Recent advances in the synthesis of piperazine based ligands and metal complexes and their applications

A survey of isatin hybrids and their biological properties

The emergence of diverse infections worldwide, which is a serious global threat to human existence, necessitates the urgent development of novel therapeutic candidates that can combat these diseases with efficacy. Molecular hybridization has been established as an efficient technique in designing bioactive molecules capable of fighting infections. Isatin, a core nucleus of an array of compounds with diverse biological properties can be modified at different positions leading to the creation of novel drug targets, is an active area of medicinal chemistry. This review containing published articles from 2005 to 2022 highlights isatin hybrids which have been synthesized and reported in the literature alongside a discussion on their biological properties. The enriched structure-activity relationship studies discussed provides insights for the rational design of novel isatin hybrids with tailored biological properties as effective therapeutic candidates inspired by nature.

The medicinal chemistry of piperazines: A review

The versatile basic structure of piperazine allows for the development and production of newer bioactive molecules that can be used to treat a wide range of diseases. Piperazine derivatives are unique and can easily be modified for the desired pharmacological activity. The two opposing nitrogen atoms in a six-membered piperazine ring offer a large polar surface area, relative structural rigidity, and more acceptors and donors of hydrogen bonds. These properties frequently result in greater water solubility, oral bioavailability, and ADME characteristics, as well as improved target affinity and specificity. Various synthetic protocols have been reported for piperazine and its derivatives. In this review, we focused on recently published synthetic protocols for the synthesis of the piperazine and its derivatives. The structure-activity relationship concerning different biological activities of various piperazine-containing drugs has also been highlighted to provide a good understanding to researchers for future research on piperazines.

Nano-assembly of cytotoxic amides of moronic and morolic acid

Moronic acid and morolic acid, less frequently studied plant triterpenoids, were subjected to derivation with several structural modifiers, namely, piperazine-, pyrazine-, 1H-indole- and L-methionine-based compounds. Derivation was targeted to design and prepare novel compounds capable of nano-assembling and/or displaying cytotoxicity. Formation of nanostructures has been proven for several novel target compounds that formed different types of nanostructures, either in chloroform or in water. Isometric nanoparticles with broad size distributions (12 and 25), distorted single sheets (23) or very large thin warped films (13) were formed in chloroform solutions. Sheet-like nanostructures (12 and 23), and sphere-like nanostructures (hydrogen bonding connected nanoparticles; 3, 5, 13, 21 and 25) were formed in water suspensions. Cytotoxicity was also investigated and compared with that of the parent triterpenoids, showing enhanced effect of 18 that was the most successful derivative of the prepared series with sufficient balance between its cytotoxicity in CEM (IC50 = 11.7 ± 2.4 μM), HeLa (IC50 = 9.0 ± 0.7 μM) and G-361 (IC50 = 10.6 ± 5.5 μM) cancer cell lines, and toxicity in BJ (IC50 = 43.3 ± 1.5 μM). The calculated selectivity index values for 18 are SI = 3.9 (CEM), 4.8 (HeLa) and 4.4 (G-361). Additional compounds displaying cytotoxicity were 5, 7, 9 and 15, all of them showed comparable cytotoxicity with 18, in the investigated cancer cell lines; however, they were more toxic in BJ than 18.

Hydrazylpyridine salicylaldehyde-copper(II)-1,10-phenanthroline complexes as potential anticancer agents: synthesis, characterization and anticancer evaluation

