Synthesis of 2,6-diaryl-substituted pyridines and their antitumor activities

An In-Depth Exploration of Six Decades of the Kröhnke Pyridine Synthesis

The Kröhnke Pyridine Synthesis has been discovered about six decades ago (1961), by Fritz Kröhnke and Wilfried Zecher at the University of Giessen. The original method involved the reaction of α-pyridinium methyl ketone salts with α,β-unsaturated carbonyl compounds in the presence of a nitrogen source, frequently ammonium acetate. Since its discovery, the Kröhnke methodology has been demonstrated to be suitable for the preparation of mono-, di-, tri- and tetra-pyridines, with important applications in several research fields. Over the years, a number of modifications to the original approach have been developed and reported, enabling for the broad applicability of these methods even in modern days, also for the synthesis of non-pyridine compounds. In this critical and tutorial review, we will thoroughly explore and discuss the potential of the original method, the refinements that have been made over the years, as well as some applications arising from each type of pyridine and/or non-pyridine compounds produced by Kröhnke's approach.

Synthesis and biological evaluation of titanium dioxide/thiopolyurethane composite: anticancer and antibacterial effects

Nanocomposites incorporating titanium dioxide (TiO2) have a significant potential for various industrial and medical applications. These nanocomposites exhibit selectivity as antimicrobial and anticancer agents. Antimicrobial activity is crucial for medical uses, including applications in food processing, packaging, and surgical instruments. Additionally, these nanocomposites exhibit selectivity as anticancer agents. A stable nanocomposite as a new anticancer and antibacterial chemical was prepared by coupling titanium dioxide nanoparticles with a polyurethane foam matrix through the thiourea group. The titanium dioxide/thiopolyurethane nanocomposite (TPU/TiO2) was synthesized from low-cost Ilmenite ore and commercial polyurethane foam. EDX analysis was used to determine the elemental composition of the titanium dioxide (TiO2) matrix. TiO2NPs were synthesized and were characterized using TEM, XRD, IR, and UV-Vis spectra. TiO2NPs and TPU foam formed a novel composite. The MTT assay assessed Cisplatin and HepG-2 and MCF-7 cytotoxicity in vitro. Its IC50 values for HepG-2 and MCF-7 were 122.99 ± 4.07 and 201.86 ± 6.82 µg/mL, respectively. The TPU/TiO2 exhibits concentration-dependent cytotoxicity against MCF-7 and HepG-2 cells in vitro. The selective index was measured against both cell lines; it showed its safety against healthy cells. Agar well-diffusion exhibited good inhibition zones against Escherichia coli (12 mm), Bacillus cereus (10 mm), and Aspergillus niger (19 mm). TEM of TPU/TiO2-treated bacteria showed ultrastructure changes, including plasma membrane detachment from the cell wall, which caused lysis and bacterial death. TPU/TiO2 can treat cancer and inhibit microbes in dentures and other items. Also, TPU/TiO2 inhibits E. coli, B. cereus, and A. niger microbial strains.

Silver complexes with substituted terpyridines as promising anticancer metallodrugs and their crystal structure, photoluminescence, and DNA interactions

Six silver hexafluoroantimonate complexes (1-6) with 4'-(4'-substituted-phenyl)-2,2':6',2''-terpyridine compounds bearing hydrogen (L1), methyl (L2), methylsulfonyl (L3), chloro (L4), bromo (L5) and iodo (L6) were prepared and characterized by 1H NMR, 13C NMR, IR, elemental analysis and single crystal X-ray diffraction. All the compounds exhibit interesting photoluminescence properties in the solid state and solution. In vitro data demonstrate that all of them show higher antiproliferative activities than cisplatin against three human carcinoma cell lines, A549, Eca-109 and MCF-7. Compound 3 exhibits the lowest IC50 value (2.298 μM) against A549 cell lines, which is 2.963 μM for 4 against Eca-109 and 1.830 μM for 1 against MCF-7. For silver halogen-substituted terpyridine compounds, their anticancer activities decrease following the sequence of -Cl, -Br, and -I substituents. The comparison results show that their anticancer activity is significantly higher than that of their free ligands. The DNA interaction was studied by fluorescence titration, circular dichroism spectroscopy and molecular modeling methods. Spectrophotometric results reveal that the compounds have strong affinity binding with DNA as intercalators and molecular docking studies indicate that the binding is contributed by the π-π stacking and hydrogen bonds. The DNA binding ability of the complexes has been correlated with their anticancer activities, which could potentially provide a new rationale for the future design of terpyridine-based metal complexes with antitumor potential.

