N-substituted 5-amino-6-methylpyrazine-2,3-dicarbonitriles: microwave-assisted synthesis and biological properties

Construction of 5-(Alkylamino)-6-aryl/alkylpyrazine-2,3-dicarbonitriles via the One-Pot Reaction of Alkyl Isocyanides with Aryl/Alkyl Carbonyl Chlorides and Diaminomaleonitrile: Fluorescence and Antimicrobial Activity Evaluation

5-(Alkylamino)-6-aryl/alkylpyrazine-2,3-dicarbonitriles were successfully synthesized in good to moderate yields by reacting alkyl isocyanides with aryl/alkyl carbonyl chlorides, followed by the addition of diaminomaleonitrile. The synthesized pyrazines were fully characterized in this investigation, and X-ray crystal structure analysis was performed on some derivatives. The antibacterial and antifungal activities of the newly synthesized pyrazine-2,3-dicarbonitriles were assessed in addition to their UV and fluorescence results. All the compounds showed similar UV-Vis spectral features with absorption peaks (λ_max) around 267, 303, and 373 nm.

Halogenated 1-Hydroxynaphthalene-2-Carboxanilides Affecting Photosynthetic Electron Transport in Photosystem II

Series of seventeen new multihalogenated 1-hydroxynaphthalene-2-carboxanilides was prepared and characterized. All the compounds were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. 1-Hydroxy-N-phenylnaphthalene-2-carboxamides substituted in the anilide part by 3,5-dichloro-, 4-bromo-3-chloro-, 2,5-dibromo- and 3,4,5-trichloro atoms were the most potent PET inhibitors (IC₅₀ = 5.2, 6.7, 7.6 and 8.0 µM, respectively). The inhibitory activity of these compounds depends on the position and the type of halogen substituents, i.e., on lipophilicity and electronic properties of individual substituents of the anilide part of the molecule. Interactions of the studied compounds with chlorophyll a and aromatic amino acids present in pigment-protein complexes mainly in PS II were documented by fluorescence spectroscopy. The section between P₆₈₀ and plastoquinone Q_B in the PET chain occurring on the acceptor side of PS II can be suggested as the site of action of the compounds. The structure-activity relationships are discussed.

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.

Antimycobacterial N-alkoxyphenylhydroxynaphthalenecarboxamides affecting photosystem II

N-(Alkoxyphenyl)-2-hydroxynaphthalene-1-carboxamides (series A) and N-(alkoxyphenyl)-1-hydroxynaphthalene-2-carboxamides (series B) affecting photosystem (PS) II inhibited photosynthetic electron transport (PET) in spinach chloroplasts. Their inhibitory activity depended on the compound lipophilicity as well as on the position of the alkoxy substituent. The most potent PET inhibitors were 2-hydroxy-N-phenylnaphthalene-1-carboxamide and N-[3-(but-2-yloxy)phenyl]-2-hydroxynaphthalene-1-carboxamide within series A (IC₅₀=28.9 and 42.5µM, respectively) and 1-hydroxy-N-(3-propoxyphenyl)naphthalene-2-carboxamide and 1-hydroxy-N-(3-ethoxyphenyl)-naphthalene-2-carboxamide (IC₅₀=2.0 and 3.1µM, respectively) within series B. The inhibitory activity of C'₍₃₎ or C'₍₄₎ alkoxy substituted compounds of series B was considerably higher than that of C'₍₂₎ ones within series A. The PET-inhibiting activities of both series were compared with the PET inhibition of isomeric N-alkoxyphenyl-3-hydroxynaphthalene-2-carboxamides (series C) reported recently. Interactions of the studied compounds with chlorophyll a and aromatic amino acids present in pigment-protein complexes mainly in PS II were documented by fluorescence spectroscopy. The section between P₆₈₀ and plastoquinone Q_B in the PET chain occurring on the acceptor side of PSII can be suggested as the site of action of the compounds.

Synthesis of Novel Pyrazinamide Derivatives Based on 3-Chloropyrazine-2-carboxamide and Their Antimicrobial Evaluation

Aminodehalogenation of 3-chloropyrazine-2-carboxamide with variously substituted benzylamines yielded a series of fifteen 3-benzylaminopyrazine-2-carboxamides. Four compounds possessed in vitro whole cell activity against Mycobacterium tuberculosis H37R_v that was at least equivalent to that of the standard pyrazinamide. MIC values ranged from 6 to 42 µM. The best MIC (6 µM) was displayed by 3-[(4-methylbenzyl)amino]pyrazine-2-carboxamide (8) that also showed low cytotoxicity in the HepG2 cell line (IC₅₀ ≥ 250 µM). Only moderate activity against Enterococcus faecalis and Staphylococcus aureus was observed. No activity was detected against any of tested fungal strains. Molecular docking with mycobacterial enoyl-ACP reductase (InhA) was performed to investigate the possible target of the prepared compounds. Active compounds shared common binding interactions of known InhA inhibitors. Antimycobacterial activity of the title compounds was compared to the previously published benzylamino-substituted pyrazines with differing substitution on the pyrazine core (carbonitrile moiety). The title series possessed comparable activity and lower cytotoxicity than molecules containing a carbonitrile group on the pyrazine ring.

