Preparation of pyridopyrazines through tandem Pd-catalyzed C-N/C-C coupling reactions of Ugi adducts

A Pd-catalyzed selective tandem cyclization of the Ugi adduct via Buchwald-Hartwig/C-H bond functionalization reactions has been reported. This sequence offers an interesting approach for synthesizing a wide range of pyrido[1,2-a]pyrazine-3,6-dione scaffolds under mild reaction conditions in moderate to excellent yields. The scope and limitations of the protocol are discussed.

Refining S-acylation: Structure, regulation, dynamics, and therapeutic implications

With a limited number of genes, cells achieve remarkable diversity. This is to a large extent achieved by chemical posttranslational modifications of proteins. Amongst these are the lipid modifications that have the unique ability to confer hydrophobicity. The last decade has revealed that lipid modifications of proteins are extremely frequent and affect a great variety of cellular pathways and physiological processes. This is particularly true for S-acylation, the only reversible lipid modification. The enzymes involved in S-acylation and deacylation are only starting to be understood, and the list of proteins that undergo this modification is ever-increasing. We will describe the state of knowledge on the enzymes that regulate S-acylation, from their structure to their regulation, how S-acylation influences target proteins, and finally will offer a perspective on how alterations in the balance between S-acylation and deacylation may contribute to disease.

Meldrum-Based-1H-1,2,3-Triazoles as Antidiabetic Agents: Synthesis, In Vitro α-Glucosidase Inhibition Activity, Molecular Docking Studies, and In Silico Approach

A series of novel alkyl derivatives (2-5a,b) and 1H-1,2,3-triazole analogues (7a-k) of Meldrum's acid were synthesized in a highly effective way by using "click" chemistry and screened for in vitro α-glucosidase inhibitory activity to examine their antidiabetic potential. ¹H NMR, ¹³C-NMR, and high-resolution electrospray ionization mass spectra (HR-ESI-MS) were used to analyze each of the newly synthesized compounds. Interestingly, these compounds demonstrated high to moderate α-glucosidase inhibitory potency having an IC₅₀ range of 4.63-80.21 μM. Among these derivatives, compound 7i showed extraordinary inhibitory activity and was discovered to be several times more potent than the parent compound Meldrum (1) and the standard drug acarbose. Later, molecular docking was performed to understand the binding mode and the binding strength of all the compounds with the target enzyme, which revealed that all compounds are well fitted in the active site of α-glucosidase. To further ascertain the structure of compounds, suitable X-ray single crystals of compounds 5a, 7a, and 7h were developed and studied. The current investigation has shown that combining 1H-1,2,3-triazole with the Meldrum moiety is beneficial. Furthermore, this is the first time that the aforementioned activity of these compounds has been reported.

Discovery of New Boswellic Acid Hybrid 1H-1,2,3-Triazoles for Diabetic Management: In Vitro and In Silico Studies

A series of 24 new 1H-1,2,3-triazole hybrids of 3-O-acetyl-11-keto-β-boswellic acid (β-AKBA (1)) and 11-keto-β-boswellic acid (β-KBA (2)) was designed and synthesized by employing "click" chemistry in a highly efficient manner. The 1,3-dipolar cycloaddition reaction between β-AKBA-propargyl ester intermediate 3 or β-KBA-propargyl ester intermediate 4 with substituted aromatic azides 5a-5k in the presence of copper iodide (CuI) and Hünig's base furnished the desired products-1H-1,2,3-triazole hybrids of β-AKBA (6a-6k) and β-KBA (7a-7k)-in high yields. All new synthesized compounds were characterized by ¹H-, ¹³C-NMR spectroscopy, and HR-ESI-MS spectrometry. Furthermore, their α-glucosidase-inhibitory activity was evaluated in vitro. Interestingly, the results obtained from the α-glucosidase-inhibitory assay revealed that all the synthesized derivatives are highly potent inhibitors, with IC₅₀ values ranging from 0.22 to 5.32 µM. Among all the compounds, 6f, 7h, 6j, 6h, 6g, 6c, 6k, 7g, and 7k exhibited exceptional inhibitory potency and were found to be several times more potent than the parent compounds 1 and 2, as well as standard acarbose. Kinetic studies of compounds 6g and 7h exhibited competitive and mixed types of inhibition, with ki values of 0.84 ± 0.007 and 1.18 ± 0.0012 µM, respectively. Molecular docking was carried out to investigate the binding modes of these compounds with α-glucosidase. The molecular docking interactions indicated that that all compounds are well fitted in the active site of α-glucosidase, where His280, Gln279, Asp215, His351, Arg442, and Arg315 mainly stabilize the binding of these compounds. The current study demonstrates the usefulness of incorporating a 1H-1,2,3-triazole moiety into the medicinally fascinating boswellic acids skeleton.

