Substituted pyrazinecarboxamides: synthesis and biological evaluation

Improving Antimicrobial Activity and Physico-Chemical Properties by Isosteric Replacement of 2-Aminothiazole with 2-Aminooxazole

Antimicrobial drug resistance is currently one of the most critical health issues. Pathogens resistant to last-resort antibiotics are increasing, and very few effective antibacterial agents have been introduced in recent years. The promising drug candidates are often discontinued in the primary stages of the drug discovery pipeline due to their unspecific reactivity (PAINS), toxicity, insufficient stability, or low water solubility. In this work, we investigated a series of substituted N-oxazolyl- and N-thiazolylcarboxamides of various pyridinecarboxylic acids. Final compounds were tested against several microbial species. In general, oxazole-containing compounds showed high activity against mycobacteria, especially Mycobacterium tuberculosis (best MIC_H37Ra = 3.13 µg/mL), including the multidrug-resistant strains. Promising activities against various bacterial and fungal strains were also observed. None of the compounds was significantly cytotoxic against the HepG2 cell line. Experimental measurement of lipophilicity parameter log k’_w and water solubility (log S) confirmed significantly (typically two orders in logarithmic scale) increased hydrophilicity/water solubility of oxazole derivatives in comparison with their thiazole isosteres. Mycobacterial β-ketoacyl-acyl carrier protein synthase III (FabH) was suggested as a probable target by molecular docking and molecular dynamics simulations.

A new short synthesis route for favipiravir and its analogue: Their tautomerization behaviour

Halogen substitution in a pyrazine ring is achieved in an efficient manner. The solid state data revealed the formation of two types of halogen bonding in the structures.

Design, synthesis and biological evaluation of substituted 3-amino-N-(thiazol-2-yl)pyrazine-2-carboxamides as inhibitors of mycobacterial methionine aminopeptidase 1

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) is the number one cause of deaths due to a single infectious agent worldwide. The treatment of TB is lengthy and often complicated by the increasing drug resistance. New compounds with new mechanisms of action are therefore needed. We present the design, synthesis, and biological evaluation of pyrazine-based inhibitors of a prominent antimycobacterial drug target - mycobacterial methionine aminopeptidase 1 (MtMetAP1). The inhibitory activities of the presented compounds were evaluated against the MtMetAP1a isoform, and all derivatives were tested against a broad spectrum of myco(bacteria) and fungi. The cytotoxicity of the compounds was also investigated using Hep G2 cell lines. Overall, high inhibition of the isolated enzyme was observed for 3-substituted N-(thiazol-2-yl)pyrazine-2-carboxamides, particularly when the substituent was represented by 2-substituted benzamide. The extent of inhibition was strongly dependent on the used metal cofactor. The highest inhibition was seen in the presence of Ni²⁺. Several compounds also showed mediocre in vitro potency against Mtb (both Mtb H37Ra and H37Rv). Despite the structural similarities of bacterial and fungal MetAP1 to mycobacterial MtMetAP1, title compounds did not exert antibacterial nor antifungal activity. The reasons behind the higher activity of 2-substituted benzamido derivatives, as well as the correlation of enzyme inhibition with the in vitro growth inhibition activity is discussed.

When biomolecules meet 2-hydrazinopyrazine: from theory through experiment to molecular levels using a wide spectrum of techniques

The design of drug structures that are non-toxic, easily transported and permeable to cellular barriers is currently one of the most growing research trends. Indeed, the structural similarity of 2-hydrazinopyrazine (2HP) to pyrazinamide, which has been successfully used in anti-tuberculosis therapy, makes 2HP a promising research object. Thus, herein, a complete analysis of the structure of 2HP and its physicochemical and cytotoxic properties was performed. Calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) binding studies were conducted, which demonstrated the higher affinity of 2HP to BSA. Furthermore, cytotoxicity tests were performed, which proved that 2HP was non-toxic to human skin keratinocyte cells. Accordingly, 2HP was initially classified as a compound with potential application. Physicochemical investigations were performed using a wide range of experiments, which were supported by DFT calculations using the B3LYP functional and 6-311+G** basis set. The good correlation, high quality and correctness of the obtained parameters were proven although the data was obtained using independent techniques. Additionally, 42 tautomeric (prototrophic) forms of 2HP were found by searching the conformational hyperspace. The most energy stable 2HP conformer structure and the partial charge distribution were established. The preferred 2HP ionic forms preferred were presented, and models of the equilibrium occurring in aqueous solution were proposed. The hydrophilic character of 2HP was established based on the partition coefficient values determined by both experiment and theory. The PCM and SMD solvent models of water and n-octanol were used.