[6-(Thiophen-2-yl)-2,2′-bipyridine]bis(triphenylphosphine) Copper(I) Tetrafluoroborate

The novel heteroleptic copper (I) complex [6-(thiophen-2-yl)-2,2′-bipyridine]bis(triphenylphosphine) copper(I) tetrafluoroborate (1), formulated as [CuL(PPh3)2]BF4, was synthesized in two steps, utilizing the diimine type ligand L = 6-(thiophen-2-yl)-2,2′-bipyridine and triphenylphosphine (PPh3). The compound was characterized both in the solid state and in solution by employing single crystal X-ray diffraction, IR, UV, and NMR spectroscopies. The complex is an orange emitter that demonstrates a photoluminescence quantum yield of 2.6% in the solid state.

A New Concept of Enhancing the Anticancer Activity of Manganese Terpyridine Complex by Oxygen-Containing Substituent Modification

Eleven manganese 4'-substituted-2,2':6',2″-terpyridine complexes (1a-1c and 2a-2h) with three non-oxygen-containing substituents (L^1a-L^1c: phenyl, naphthalen-2-yl and naphthalen-1-yl, L^1a-L^1c) and eight oxygen-containing substituents (L^2a-L^2h: 4-hydroxyl-phenyl, 3-hydroxyl-phenyl, 2-hydroxyl-phenyl, 4-methoxyl-phenyl, 4-carboxyl-phenyl, 4-(methylsulfonyl)phenyl, 4-nitrophenyl and furan-2-yl) were prepared and characterized by IR, elemental analysis or single crystal X-ray diffraction. In vitro data demonstrate that all of these show higher antiproliferative activities than cisplatin against five human carcinoma cell lines: A549, Bel-7402, Eca-109, HeLa and MCF-7. Compound 2d presents the strongest antiproliferative effect against A549 and HeLa cells, with IC₅₀ values being 0.281 μM and 0.356 μM, respectively. The lowest IC₅₀ values against Bel-7402 (0.523 μM) Eca-109 (0.514 μM) and MCF-7 (0.356 μM) were obtained for compounds 2h, 2g and 2c, respectively. Compound 2g with a nitro group showed the best results on the whole, with relevantly low IC₅₀ values against all the tested tumor cells. The DNA interactions with these compounds were studied by circular dichroism spectroscopic and molecular modeling methods. Spectrophotometric results revealed that the compounds have strong affinities in binding with DNA as intercalators, and the binding induces DNA conformational transition. Molecular docking studies indicate that the binding is contributed by the π-π stacking and hydrogen bonds. The anticancer activities of the compounds are correlated with their DNA binding ability, and the modification of oxygen-containing substituents significantly enhanced the anticancer activity, which could provide a new rationale for the future design of terpyridine-based metal complexes with antitumor potential.

Iron-Catalysed [3+3] Annulation of Oxime Acetates and Enaminones towards the Synthesis of Multi-Substituted Pyridines

A direct access to unsymmetrical and symmetrical multi-substituted pyridines has been accomplished via iron-catalysed [3+3] annulation of oxime acetates with enaminones. This protocol is featured by easily available starting materials, no requirement of expensive additives and ligands, operational simplicity, and good tolerance with diverse functional groups.