We synthesized and analyzed nine unique copper(II) hydrazylpyridine salicylaldehyde and 1,10-phenanthroline complexes, [Cu(L1a)(phen)] (Cugdupt1), [Cu(L2a)(phen)]·(CH3CN) (Cugdupt2), [Cu(L3a)(phen)] (Cugdupt3), [Cu(L4a)(phen)]·(CH3CN) (Cugdupt4), [Cu(L5a)(phen)] (Cugdupt5), [Cu(L6a)(phen)] (Cugdupt6), [Cu(L7a)(phen)] (Cugdupt7) [Cu(L8a)(phen)] (Cugdupt8) and [Cu(L9a)(phen)]·0.5(H2O) (Cugdupt9). We were motivated by the intriguing properties of the coupled ligands of hydrazylpyridine, salicylaldehyde, and 1,10-phenanthroline. The MTT assay demonstrated that Cugdupt1-Cugdupt9 have higher anticancer activity than L1H2-L9H2, phen and cisplatin on A549/DDP cancer cells (A549cis). Cugdupt1-Cugdupt9 were superior to cisplatin with IC50 values of 1.6-100.0 fold on A549cis cells (IC50(Cugdupt1-Cugdupt9) = 0.5-30.5 μM, IC50(cisplatin) = 61.5 ± 1.0 μM). However, Cugdupt1-Cugdupt9 had lower cytotoxicity toward the HL-7702 normal cells. Cugdupt1 and Cugdupt8 can induce reduction of mitochondrial respiratory chain complexes I/IV (MRCC-I/IV), mitophagy pathways, and eventually protein regulation and adenosine triphosphate (ATP) depletion in A549cis cells. The findings indicated that Cugdupt1 and Cugdupt8 caused cell death via both ATP diminution and mitophagy pathways. Finally, Cugdupt8 demonstrated high efficacy and no obvious cytotoxicity in A549 tumor-bearing mice. This study thus helps evaluate the potential of the hydrazylpyridine salicylaldehyde-copper(II)-1,10-phenanthroline compounds for cisplatin-resistant tumor therapy.

Building Up a Piperazine Ring from a Primary Amino Group via Catalytic Reductive Cyclization of Dioximes

Piperazine is one of the most frequently found scaffolds in small-molecule FDA-approved drugs. In this study, a general approach to the synthesis of piperazines bearing substituents at carbon and nitrogen atoms utilizing primary amines and nitrosoalkenes as synthons was developed. The method relies on sequential double Michael addition of nitrosoalkenes to amines to give bis(oximinoalkyl)amines, followed by stereoselective catalytic reductive cyclization of the oxime groups. The method that we developed allows a straightforward structural modification of bioactive molecules (e.g., α-amino acids) by the conversion of a primary amino group into a piperazine ring.

Direct C(3)5-H Polyfluoroarylation of 2-Amino/alkoxy Pyridines Enabled by a Transient and Electron-deficient Palladium Intermediate

Herein, we present an unprecedented azine-limited C5-H polyfluoroarylation of 2-aminopyridines enabled by a transient and electron-deficient perfluoroaryl-Pd species via C-H/C-H coupling. The protocol further allows C3(5)-H polyfluoroarylation of 2-alkoxypyridines guided by sterics and electronics for the first time. The late-stage C-H functionalization of drugs, drug derivatives, and natural product derivatives and synthesis of C5-aryl drug derivatives further demonstrated the method's utility. The preliminary mechanistic studies reveal that the synergistic combination of the bulky yet electrophilic perfluoroaryl-Pd species and the partial nucleophilicity of the C5-position of 2-amino/alkoxy-pyridines is the origin of reactivity and selectivity. Importantly, the first experimental evidence for the role of diisopropyl sulfide is provided.

Synthesis and anticancer mechanisms of zinc(II)-8-hydroxyquinoline complexes with 1,10-phenanthroline ancillary ligands