Structure, ionic forms, hydrophilic and non-cytotoxic character of 2-hydrazinopyrazine with stronger affinity to BSA than DNA were proved.

Seeking potent anti-tubercular agents: design and synthesis of substituted-N-(6-(4-(pyrazine-2-carbonyl)piperazine/homopiperazine-1-yl)pyridin-3-yl)benzamide derivatives as anti-tubercular agents

We herein report 27 pyrazinamide analogues as anti-tubercular agents, of which six exhibited excellent activity with IC₅₀ ≤ 2.18 μM and these were less toxic against HEK 293 cells.

Substituted N-(Pyrazin-2-yl)benzenesulfonamides; Synthesis, Anti-Infective Evaluation, Cytotoxicity, and In Silico Studies

We prepared a series of substituted N-(pyrazin-2-yl)benzenesulfonamides as an attempt to investigate the effect of different linkers connecting pyrazine to benzene cores on antimicrobial activity when compared to our previous compounds of amide or retro-amide linker type. Only two compounds, 4-amino-N-(pyrazin-2-yl)benzenesulfonamide (MIC = 6.25 μg/mL, 25 μM) and 4-amino-N-(6-chloropyrazin-2-yl)benzenesulfonamide (MIC = 6.25 μg/mL, 22 μM) exerted good antitubercular activity against M. tuberculosis H37Rv. However, they were excluded from the comparison as they-unlike the other compounds-possessed the pharmacophore for the inhibition of folate pathway, which was proven by docking studies. We performed target fishing, where we identified matrix metalloproteinase-8 as a promising target for our title compounds that is worth future exploration.

Design, Synthesis and Evaluation of N-pyrazinylbenzamides as Potential Antimycobacterial Agents

Three series of N-(pyrazin-2-yl)benzamides were designed as retro-amide analogues of previously published N-phenylpyrazine-2-carboxamides with in vitro antimycobacterial activity. The synthesized retro-amides were evaluated for in vitro growth inhibiting activity against Mycobacterium tuberculosis H37Rv (Mtb), three non-tuberculous mycobacterial strains (M. avium, M. kansasii, M. smegmatis) and selected bacterial and fungal strains of clinical importance. Regarding activity against Mtb, most N-pyrazinylbenzamides (retro-amides) possessed lower or no activity compared to the corresponding N-phenylpyrazine-2-carboxamides with the same substitution pattern. However, the active retro-amides tended to have lower HepG2 cytotoxicity and better selectivity. Derivatives with 5-chloro substitution on the pyrazine ring were generally more active compared to their 6-cloro positional isomers or non-chlorinated analogues. The best antimycobacterial activity against Mtb was found in N-(5-chloropyrazin-2-yl)benzamides with short alkyl (2h: R² = Me; 2i: R² = Et) in position 4 of the benzene ring (MIC = 6.25 and 3.13 µg/mL, respectively, with SI > 10). N-(5-Chloropyrazin-2-yl)benzamides with hydroxy substitution (2b: R² = 2-OH; 2d: R² = 4-OH) on the benzene ring or their acetylated synthetic precursors possessed the broadest spectrum of activity, being active in all three groups of mycobacterial, bacterial and fungal strains. The substantial differences in in silico calculated properties (hydrogen-bond pattern analysis, molecular electrostatic potential, HOMO and LUMO) can justify the differences in biological activities between N-pyrazinylbenzamides and N-phenylpyrazine-2-carboxamides.

Design, synthesis and antimycobacterial activity of hybrid molecules combining pyrazinamide with a 4-phenylthiazol-2-amine scaffold

Hybrid compounds based on a combination of the first-line antitubercular pyrazinamide (PZA) and a formerly identified antimycobacterial scaffold of 4-arylthiazol-2-amine were designed. Eighteen compounds were prepared, characterized and tested for in vitro growth inhibition activity against M. tuberculosis H37Rv, M. kansasii, M. avium and M. smegmatis by Microplate Alamar Blue Assay at neutral pH. Active compounds were tested for in vitro cytotoxicity in the human hepatocellular carcinoma cell line (HepG2). The most active 6-chloro-N-[4-(4-fluorophenyl)thiazol-2-yl]pyrazine-2-carboxamide (9b) also had the broadest spectrum of activity and inhibited M. tuberculosis, M. kansasii, and M. avium with MIC = 0.78 μg mL^-1 (2.3 μM) and a selectivity index related to HepG2 cells of SI > 20. Structure-activity relationships within the series are discussed. Based on its structural similarity to known inhibitors and the results of a molecular docking study, we suggest mycobacterial beta-ketoacyl-(acyl-carrier-protein) synthase III (FabH) as a potential target.