Synthesis, Molecular Docking Study, and Cytotoxicity Evaluation of Some Novel 1,3,4-Thiadiazole as Well as 1,3-Thiazole Derivatives Bearing a Pyridine Moiety

Pyridine, 1,3,4-thiadiazole, and 1,3-thiazole derivatives have various biological activities, such as antimicrobial, analgesic, anticonvulsant, and antitubercular, as well as other anticipated biological properties, including anticancer activity. The starting 1-(3-cyano-4,6-dimethyl-2-oxopyridin-1(2H)-yl)-3-phenylthiourea (2) was prepared and reacted with various hydrazonoyl halides 3a–h, α-haloketones 5a–d, 3-chloropentane-2,4-dione 7a and ethyl 2-chloro-3-oxobutanoate 7b, which afforded the 3-aryl-5-substituted 1,3,4-thiadiazoles 4a–h, 3-phenyl-4-arylthiazoles 6a–d and the 4-methyl-3- phenyl-5-substituted thiazoles 8a,b, respectively. The structures of the synthesized products were confirmed by spectral data. All of the compounds also showed remarkable anticancer activity against the cell line of human colon carcinoma (HTC-116) as well as hepatocellular carcinoma (HepG-2) compared with the Harmine as a reference under in vitro condition. 1,3,4-Thiadiazole 4h was found to be most promising and an excellent performer against both cancer cell lines (IC₅₀ = 2.03 ± 0.72 and 2.17 ± 0.83 µM, respectively), better than the reference drug (IC₅₀ = 2.40 ± 0.12 and 2.54 ± 0.82 µM, respectively). In order to check the binding modes of the above thiadiazole derivatives, molecular docking studies were performed that established a binding site with EGFR TK.

Pyridine: the scaffolds with significant clinical diversity

The nitrogen-bearing heterocycle pyridine in its several analogous forms occupies an important position as a precious source of clinically useful agents in the field of medicinal chemistry research. This privileged scaffold has been consistently incorporated in a diverse range of drug candidates approved by the FDA (Food and Drug Administration). This moiety has attracted increasing attention from several disease states owing to its ease of parallelization and testing potential pertaining to the chemical space. In the next few years, a larger share of novel pyridine-based drug candidates is expected. This review unifies the current advances in novel pyridine-based molecular frameworks and their unique clinical relevance as reported over the last two decades. It highlights an inclination to the use of pyridine-based molecules in drug crafting and the subsequent emergence of several potent and eligible candidates against a range of diversified diseases.

The nitrogen-bearing heterocycle pyridine in its several analogous forms occupies an important position as a precious source of clinically useful agents in the field of medicinal chemistry research.

Terpyridines as promising antitumor agents: an overview of their discovery and development

INTRODUCTION

The fused aromatic system of terpyridines makes them good, innocent ligands for various metals. The resulting complexes have been extensively studied for both their biological activity and physico-chemical properties. However, although free ligands also have an interesting biological activity, their share in recent research is considerably limited.

AREAS COVERED

This review covers the literature on the anticancer activity of terpyridines with special attention being paid to their use as free ligands. Whenever possible, the mechanism of action has been discussed, thereby providing evidence of the substantial differences between sole ligands or less stable complexes and those that have heavier elements.

EXPERT OPINION

The existing literature indicates that there is a specific attitude for investigating terpyridines and their transition metal complexes. While the latter have been well explored and recognized in the scientific community, the free terpyridines are considered to be useful solely due to their complexing ability. At the same time, terpyridines could have similar or even higher anticancer potency than their complexes. Moreover, a mechanistic analysis of the stability and intracellular activity would provide information that would be useful for designing new drugs.