Twenty new zinc(II) complexes with 8-hydroxyquinoline (H-Q1-H-Q6) in the presence of 1,10-phenanthroline derivatives (D1-D10) were synthesized and formulated as [Zn(Q1)₂(D1)] (DQ1), [Zn(Q2)₂(D2)]·CH₃OH (DQ2), [Zn(Q1)₂(D3)] (DQ3), [Zn(Q1)₂(D4)] (DQ4), [Zn(Q3)₂(D5)] (DQ5), [Zn(Q3)₂(D4)] (DQ6), [Zn(Q4)₂(D5)]·CH₃OH (DQ7), [Zn(Q4)₂(D6)] (DQ8), [Zn(Q4)₂(D3)]·CH₃OH (DQ9), [Zn(Q4)₂(D1)]·H₂O (DQ10), [Zn(Q5)₂(D4)] (DQ11), [Zn(Q6)₂(D6)]·CH₃OH (DQ12), [Zn(Q5)₂(D2)]·5CH₃OH·H₂O (DQ13), [Zn(Q5)₂(D7)]·CH₃OH (DQ14), [Zn(Q5)₂(D8)]·CH₂Cl₂ (DQ15), [Zn(Q5)₂(D9)] (DQ16), [Zn(Q5)₂(D1)] (DQ17), [Zn(Q5)₂(D5)] (DQ18), [Zn(Q5)₂(D10)]·CH₂Cl₂ (DQ19) and [Zn(Q5)₂(D3)] (DQ20). They were characterized using multiple techniques. The cytotoxicity of DQ1-DQ20 was screened using human cisplatin-resistant SK-OV-3/DDP ovarian cancer (SK-OV-3CR) cells and normal hepatocyte (HL-7702) cells. Complex DQ6 showed low IC₅₀ values (2.25 ± 0.13 μM) on SK-OV-3CR cells, more than 3.0-8.0 times more cytotoxic than DQ1-DQ5 and DQ7-DQ20 (≥6.78 μM), and even 22.2 times more cytotoxic than the standard cisplatin, the corresponding free H-Q1-H-Q6 and D1-D10 alone (>50 μM). As a comparison, DQ1-DQ20 displayed nontoxic rates against healthy HL-7702 cells. Furthermore, DQ6 and DQ11 induced significant apoptosis via mitophagy pathways. DQ6 also significantly inhibited tumor growth in an in vivo SK-OV-3-xenograft model (ca. 49.7%). Thus, DQ6 may serve as a lead complex for the discovery of new antitumor agents.

Construction and Chlorine Resistance of Thiophene-Poly(ethyleneimine)-Based Dual-Functional Nanofiltration Membranes

The demand to improve the chlorine resistance of polyamide (PA) membranes is escalated with greater amounts of chlorine-containing disinfectant being used in global water treatment during the COVID-19 pandemic. In this work, we designed thiophene-functionalized poly(ethyleneimine) (TPEI) materials first and grafted them onto a conventional PA membrane to develop novel nanofiltration membranes (PEI-M, TPEI-1-M, TPEI-2-M). These membranes have dual-functionalized selective surfaces covered by hydrophilic amino groups and electron-rich thiophene moieties, which endow these membranes with superior chlorine resistance and improved separation performance. The modified membranes increase the rejection of MgCl2 from 86.5% of the nascent PA membrane (PA-M) to higher than 93.0% without sacrificing the membrane water permeability. More stable separation performance is achieved with all of the as-prepared membranes than PA-M after exposure to a 2000 ppm sodium hypochlorite solution. TPEI-2-M outperforms other membranes after being treated in a chlorination intensity of 16,000 ppm·h with the smallest flux loss and the highest MgCl2 rejection. This is mainly ascribed to the highest amount of amino and thiophene moieties on the TPEI-2-M surface. This study provides an effective protocol for developing novel PA-based nanofiltration membranes while demonstrating its superiority over current technologies with exceptional separation performance and antichlorine ability.

A novel biocompatible Eu-based coordination polymers of cytarabine anticancer drug: Preparation, luminescence properties and in vitro anticancer activity studies

In this study, we use cytarabine anticancer drug to synthesize a new rare earth complex with Europium ion. The study work is an attempt to investigate luminescence and biological properties of the Eu-based coordination polymers of cytarabine (Eu-CP-Ara) anticancer drug which have been prepared by us. Eu-CP-Ara has luminescence properties with emission centering at about 619 nm excited with 394 nm. We study cytarabine and Eu-CP-Ara in vitro cytotoxicity. Cytotoxicity of Eu-CP-Ara against lung cancer cells (A549) could even be comparable to the inhibitory effect of cytarabine ligands, showing the advantage of antitumor activity. In addition, Eu-CP-Ara showed lower cytotoxicity to normal liver cells (L02). At the same, from the CLSM images, Eu-CP-Ara has successfully entered the A549 cell. Hence, Eu-CP-Ara can be used as a potential anticancer drug. Eu-CP-Ara may be an effective strategy for the tracking cytarabine against tumours and might impart better accurate treatment effect and therapeutic efficiency.