Effect of Selected Pyrazine Derivatives on the Production of Phenolics and Rutin in Urtica dioica and Fagopyrum esculentum

The effect of four pyrazine derivatives on the content of phenolic compounds in Urtica dioica L. and rutin in Fagopyrum esculentum Moench was studied. Pyrazine derivatives H1 and H2 were used on U. dioica, and derivatives S1 and S2 on F. esculentum, both separately and in combination with urea. The content of phenolic compounds in the stems of U. dioica after treatment with H2 at a concentration of 10−3 M significantly increased compared with the control and to a lower concentration of the same pyrazine derivative. In the case of S1 and S2 for F. esculentum, rutin content also increased in stems, mainly after treatment together with urea. By contrast, rutin and phenolics contents in the leaves did not change in comparison with controls after application of H1, H2, S1 and S2. Treatment with H1 and H2 in two chosen concentrations resulted in a significant increase in the net photosynthetic rate, transpiration rate and stomatal conductance. A slight increase in the rate of photosynthesis was observed also after application of variants of S1 and S1 with urea. Pyrazine derivatives did not show any effect on either the relative content of chlorophyll or chlorophyll fluorescence. A slight weight reduction of above ground biomass was shown only after application of S1 and S2. Dark necrosis on the edges and center of the leaves was observed in all treated plants after pyrazine application. The results suggest that all the pyrazine derivatives possess herbicidal effects.

Crystalline pyrazine-2-amidoxime isolated by diffusion method and its structural and behavioral analysis in the context of crystal engineering and microbiological activity

The physicochemical characterizations of PAOX were obtained both in solid-state and solution, and its two anti-conformers were observed in the X-ray. Its antimicrobial properties were tested against reference strains of bacteria and yeast.

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).

Anti-infective and herbicidal activity of N-substituted 2-aminobenzothiazoles

In this study, a series of N-substituted 2-aminobenzothiazoles was prepared according to a recently developed method. Twelve compounds were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Primary in vitro screening of the discussed compounds was also performed against fungal, bacterial and mycobacterial species. The biological activities of some compounds were comparable or higher than the standards phenoxymethylpenicillin or pyrazinamide. The most effective compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. For all compounds, the structure-activity relationships are discussed.

Investigating the spectrum of biological activity of substituted quinoline-2-carboxamides and their isosteres

In this study, a series of thirty-five substituted quinoline-2-carboxamides and thirty-three substituted naphthalene-2-carboxamides were prepared and characterized. They were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Primary in vitro screening of the synthesized compounds was also performed against four mycobacterial species. N-Cycloheptylquinoline-2-carboxamide, N-cyclohexylquinoline-2-carboxamide and N-(2-phenylethyl)quinoline-2-carboxamide showed higher activity against M. tuberculosis than the standards isoniazid or pyrazinamide and 2-(pyrrolidin-1-ylcarbonyl)quinoline and 1-(2-naphthoyl)pyrrolidine expressed higher activity against M. kansasii and M. avium paratuberculosis than the standards isoniazid or pyrazinamide. The most effective antimycobacterial compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. The PET-inhibiting activity expressed by IC₅₀ value of the most active compound N-benzyl-2-naphthamide was 7.5 μmol/L. For all compounds, the structure-activity relationships are discussed.

Synthesis and characterization of (Z)-5-arylmethylidene-rhodanines with photosynthesis-inhibiting properties

A series of rhodanine derivatives was prepared. The synthetic approach, analytical and spectroscopic data of all synthesized compounds are presented. Lipophilicity of all the discussed rhodanine derivatives was analyzed using the RP-HPLC method. The compounds were tested for their ability to inhibit photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts and reduce chlorophyll content in freshwater alga Chlorella vulgaris. Structure-activity relationships between the chemical structure, physical properties and biological activities of the evaluated compounds are discussed. For majority of the tested compounds the lipophilicity of the compound and not electronic properties of the R¹ substituent were decisive for PET-inhibiting activity. The most potent PET inhibitor was (5Z)-5-(4-bromobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (IC₅₀ = 3.0 μmol/L) and the highest antialgal activity was exhibited by (5Z)-5-(4-chlorobenzylidene)-2-thioxo-1,3-thiazolidin-4-one (IC₅₀ = 1.3 μmol/L).

