexanoic and nonanoic acid (C6 and C9), carvone, and carvacrol were identified by gas chromatography (GC)–mass spectrometry (MS) in several extracts. The major constituents were identified and tested for feeding deterrence. The aromatic compounds benzyl alcohol and 2-phenylethanol are new non-host plant-derived feeding deterrents for the pine weevil. Additionally, two feeding stimulants, β-sitosterol and 5-(hydroxymethyl)-2-furaldehyde, were identified. One active methanol extract of Aesculus bark was sequentially fractionated by liquid chromatography, and major compounds were tentatively identified as branched alcohols and esters of hexanoic acid. Five commercially available hexanoate esters and two commercially available branched alcohols were identified as new active antifeedants. Both stimulatory and inhibiting compounds were found in the same extracts and co-eluted in the same or adjacent fractions. The mix of semiochemicals of opposite activity in each extract or fraction could explain the stimulatory-, inhibitory-, or sometimes neutral activity. Generally, such co-occurrence confounds the isolation of antifeedants.     

A Fluorescence-Based Assay for Screening β-Lactams Targeting the Mycobacterium tuberculosis Transpeptidase LdtMt2

Mycobacterium tuberculosis l,d -transpeptidases (Ldts), which are involved in cell-wall biosynthesis, have emerged as promising targets for the treatment of tuberculosis. However, an efficient method for testing inhibition of these enzymes is not currently available. We present a fluorescence-based assay for Ldt_Mt2, which is suitable for high-throughput screening. Two fluorogenic probes were identified that release a fluorophore upon reaction with Ldt_Mt2, thus making it possible to assess the availability of the catalytic site in the presence of inhibitors. The assay was applied to a panel of β-lactam antibiotics and related inhibitors; the results validate observations that the (carba)penem subclass of β-lactams are more potent Ldt inhibitors than other β-lactam classes, though unexpected variations in potency were observed. The method will enable systematic structure–activity relationship studies on Ldts, thereby facilitating the identification of new antibiotics active against M. tuberculosis.     

From Antidiabetic to Antifungal: Discovery of Highly Potent Triazole–Thiazolidinedione Hybrids as Novel Antifungal Agents

In an attempt to discover a new generation of triazole antifungal agents, a series of triazole–thiazolidinedione hybrids were designed and synthesized by molecular hybridization of the antifungal agent fluconazole and rosiglitazone (an antidiabetic). Most of the target compounds showed good to excellent inhibitory activity against a variety of clinically important fungal pathogens. In particular, compounds (Z)‐5‐(2,4‐dichlorobenzylidene)‐3‐(2‐(2,4‐difluorophenyl)‐2‐hydroxy‐3‐(1H‐1,2,4‐triazol‐1‐yl)propyl)thiazolidine‐2,4‐dione) ( 15 c ), (Z)‐3‐(2‐(2,4‐difluorophenyl)‐2‐hydroxy‐3‐(1H‐1,2,4‐triazol‐1‐yl)propyl)‐5‐(furan‐3‐ylmethylene)thiazolidine‐2,4‐dione ( 15 j ), and (Z)‐3‐(2‐(2,4‐difluorophenyl)‐2‐hydroxy‐3‐(1H‐1,2,4‐triazol‐1‐yl)propyl)‐5‐(furan‐3‐ylmethylene)thiazolidine‐2,4‐dione ( 15 r ) were highly active against Candida albicans, with MIC₈₀ values in the range of 0.03–0.15 μM . Moreover, compounds 15 j and 15 r were found to be effective against four fluconazole‐resistant clinical isolates; these two compounds are particularly promising antifungal leads for further optimization. Molecular docking studies revealed that the hydrogen bonding interactions between thiazolidinedione and CYP51 from C. albicans are important for antifungal activity. This study also demonstrates the effectiveness of molecular hybridization in antifungal drug discovery.     

Bis(N-picolinamido)cobalt(II) Complexes Display Antifungal Activity toward Candida albicans and Aspergillus fumigatus

This report highlights the synthesis and characterization of ten new bis(N-picolinamido)cobalt(II) complexes of the type [(L)₂CoX₂]^0/2+, whereby L=N-picolinamide ligand and X=diisothiocyanato (−NCS), dichlorido (−Cl) or diaqua (−OH₂) ligands. Single crystal X-ray (SC-XRD) analysis for nine of the structures are reported and confirm the picolinamide ligand is bound to the Co(II) center through a neutral N,O binding mode. With the addition of powder X-ray diffraction (PXRD), we have confirmed the cis and trans ligand arrangements of each complex. All complexes were screened against several fungal species and show increased antifungal activity. Notably, these complexes had significant activity against strains of Candida albicans and Aspergillus fumigatus, with several compounds exhibiting growth inhibition of >80 %, and onecompound inhibiting Aspergillus fumigatus hyphal growth by >90 %. Conversely, no antifungal activity was exhibited toward Cryptococcus neoformans and no cytotoxicity towards mammalian cell lines.     

Challenges Based on Antiplasmodial and Antiviral Activities of 7-Chloro-4-aminoquinoline Derivatives

We report the structural functionalization of the terminal amino group of N¹-(7-chloroquinolin-4-yl) butane-1,4-diamine, leading to a series of 7-chloro-4-aminoquinoline derivatives, and their evaluation as potent anti-malarial and anti-viral agents. Some compounds exhibited promising anti-malarial effects against the Plasmodium falciparum 3D7 (chloroquine-sensitive) and Dd2 (chloroquine-resistant) strains. In addition, these compounds were assayed in vitro against influenza A virus (IAV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Compound 5 h , bearing an N-mesityl thiourea group, displayed pronounced anti-infectious effects against malaria, IAV, and SARS-CoV-2. These results provide new insights into drug discovery for the prevention or treatment of malaria and virus co-infection.