Design, synthesis, and fungicidal activity of novel N-substituted piperazine-containing phenylpyridines against cucumber downy mildew

BACKGROUND

Cucumber downy mildew (CDM) is a severe plant disease and affects the yield of cucumber production worldwide. As the resistance toward conventional fungicides is emerging as a ubiquitous issue, it is urgent to discover efficient fungicides with unique structures.

RESULTS

In this study, a series of novel phenylpyridine derivatives were designed and synthesized. Bioassays revealed that most of these compounds possessed excellent fungicidal activities against CDM. Among the phenylpyridine compounds, 2-(4-(4-(tert-butyl)benzyl)piperazin-1-yl)-6-phenylnicotinonitrile (C8) [half-maximal effective concentration (EC₅₀ ) = 4.40 mg L^-1 ] displayed the highest activity, which was better than those of the commercial fungicides, such as azoxystrobin (EC₅₀  = 42.77 mg L^-1 ) and flumorph (EC₅₀  = 41.94 mg L^-1 ). Furthermore, the molecular electrostatic potential of high-activity compound C8 indicated that nitrogen atom of the cyano group on the pyridine ring was in the negative region and may easily form hydrogen bonds and allow for electrostatic interactions with potential receptors.

CONCLUSIONS

This study demonstrated that the novel N-substituted piperazine-containing phenylpyridine derivatives could be further developed as a candidate compound to control CDM.

Structure-activity relationship of three new piperazine derivates with anxiolytic-like and antidepressant-like effects

Anxiety and depression are common mental disorders affecting millions of people worldwide. Unsatisfactory clinical outcomes with the use of the available pharmacological interventions among some patients demand newer drugs with proven efficacy, safety, and tolerability profile. In this study, the LQFM211, LQFM213, and LQFM214 were designed from the piperazine scaffold and administered orally in mice. These mice were later evaluated in the open field, elevated plus maze, and forced swimming tests to assess the exploratory, anxiolytic, and antidepressant-like activities, respectively. The mechanism of action of these new derivatives was evaluated using Flumazenil (benzodiazepine antagonist) and WAY100635 (5-HT1A receptor antagonist). Unlike LQFM214, the LQFM211 and LQFM213 elicited anxiolytic and antidepressant-like effects. The blockade of the effect of LQFM213 by WAY100635 suggests the involvement of the serotonergic pathway. Keywords: anxiety, behavioral pharmacology, depression, medicinal chemistry.

Cancer-Targeted Chitosan-Biotin-Conjugated Mesoporous Silica Nanoparticles as Carriers of Zinc Complexes to Achieve Enhanced Chemotherapy In Vitro and In Vivo

