In this study, three new organic ligands N'-(benzylidene)-6-chloropyrazine-2-carbohydrazonamide (L₁), 6-chloro-N'-(4-nitrobenzylidene)picolinohydrazonamide(L₂), and N'-(benzylidene)-4-chloropicolinohydrazonamide (L₃) and three copper coordination compounds (Cu(L₁)Cl₂, Cu(L₂)Cl₂ and Cu(L₃)Cl₂) based on them were synthesized. All obtained compounds were characterized using appropriate analytical techniques: elemental analysis (EA), thermogravimetric analysis (TG-DTG), Fourier transform infrared spectroscopy (FTIR) and flame-atomic absorption spectrometry (F-AAS). These methods of physicochemical analyses helped to assume that the complexation in three cases proceeds in a bidentate manner. The X-ray investigation confirmed the synthesis pathway and molecular structures for L₁ and L₃ ligands. The antimicrobial activity of the obtained compounds was then comprehensively investigated, where Cu(L₃)Cl₂ showed the strongest antibacterial properties against all tested bacteria (Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli). LN229 human glioma cells and BJ human normal fibroblasts cells were treated with tested compounds and their cytotoxicity was evaluated with MTT test. The effect of complexing on antitumor activity has been investigated. The ligand L₁ and its complex showed similar activity against normal cells while complexation increases toxicity against cancer cells in concentrations of 50 and 100 μM. For the one pair of ligand/complex compounds the apoptosis detection, cell cycle analysis and gene expression analysis (qRT-PCR) were performed. Cu(L₁)Cl₂ showed the stronger toxic effect in comparison with L₁ due to the population of early apoptotic cells which revealed metabolic activity in MTT assay.

In this study, six new 2,6-disubstituted thiosemicarbazone derivatives of pyridine were synthesized (4–9), and their tuberculostatic activity was evaluated. All of them showed two- to eightfold higher activity (minimum inhibitory concentration (MIC) 0.5–4 µg/mL) against the resistant strain compared with the reference drug. Compounds 5 and 7, which contained the most basic substituents—pyrrolidine and piperidine—in their structure, strongly inhibited the growth of the standard strain (MIC 2 µg/mL). Furthermore, the same derivatives exhibited activity comparable to that of the reference drugs against some types of Gram-positive bacteria (MIC 0.49 µg/mL) and showed no cytotoxicity (IC50 > 50 µg/mL) in HaCaT cells. The zwitterionic structure of each compound was determined using X-ray crystallography. Absorption, distribution, metabolism, and excretion analyses showed that all compounds are good drug candidates. Thus, compounds 5 and 7 were identified as leading structures for further research on antituberculosis drugs with extended effects.

Three new 4-phenylpicolin derivatives with a thiosemicarbazone structure were synthesized and evaluated for tuberculostatic activity. The compounds were obtained by the condensation of methyl 4-phenylpicolonimidate with the corresponding cycloalkylamino-1-carbothiohydrazides. The ¹H NMR temperature spectra obtained showed proton lability at the nitrogen atom N2, and X-ray crystallography confirmed the zwitterionic structure of all products. ADME calculations indicate that the compounds can be tested as future drugs. All compounds were absorbed in the gastrointestinal tract. All compounds also showed very good tuberculostatic activity (MIC 3.1–12.5 µg/mL). Derivative 1b showed the best selectivity for M. tuberculosis compared to the other pathogenic species tested. The study has allowed the emergence of imine derivative 1b as a good structure for further optimization in the search for antitubercular drugs.

Four novel methyl 4-phenylpicolinoimidate derivatives of hydrazone have been synthesized and evaluated for their antimicrobial activity, including tuberculostatic activity. The compounds obtained are condensates of hydrazonamide or hydrazide with 5-nitro-2-furaldehyde or 5-nitro-2-thiophenecarboxaldehyde. The antimicrobial activity of the tested compounds varied. Compound 3b exhibited significant activity against the tested Gram-positive bacteria (7.8–250 µg/mL). The results of structural tests revealed that the compound is the only one obtained in the form of a Z isomer. Tuberculostatic activity tests showed higher activity of derivatives 3a and 4a containing nitrofuran systems (MICs 3.1–12.5 µg/mL). This research allowed us to identify hydrazone 3b as a starting point for further optimization in the search for antimicrobial drugs. Likewise, compound 4a appears to be a good guiding structure for use in future research on new anti-tuberculosis drugs.

To investigate how structural modifications affect tuberculostatic potency, we synthesized seven new piperidinothiosemicrabazone derivatives 8–14, in which three of them had a pyrazine ring replacing the pyridine ring. Derivatives 8–9 and 13–14 exhibited significant activity against the standard strain (minimum inhibitory concentration (MIC) 2–4 μg/mL) and even greater activity against the resistant M. tuberculosis strain (MIC 0.5–4 μg/mL). Additionally, the effects of compounds 8–9 were entirely selective (MIC toward other microorganisms ≥ 1000 μg/mL) and non-toxic (IC50 to HaCaT cells 5.8 to >50 μg/mL). The antimycobacterial activity of pyrazine derivatives 11–12 was negligible (MIC 256 to >500 μg/mL), indicating that replacing the aromatic ring was generally not a promising line of research in this case. The zwitterionic structure of compound 11 was determined using X-ray crystallography. Absorption, distribution, metabolism, and excretion (ADME) calculations showed that all compounds, except 11, could be considered for testing as future drugs. An analysis of the structure–activity relationship was carried out, indicating that the higher basicity of the substituent located at the heteroaromatic ring might be of particular importance for the antituberculous activity of the tested groups of compounds.