Investigating spectrum of biological activity of 4- and 5-chloro-2-hydroxy-N-[2-(arylamino)-1-alkyl-2-oxoethyl]benzamides

In this study, a series of twenty-two 5-chloro-2-hydroxy-N-[2-(arylamino)-1-alkyl-2-oxoethyl]benzamides and ten 4-chloro-2-hydroxy-N-[2-(arylamino)-1-alkyl-2-oxoethyl]benzamides is described. The compounds were analyzed using RP-HPLC to determine lipophilicity. Primary in vitro screening of the synthesized compounds was performed against mycobacterial, bacterial and fungal strains. They were also evaluated for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. The compounds showed biological activity comparable with or higher than the standards isoniazid, fluconazole, penicillin G or ciprofloxacin. For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds as well as their structure-activity relationships are discussed.

Synthesis, antimycobacterial, antifungal and photosynthesis-inhibiting activity of chlorinated N-phenylpyrazine-2-carboxamides

A series of sixteen pyrazinamide analogues with the -CONH- linker connecting the pyrazine and benzene rings was synthesized by the condensation of chlorides of substituted pyrazinecarboxylic acids with ring-substituted (chlorine) anilines. The prepared compounds were characterized and evaluated for their antimycobacterial and antifungal activity, and for their ability to inhibit photosynthetic electron transport (PET). 6-Chloro-N-(4-chlorophenyl)pyrazine-2-carboxamide manifested the highest activity against Mycobacterium tuberculosis strain H37Rv (65% inhibition at 6.25 μg/mL). The highest antifungal effect against Trichophyton mentagrophytes, the most susceptible fungal strain tested, was found for 6-chloro-5-tert-butyl-N-(3,4-dichlorophenyl)pyrazine-2-carboxamide (MIC = 62.5 μmol/L). 6-Chloro-5-tert-butyl-N-(4-chlorophenyl)pyrazine-2-carboxamide showed the highest PET inhibition in spinach chloroplasts (Spinacia oleracea L.) chloroplasts (IC₅₀ = 43.0 μmol/L). For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds as well as their structure–activity relationships are discussed.

Investigating the spectrum of biological activity of ring-substituted salicylanilides and carbamoylphenylcarbamates

In this study, a series of twelve ring-substituted salicylanilides and carbamoylphenylcarbamates were prepared and characterized. The compounds were analyzed using RP-HPLC to determine lipophilicity. They were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Moreover, their site of action in the photosynthetic apparatus was determined. Primary in vitro screening of the synthesized compounds was also performed against mycobacterial, bacterial and fungal strains. Several compounds showed biological activity comparable with or higher than the standards 3-(3,4-dichlorophenyl)-1,1-dimethylurea, isoniazid, penicillin G, ciprofloxacin or fluconazole. The most active compounds showed minimal anti-proliferative activity against human cells in culture, indicating they would have low cytotoxicity. For all compounds, the relationships between lipophilicity and the chemical structure are discussed.

Investigating the activity spectrum for ring-substituted 8-hydroxyquinolines

In this study, a series of fourteen ring-substituted 8-hydroxyquinoline derivatives were prepared. The synthesis procedures are presented. The compounds were analyzed using RP-HPLC to determine lipophilicity. They were tested for their activity related to inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Primary in vitro screening of the synthesized compounds was also performed against four mycobacterial strains and against eight fungal strains. Several compounds showed biological activity comparable with or higher than the standards isoniazid or fluconazole. For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds are discussed.

Investigating biological activity spectrum for novel styrylquinazoline analogues

In this study, series of ring-substituted 2-styrylquinazolin-4(3H)-one and 4-chloro-2-styrylquinazoline derivatives were prepared. The syntheses of the discussed compounds are presented. The compounds were analyzed by RP-HPLC to determine lipophilicity. They were tested for their inhibitory activity on photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Primary in vitro screening of the synthesized compounds was also performed against four mycobacterial strains and against eight fungal strains. Several compounds showed biological activity comparable with or higher than that of the standard isoniazid. It was found that the electronic properties of the R substituent, and not the total lipophilicity of the compound, were decisive for the photosynthesis-inhibiting activity of tested compounds.