Despite being the most common component of numerous metalloenzymes in the human body, zinc complexes are still under-rated as chemotherapeutic agents. Herein, the present study opens up a key route toward enhanced chemotherapy with the help of two Zn^II complexes (ZnMBC) synthesized alongside Mannich base ligands to upsurge biological potency. Further, well-established mesoporous silica nanoparticles (MSNs) have been chosen as carriers of the titled metallodrugs in order to achieve anticancer drug delivery. A pH-sensitive additive, namely, chitosan (CTS) conjugated with biotin is tagged to MSNs for the targeted release of core agents inside tumors selectively. In general, CTS blocks ZnMBC inside the mesopores of MSNs, and biotin acts as a targeting ligand to improve tumor-specific cellular uptake. CTS-biotin surface decoration significantly enhanced the cellular uptake of ZnMBC through endocytosis. A panel of four human cancer cell lines has revealed that ZnMBC (1/2)@MSNs-CTS-biotin nanoparticles (NPs) exhibits unprecedented enhanced cytotoxicity toward cancer cells with IC₅₀ values ranging from 6.5 to 28.8 μM through induction of apoptosis. NPs also possess great selectivity between normal and cancer cells despite this potency. Two-photon-excited in vitro imaging of normal (HEK) and cancer (HeLa) cells has been performed to confirm the biased drug delivery. Also, NP-induced apoptosis was found to be dependent on targeting DNA and ROS generation. Moreover, a lower range of LD₅₀ values (153.6-335.5 μM) were observed upon treatment zebrafish embryos with NPs in vivo. Because of the anatomical similarity to the human heart, the heart rate of NP-treated zebrafish has been analyzed in assessing the cardiac functions, which is in favor of the early clinical trials of ZnMBC (1/2)@MSNs-CTS-biotin candidates for their further evaluation as a chemotherapeutic and chemopreventive agent toward human cancers, especially adenocarcinoma.

Oxidative DNA cleavage mediated by a new unexpected [Pd(BAPP)][PdCl4] complex (BAPP = 1,4-bis(3-aminopropyl)piperazine): crystal structure, DNA binding and cytotoxic behavior

A novel Pd(ii) double complex, [Pd(BAPP)][PdCl₄], containing the 1,4-bis(3-aminopropyl)piperazine (BAPP) ligand is investigated. X-ray crystallography of a single crystal confirmed the structure of the [Pd(BAPP)][PdCl₄] complex. The spectroscopic behavior was also elucidated using elemental analysis, nuclear magnetic resonance and Fourier-transform infrared spectroscopy, and mass spectrometry. The antimicrobial susceptibility of the [Pd(BAPP)][PdCl₄] complex against all tested microbial strains was lower than that of the BAPP ligand except for C. albicans. The cytotoxic impacts of the BAPP ligand and its [Pd(BAPP)][PdCl₄] complex were evaluated in vitro for HepG2, CaCo-2 and MCF7 cell lines as well as the WI-38 normal cell line. The anticancer activity was markedly improved by the complexation. The [Pd(BAPP)][PdCl₄] complex could selectively inhibit the tested cancer cells in a safe way to the non-tumorigenic cell (WI-38). From the DNA binding studies with ultraviolet-visible spectrophotometry, the [Pd(BAPP)][PdCl₄] complex interacts more efficiently with the calf thymus DNA than its BAPP ligand through the intercalative binding mode. In the absence of an external reductant, the [Pd(BAPP)][PdCl₄] complex cleaved the intact supercoiled pBR322 DNA under physiological conditions in a concentration-dependent manner. Additionally, electrophoretic experiments were performed in the presence of different radical scavengers, namely DMSO, NaN₃ and KI, and ruled out the hydrolytic mechanistic pathway of the reaction and suggested that the oxidative mechanism is the preferred one. The results of the binding affinity of the [Pd(BAPP)][PdCl₄] complex to human DNA were modeled using a molecular docking study showing that the complex interacts more strongly with human DNA than the ligand. Finally, an in vitro pharmacokinetic study was assessed through in silico ADME predictions.

Piperazine-1,4-diol (PipzDiol): synthesis, stereodynamics and assembly of supramolecular hydrogen-bonded 2D networks

The manuscript describes a novel small building block, 1,4-piperazinediol (PipzDiol), which has an extended H-bond donor structure compared to piperazine.

Investigation of the influence of chirality and halogen atoms on the anticancer activity of enantiopure palladium(ii) complexes derived from chiral amino-alcohol Schiff bases and 2-picolylamine

In order to evaluate the impact of chirality and halogen-substitution pattern on biological activity, four mixed-ligand enantiomeric pairs of Pd(ii) complexes were synthesized and characterized.