H2pyhox - Octadentate Bis(pyridyloxine)

A new versatile chelating ligand for intermediate size and softness radiometals [⁶⁴Cu]Cu²⁺ and [¹¹¹In]In³⁺, H₂pyhox, was synthesized by introducing pyridine as a new donor moiety to complement 8-hydroxyquinoline on an ethylenediamine backbone. The combination of pyridine and oxine as donor sets was explored through structural analysis, and crystals of the three metal complexes with Cu²⁺, La³⁺, and In³⁺ demonstrate how the ligand adapts to accommodate metal ions of different sizes and charge. Exhaustive in-batch UV solution studies characterized the protonation constants of the free ligand as well as the formation constants of the metal complexes with Cu²⁺, In³⁺, and La³⁺. Preliminary concentration-dependent radiolabeling studies with [¹¹¹In]In³⁺ and [⁶⁴Cu]Cu²⁺ show the robustness of H₂pyhox to successfully coordinate both radiometals under mild conditions (<15 min, room temperature, pH 6). H₂pyhox is the first oxinate ligand to successfully radiolabel [²²⁵Ac]Ac³⁺, albeit only at high concentrations (0.1-1 mM) with gentle heating to 37 °C. Whole serum, protein, and ligand challenge assays further demonstrate the kinetic inertness of the [¹¹¹In]In³⁺ and [⁶⁴Cu]Cu²⁺ radiometal-ligand complexes, confirming H₂pyhox to be a promising versatile radiopharmaceutical chelator.

Copper chloride complexes with substituted 4'-phenyl-terpyridine ligands: synthesis, characterization, antiproliferative activities and DNA interactions

Eleven copper chloride coordination compounds (1-11) with 4'-(4'-substituted-phenyl)-2,2':6',2''-terpyridine ligands bearing hydrogen (L¹), cyano (L²), p-hydroxyl (L³), m-hydroxyl (L⁴), o-hydroxyl (L⁵), methoxyl (L⁶), iodo (L⁷), bromo (L⁸), chloro (L⁹), fluoro (L¹⁰) or methylsulfonyl (L¹¹) were prepared and characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. Antiproliferative activities against tumor cells were investigated and DNA interactions were studied by circular dichroism spectroscopy and molecular modeling methods. In vitro data demonstrate that all the compounds exhibit higher antiproliferative activities as compared to cisplatin against five human carcinoma cell lines: A549, Bel-7402, Eca-109, HeLa and MCF-7. Compound 6 with methoxyl shows the best anti-proliferation activity. Spectrophotometric results reveal the strong affinity of the compounds for binding with DNA as intercalators and induce DNA conformational transitions. The results of molecular docking studies show that the compounds interact with DNA through π-π stacking, van der Waals forces, hydrophobic interactions and hydrogen bonds. The binding energies between compound 11 and three macromolecules, including DNA duplex, oligonucleotide and DNA-Topo I complex, are the lowest. The binding stability of compounds containing hydroxyl, methoxy and methylsulfonyl groups with biological macromolecules mainly relies on the hydrogen bonds. The ability of a compound to form hydrogen bonds can promote its binding to biological targets, thereby exhibiting high antiproliferative activity.

Synthesis of Novel Pyridine Bearing Biologically Active Imidiazolyl, Pyrazolyl, Oxa/thiadiazolyl and Urea Derivatives as Promising Anticancer Agents

BACKGROUND

A novel series of pyridine containing 1,3,4-oxa/thiadiazol derivatives 4a,b, pyrazole derivatives 5-7, thiazole derivatives 9a,b and 17a-c, urea derivatives 12a-c, imidiazole derivative 16, imidazo[1,2-a]pyridine derivatives 18a, b, tetrazole 19, pyrane 20 and pyridine derivatives 21 has been synthesized.

OBJECTIVE

This research aims to synthesize 6-(Trifluoromethyl)-2-{[3-(trifluoromethyl)phenyl] amino} nicotinohydrazide 2 and 6-(trifluoromethyl)-2-{[3-(trifluoromethyl)phenyl]amino} pyridin-3-carboaldhyde 15 as key intermediate for the synthesis of novel pyridine derivatives bearing different heterocyclic rings in order to study the additive effect of this ring toward tumor cell lines.