Substituted N-Phenylpyrazine-2-carboxamides: synthesis and antimycobacterial evaluation

The condensation of chlorides of substituted pyrazinecarboxylic acids with ring-substituted anilines yielded twelve substituted pyrazinecarboxylic acid amides. The synthetic approach, analytical, and lipophilicity data of the newly synthesized compounds are presented. Two antituberculosis assays were used. Firstly, the antimycobacterial activity against four different Mycobacterium strains in a series of pyrazine derivatives was investigated. Secondly, the antimycobacterial evaluation was performed at the Tuberculosis Antimicrobial Acquisition and Coordinating Facility (TAACF) program. Interesting in vitro antimycobacterial activity was found, N-(3-iodo-4-methyl-phenyl)pyrazine-2-carboxamide (9) was most active derivative compound against M. tuberculosis (MIC < 2.0 μmol/L), while another iodo derivative 5-tert-butyl-6-chloro-N-(3-iodo-4-methyl-phenyl)pyrazine-2-carboxamide (12) was the most active compound in the TAACF antituberculosis screening program (IC₉₀ = 0.819 µg/mL).

New antituberculotics originated from salicylanilides with promising in vitro activity against atypical mycobacterial strains

A new series of 30 N-protected amino acid esters were prepared as a part of ongoing search for new anti-tuberculosis active salicylanilides. The esters possess high in vitro activity against Mycobacterium tuberculosis, Mycobacterium avium, and two strains of Mycobacterium kansasii, where one is an isolate from the patient, with MIC in the range 1-32 micromol/L for all tested strains. The prepared esters can be considered as prodrugs with better bio-availability and as more efficient transport forms through the mycobacterial cell membranes due to the higher lipophilicity. The experimental and calculated lipophilicity, stability, antituberculotic activity, cytotoxicity as well as the quantitative structure-activity relationships (QSARs) explored by the Intelligent Problem Solver (IPS) in Trajan Neural Network Simulator 6.0 are presented.

Ring-substituted 4-hydroxy-1H-quinolin-2-ones: preparation and biological activity

In the study, a series of twelve ring-substituted 4-hydroxy-1H-quinolin-2-one derivatives were prepared. The procedures for synthesis of the compounds are presented. The compounds were analyzed using RP-HPLC to determine lipophilicity and tested for their photosynthesis-inhibiting activity using spinach (Spinacia oleracea L.) chloroplasts. All the synthesized compounds were also evaluated for antifungal activity using in vitro screening with eight fungal strains. For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds are discussed, as well as their structure-activity relationships (SAR).

Identification and characterization of thiosemicarbazones with antifungal and antitumor effects: cellular iron chelation mediating cytotoxic activity

Thiosemicarbazones derived from acetylpyrazines were prepared by condensing an acetylpyrazine or a ring-substituted acetylpyrazine with thiosemicarbazide. Using the same procedure, N, N-dimethylthiosemicarbazones were synthesized from acetylpyrazines and N, N-dimethylthiosemicarbazide. A total of 20 compounds (16 novel) were chemically characterized and then tested for antifungal effects on eight strains of fungi and also for antitumor activity against SK-N-MC neuroepithelioma cells. The most effective compound identified in terms of both antifungal and antitumor activity was N, N-dimethyl-2-(1-pyrazin-2-ylethylidene)hydrazinecarbothioamide (5a). The mechanism of action of this and its related thiosemicarbazones was due, at least in part, to its ability to act as a tridentate ligand that binds metal ions. This was deduced from preparation of the related thiosemicarbazones [acetophenone thiosemicarbazone (6) and acetophenone N, N-dimethylthiosemicarbazone (7)] that do not possess a coordinating ring-N, which plays a vital role in metal ion chelation. Furthermore, 5a and several other thiosemicarbazones that showed high antiproliferative activity were demonstrated to have marked iron (Fe) chelation efficacy. In fact, these agents were highly effective at mobilizing (59)Fe from prelabeled SK-N-MC cells and preventing (59)Fe uptake from the serum Fe transport protein, transferrin. In contrast, compounds 6 and 7 that do not possess a tridentate metal-binding site showed little activity. Further studies examining ascorbate oxidation demonstrated that the Fe complexes of the most effective compounds were redox-inactive. Thus, in contrast to other thiosemicarbazones with potent antiproliferative activity, Fe chelation and mobilization rather than free radical generation played a significant role in the cytotoxic effects of the current ligands.