Synthesis and Herbicidal Activity of New Hydrazide and Hydrazonoyl Derivatives

Three new hydrazide and five new hydrazonoyl derivatives were synthesized. The chemical structures of these compounds were confirmed by ¹H-NMR, IR spectroscopy and elemental analysis. The prepared compounds were tested for their activity to inhibit photosynthetic electron transport in spinach chloroplasts and growth of the green algae Chlorella vulgaris. IC₅₀ values of these compounds varied in wide range, from a strong to no inhibitory effect. EPR spectroscopy showed that the active compounds interfered with intermediates Z^•/D^•, which are localized on the donor side of photosystem II. Fluorescence spectroscopy suggested that the mechanism of inhibitory action of the prepared compounds possibly involves interactions with aromatic amino acids present in photosynthetic proteins.

Novel pyrazine analogs of chalcones: synthesis and evaluation of their antifungal and antimycobacterial activity

Infectious diseases, such as tuberculosis and invasive mycoses, represent serious health problems. As a part of our long-term efforts to find new agents for the treatment of these diseases, a new series of pyrazine analogs of chalcones bearing an isopropyl group in position 5 of the pyrazine ring was prepared. The structures of the compounds were corroborated by IR and NMR spectroscopy and their purity confirmed by elemental analysis. The susceptibility of eight fungal strains to the studied compounds was tested. The results have been compared with the activity of some previously reported propyl derivatives. The only strain that was susceptible to the studied compounds was Trichophyton mentagrophytes. It was found that replacing a non-branched propyl with a branched isopropyl did not have a decisive and unequivocal influence on the in vitro antifungal activity against T. mentagrophytes. In vitro activity against Trichophyton mentagrophytes comparable with that of fluconazole was exhibited by nitro-substituted derivatives. Unfortunately, no compound exhibited efficacy comparable with that of terbinafine, which is the most widely used agent for treating mycoses caused by dermatophytes. Some of the prepared compounds were assayed for antimycobacterial activity against M. tuberculosis H₃₇Rv. The highest potency was also displayed by nitro-substituted compounds. The results of the present study are in a good agreement with our previous findings and confirm the positive influence of electron-withdrawing groups on the B-ring of chalcones on the antifungal and antimycobacterial activity of these compounds.

Synthesis, antimycobacterial and antifungal evaluation of some new 1-ethyl-5-(hetero)aryl-6-styryl-1,6-dihydropyrazine-2,3-dicarbonitriles

The Petasis reaction of 6-hydroxy adducts of 1-alkyl-2,3-dicyano-5-arylpyrazinium salts with trans-styrylboronic acids proved to proceed smoothly at room temperature to give the corresponding 5-(hetero)aryl-6-styryl substituted 1,6-dihydropyrazine derivatives. Also it has been found that C(6) unsubstituted 1,6-dihydro- or 1,4,5,6-tetrahydropyrazine derivatives can be easy prepared in high yields from the corresponding pyrazinium salts by reduction with triethylsilane. All synthesized compounds were screened in vitro for their antifungal activities against seven pathogenic fungal strains and antimycobacterial activities against Mycobacterium tuberculosis H37Rv, avium, terrae and multi-drug-resistant strains isolated from tuberculosis patients in the Ural region (Russia).

New potentially active pyrazinamide derivatives synthesized under microwave conditions

A series of 18 N-alkyl substituted 3-aminopyrazine-2-carboxamides was prepared in this work according to previously experimentally set and proven conditions using microwave assisted synthesis methodology. This approach for the aminodehalogenation reaction was chosen due to higher yields and shorter reaction times compared to organic reactions with conventional heating. Antimycobacterial, antibacterial, antifungal and photosynthetic electron transport (PET) inhibiting in vitro activities of these compounds were investigated. Experiments for the determination of lipophilicity were also performed. Only a small number of substances with alicyclic side chain showed activity against fungi which was the same or higher than standards and the biological efficacy of the compounds increased with rising lipophilicity. Nine pyrazinamide derivatives also inhibited PET in spinach chloroplasts and the IC₅₀ values of these compounds varied in the range from 14.3 to 1590.0 μmol/L. The inhibitory activity was connected not only with the lipophilicity, but also with the presence of secondary amine fragment bounded to the pyrazine ring. Structure-activity relationships are discussed as well.