METHODS

6-(Trifluoromethyl)-2-{[3-(trifluoromethyl)phenyl]amino} nicotinohydrazide 2 was synthesized in a series of synthetic steps and was used as key intermediate for the synthesis of compounds 3-(1,3,4- oxa/thiadiazol-2-yl)-6-(trifluoromethyl)-N-(3- trifluoromethyl) phenyl) pyridin-2-amine 4a,b, (3,5-dimethyl- 1H-pyrazol-1-yl derivatives) [6-(trifluoromethyl)-2-{[3- trifluoromethyl) phenyl] amino} pyridin-3- yl]methanone 5a,b, 6-8, 9a,b and 12a-c. Also, 6-(trifluoromethyl)-2-{[3-(trifluoromethyl)phenyl]amino} pyridin-3-carboaldhyde (15) was used as a key intermediate for the synthesis of novel series of pyridine derivatives with different heterocyclic ring (16-21).

RESULTS

Structures of the newly synthesized compounds were established by elemental analysis and spectral data. All the synthesized compounds were screened for their in vitro anticancer activity against liver cancer (HepG2), human colon cancer (HT-29) and human breast adenocarcinoma cell lines (MCF-7).

CONCLUSION

All the synthesized compounds were investigated for their in vitro antitumor activity. Compounds 4b, 9a,b and 19 showed higher antitumor activity than the doxorubicin. Interestingly, pyridine with pfluorophenyl urea 12a demonstrated the most potent antitumor activity. The activity of these compounds is strongly dependent on the basic skeleton of the molecules and the nature of the heterocyclic ring attached to the pyridine moiety.

Antiproliferative Activity of Some Newly Synthesized Substituted Pyridine Candidates Using 4-(Aaryl)-6-(naphthalen-1-yl)-2-oxo-1,2-dihydropyridine-3-carbonitrile as Synthon

Herein, we used nicotinonitrile derivatives 4a,b as scaffolds to build novel and active antineoplastic agents. The reaction of nicotinonitrile derivatives 4a,b with POCl3/PCl5 and/or hydrazine hydrate afforded 2-chloropyridones 6a,b and 2-hydrazinyl nicotinonitrile derivatives 11a,b, respectively, as building blocks for various heterocyclic compounds. The structures of all of the synthesized heterocycles were elucidated from their spectral and elemental analyses. The cytotoxic activities of the prepared derivatives were evaluated against different cancer cell lines. Results revealed potential cytotoxic effects of the synthesized compounds against evaluated cell lines, where NCIH 460 and RKOP 27 cell lines were the most affected by the prepared compounds. Derivative 14a was the most effective against all tested cell lines in terms of the obtained IC50 values (25 ± 2.6, 16 ± 2, 127 ± 25, 422 ± 26, and 255 ± 2 nM against NCIH 460, RKOP 27, HeLa, U937, and SKMEL 28 cells, respectively).

Facile synthesis and antiproliferative activity of new 3-cyanopyridines

Background

Pyridines have been reported to possess various pharmacological activities.

Results

Sodium 3-oxo-3-(2-oxo-2H-chromen-3-yl)prop-1-en-1-olate (2) and sodium 3-oxo-3-(3-oxo-3H-benzo[f]chromen-2-yl)prop-1-en-1-olate (7) were prepared and reacted with 2-cyano-N'-(1-aryl(heteryl)ethylidene)acetohydrazides 3a-d to produce 2-oxo-1,2-dihydropyridine-3-carbonitrile derivatives 5a-d and 9a-d, respectively, in good yields. Also, 3a-d reacted with sodium (2-oxocyclopentylidene)methanolate (11a) or sodium (2-oxocyclohexylidene) methanolate (11b) to yield 2-oxo-tetrahydro-1H-cyclopenta[b]pyridine-3-carbonitriles 13a-d and 2-oxo-hexahydroquinoline-3-carbonitriles 13e-h, respectively. The mechanisms that account for the formation of the products are discussed. Additionally, the structures of all the newly synthesized products are confirmed, based on elemental analysis and spectral data. Several of the newly synthesized compounds are evaluated for their antitumor activity against HEPG2 and their structure activity relationship (SAR) was studied.