Substituted N-phenylpyrazine-2-carboxamides, their synthesis and evaluation as herbicides and abiotic elicitors

The condensation of substituted pyrazine-2-carboxylic acid chlorides with ring-substituted anilines yielded five substituted pyrazine-2-carboxylic acid amides. Thesynthesis, and analytical, lipophilicity and biological data of the newly synthesizedcompounds are presented in this paper. The photosynthesis inhibition, antialgal activityand the effect of a series of pyrazine derivatives as abiotic elicitors on the accumulation offlavonoids in a callus culture of Ononis arvensis (L.) were investigated. The most activeinhibitor of the oxygen evolution rate in spinach chloroplasts was 6-chloro-pyrazine-2-carboxylic acid (3-iodo-4-methylphenyl)-amide (2, IC(50) = 51.0 micromol.L(-1)). The highestreduction of chlorophyll content in Chlorella vulgaris was found for 5-tert-butyl-N-(4-chloro-3-methylphenyl)-pyrazine-2-carboxamide (3, IC(50) = 44.0 micromol.L(-1)). The maximalflavonoid production (about 900%) was reached after a twelve-hour elicitation processwith 6-chloropyrazine-2-carboxylic acid (3-iodo-4-methylphenyl)-amide (2).

Synthesis and antimycobacterial evaluation of substituted pyrazinecarboxamides

Unsubstituted, halogenated and/or alkylated pyrazine-2-carboxylic acid amides connected via -CONH- bridge with substituted anilines were synthesized using currently known synthetic pathways. The synthetic approach, analytical, spectroscopic, lipophilicity and biological data of 20 newly synthesized compounds are presented. Structure-activity relationships among the chemical structures, the antimycobacterial, antifungal, photosynthesis inhibiting and antialgal activity of the evaluated substituted N-phenylpyrazine-2-carboxamides are discussed. 5-tert-Butyl-6-chloro-N-(3-trifluoromethylphenyl)pyrazine-2-carboxamide (19) has shown the highest activity against Mycobacterium tuberculosis H(37)Rv (MIC=3.13 microg/mL). The highest antifungal effect against Trichophyton mentagrophytes, the most susceptible fungal strain tested, was found for N-(3-trifluoromethylphenyl)pyrazine-2-carboxamide (14, MIC=62.5 micromol/mL). The highest reduction of chlorophyll content in Chlorella vulgaris was found for pyrazine-2-carboxylic acid (3-trifluoromethylphenyl)amide (9, IC(50)=12.1 micromol/L).

A new modification of anti-tubercular active molecules

The connection of two active molecules across an easily released bridge as a new type of potentially active molecule has been studied. The synthesis is based on derivatives that originate from isonicotinoyl hydrazide, pyrazinamide, p-aminosalicylic acid (PAS), ethambutol, and ciprofloxacin. The lipophilicity, hydrolysis (stability of the compounds), and antituberculotic activity as well as the structure-lipophilicity and structure-activity relationships are discussed.

Salicylanilide acetates: synthesis and antibacterial evaluation

A new series of salicylanilide acetates was synthesized and evaluated for their in vitro antifungal and antituberculotic activity. Some of the evaluated compounds possessed comparable or better antifungal activity than a fluconazole standard. All these compounds exhibited very good potential and their in vitro activity against drug resistant and sensitive clinical isolates of Mycobacteria were found to be equivalent or better than a standard of isoniazide, a well-known first-line drug for tuberculosis treatment.

Synthesis and antimicrobial evaluation of new 2-substituted 5,7-di-tert-butylbenzoxazoles

Various synthetic pathways of the 30 novel 2-substituted 5,7-di-tert-butylbenzoxazoles as new potential antimicrobial drugs are discussed. The 28 intermediates are described as well. The compounds were characterized by 1H and 13C NMR spectra, MS spectra, IR/UV spectra and by means of CHN analysis. The purity of the final compounds was checked by HPLC and their lipophilicity (log K) was also determined by means of RP-HPLC. In the present study, the correlation between RP-HPLC retention parameter log K (the logarithm of capacity factor K) and various calculated log P data is shown. The target compounds were tested for their in vitro antimycobacterial activity. Several compounds showed antituberculotic activity comparable with or higher than the standard isoniazide. In vitro cytotoxicity testing of the most active benzoxazoles and isoniazide as a reference drug was performed using MTT assay and compared with isoniazide as a reference drug. Structure-activity relationships among the chemical structures, the physical properties and the biological activities of the evaluated compounds are discussed in the article.