Conclusions

The results revealed that the pyridine derivatives 5c and 5d (IC₅₀ = 1.46, 7.08 µM, respectively) have promising antitumor activity against liver carcinoma cell line (HEPG2), compared to the reference drug, doxorubicin.

A comprehensive review of topoisomerase inhibitors as anticancer agents in the past decade

The topoisomerase enzymes play an important role in DNA metabolism, and searching for enzyme inhibitors is an important target in the search for new anticancer drugs. Discovery of new anticancer chemotherapeutical capable of inhibiting topoisomerase enzymes is highlighted in anticancer research. Therefore, biologists, organic chemists and medicinal chemists all around the world have been identifying, designing, synthesizing and evaluating a variety of novel bioactive molecules targeting topoisomerase. This review summarizes types of topoisomerase inhibitors in the past decade, and divides them into nine classes by structural characteristics, including N-heterocycles compounds, quinone derivatives, flavonoids derivatives, coumarin derivatives, lignan derivatives, polyphenol derivatives, diterpenes derivatives, fatty acids derivatives, and metal complexes. Then we discussed the application prospect and development of these anticancer compounds, as well as concluded parts of their structural-activity relationships. We believe this review would be invaluable in helping to further search potential topoisomerase inhibition as antitumor agent in clinical usage.

Novel Nicotinonitrile Derivatives Bearing Imino Moieties Enhance Apoptosis and Inhibit Tyrosine Kinase

Background:

Fused heterocyclic containing pyrazolopyridine systems have several medicinal activities including cytotoxic and carcinostatic activities.

Objective:

To investigate the antiproliferative activity and associated mechanism(s) of a novel series of nicotinonitrile derivatives.

Method:

The series has been synthesized by the reaction of hydrazonoyl chlorides with each of 4-(4- methoxyphenyl)-3-methyl-6-oxo-6,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile and 2-amino-4-(4- methoxyphenyl)-6,7-dihydro-5H-cyclopenta[b]pyridine-3-carbonitrile in dioxane in basic medium. The assigned structures for each of the new products were identified via elemental and spectral data. Moreover, the cytotoxic activity for some selected products was screened.

Results:

Derivatives 5g, 7i, 8 and 9 had their IC50 at ~ 1-3 µM and derivatives 7b, 7d, and 7f were similar to 5- fluorouracil and had their IC50 at ~ 5 µM against breast (MCF-7) and colon (HCT-116) cell lines. All derivatives were specific in action and safe to normal fibroblasts (WI38). Only derivative 9 caused some toxicity but at high concentration of 93 µM. These derivatives exerted strong antiproliferative activity through inducing intrinsic apoptosis as indicated from the significant induction of caspases 9 and 3 by 3-6 folds in colon cells and/or inhibiting tyrosine kinase (TK) and hence arresting the cell cycle.

Conclusion:

Compounds 8 and 5g were the most potent anticancer agents inhibiting the TK by 86 and 89% and their IC50 of the enzyme were 311 and 352 nM, respectively. We believe that these derivatives deserve further investigation and these chemical moieties could offer promising anticancer drugs.

Synthesis, characterization, DNA binding, topoisomerase I inhibition and antiproliferation activities of three new functionalized terpyridine platinum(II) complexes

Three new platinum(II) complexes with pendent morpholine were synthesized, namely complex 1 ([Pt(L)Cl]CF₃SO₃), complex 2 ([Pt(L)(NH₃)](CF₃SO₃)₂) and complex 3 ([Pt(L)(PPh₃)](CF₃SO₃)₂), where L = 4'-[4-(4-morpholinobutyloxy)phenyl]-2,2':6',2″-terpyridine and PPh₃ = triphenylphosphine. The detailed molecular structures of complex 3, L and its precursor L' (1,4'-[4-(4-bromobutyloxy)phenyl]-2,2':6',2″-terpyridine) were determined by single crystal X-ray diffraction. An evaluation of in vitro cytotoxicity for both ligand and complexes was performed by methyl thiazolyl tetrazolium (MTT) assay in three cancer cell lines and normal cells as the control, respectively. IC₅₀ values of complexes 1-3 were lower than those exhibited for the reference drug cisplatin, and selectivity of these complexes were greater than cisplatin. Among them, complex 3 with a leaving group PPh₃ was found to be the most efficacious complex against certain cell lines, especially for cisplatin-resistant A549cisR cells. These complexes were found to bind DNA, induce efficient DNA unwinding. Meanwhile, topoisomerase (Topo) I inhibitory activities by three complexes were detected, and a minimum inhibitory concentration of 15 μM of complex 3 was found totally inhibit Topo I activity.

An efficient and ecofriendly synthesis of highly functionalized pyridones via a one-pot three-component reaction

A simple and convenient protocol has been developed for the synthesis of N-amino-3-cyano-2-pyridone derivatives by a one-pot reaction of cyanoacetohydrazide, activated nitrile substrates (malononitrile, ethyl cyanoacetate, cyanoacetamide) and aromatic aldehydes in the presence of piperidine in water or a mixture of water and ethanol. The sequence of cascade reactions includes Knoevenagel condensation, Michael addition, intramolecular cyclization, imine-enamine tautomerization and oxidative aromatization. The main advantages of this procedure are availability of starting compounds, simple procedure, mild conditions, easy purification of products and the use of water or water/ethanol as green solvents.

In-vitro antitumor activity of new quaternary phosphonium salts, derivatives of 3-hydroxypyridine

This work presents the results of in-vitro biological activity studies of three novel anticancer agents, phosphonium salts based on the 3-hydroxypyridine scaffold, including one derivative of 4-deoxypyridoxine. Proliferation and viability of cells treated with these compounds was assessed by the colony formation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Effects of the compounds on apoptosis and cell cycle were studied by flow cytometry using annexin V-FITC/propidium iodide and propidium iodide staining, respectively. The influence of the compounds on mitochondrial membrane potential and intracellular reactive oxygen species was evaluated using tetramethyl rhodamine ethyl and DCFHA staining. Western blot analysis was used to study the changes in the expression of Bcl-xL, Bax, and caspase-3 apoptotic proteins. The treatment of ovarian adenocarcinoma cells OVCAR-4 with the tested compounds inhibited the growth and induced cell cycle arrest in the G1 phase. 3-Hydroxypyridine derivatives induced apoptosis by hyperexpression of Bax and caspase-3, whereas 4-deoxypyridoxine derivative induced cell death partly by reactive oxygen species generation and caspase-3 hyperexpression. These results indicate that the quaternary phosphonium salts studied represent potential therapeutic agents for the treatment of ovarian cancer.

Synthesis of functionalised fluorinated pyridine derivatives by site-selective Suzuki-Miyaura cross-coupling reactions of halogenated pyridines

The Suzuki-Miyaura reaction of 2,6-dichloro-3-(trifluoromethyl)pyridine with 1 equiv of arylboronic acids resulted in site-selective formation of 2-aryl-6-chloro-3-(trifluoromethyl)pyridine. Due to electronic reasons, the reaction takes place at the sterically more hindered position. The selectivity was rationalised by DFT calculations. The one-pot reaction with two different arylboronic acids afforded 2,6-diaryl-3-(trifluoromethyl)pyridine containing two different aryl substituents. The reactions proceeded smoothly in the absence of phosphine ligands. In addition, Suzuki-Miyaura reactions of 2,6-dichloro-4-(trifluoromethyl)pyridine with one or two equivalents of arylboronic acids were carried out.