ER-Golgi-localized proteins TMED2 and TMED10 control the formation of plasma membrane lipid nanodomains

To promote infections, pathogens exploit host cell machineries such as structural elements of the plasma membrane. Studying these interactions and identifying molecular players are ideal for gaining insights into the fundamental biology of the host cell. Here, we used the anthrax toxin to screen a library of 1,500 regulatory, cell-surface, and membrane trafficking genes for their involvement in the intoxication process. We found that endoplasmic reticulum (ER)-Golgi-localized proteins TMED2 and TMED10 are required for toxin oligomerization at the plasma membrane of human cells, an essential step dependent on localization to cholesterol-rich lipid nanodomains. Biochemical, morphological, and mechanistic analyses showed that TMED2 and TMED10 are essential components of a supercomplex that operates the exchange of both cholesterol and ceramides at ER-Golgi membrane contact sites. Overall, this study of anthrax intoxication led to the discovery that lipid compositional remodeling at ER-Golgi interfaces fully controls the formation of functional membrane nanodomains at the cell surface.

Selective anti-cancer activity against melanoma cells using 3-O-acetyl-β-boswellic acid-loaded 3D-Printed scaffold

This study aimed to develop a local 3 D-printed bioactive graft using poly-caprolacton (PCL) as a drug carrier and 3-O-acetyl-β-boswellic acid (β-ABA) as an anticancer compound. β-ABA-loaded 3 D-printed scaffold was fabricated and physically characterized. The results indicated more desirable mechanical and physical properties of the β-ABA-loaded PCL mat in comparison with the PCL scaffold. Following sustained release of β-ABA, the β-ABA-loaded PCL scaffold revealed selective cytotoxic activity against melanoma cells, while the PCL + ABA with the bolus delivery of β-ABA was toxic against fibroblast cells. Followed by the induction of apoptosis in melanoma cells at the gene level, the result of the western blot showed that the β-ABA-loaded scaffold significantly up-regulated P53 and down-regulated BCL2, with an increment in the ratio of Bax/BCL2. The selective anti-cancer properties of β-ABA-loaded 3 D printed scaffold against melanoma cells indicated that this scaffold could be potentially used as a bioactive graft to improve the melanoma treatment.

Phenoxy pendant isatins as potent α-glucosidase inhibitors: reciprocal carbonyl⋯carbonyl interactions, antiparallel π⋯π stacking driven solid state self-assembly and biological evaluation

Carbonyl–carbonyl (CO⋯CO) interactions are recently explored noncovalent interactions of significant interest owing to their role in the stability of biomacromolecules. Currently, substantial efforts are being made to understand the nature of these interactions. In this study, twelve phenoxy pendant isatins 1–12 have been evaluated for their α-glucosidase inhibitory potential in addition to the analysis of X-ray single crystals of 4 and 9. Both compounds 4 and 9 showed intriguing and unique self-assembled structures. The CO⋯CO and antiparallel displaced π⋯π stacking interactions are mainly involved in the formation of 1D-stair like supramolecular chains of 4 whereas antiparallel π⋯π stacking interactions drive the formation of 1D-columnar stacks of 9. These compounds not only highlight the potential of the isatin moiety in forming strong CO⋯CO and antiparallel π⋯π stacking interactions but also are interesting models to provide considerable insight into the nature of these interactions. The in vitro biological studies revealed that all twelve phenoxy pendant isatins 1–12 are highly potent inhibitors of α-glucosidase enzyme with IC₅₀ values ranging from 5.32 ± 0.17 to 150.13 ± 0.62 μM, showing many fold more potent activity than the standard drug, acarbose (IC₅₀ = 873.34 ± 1.67). Easy access and high α-glucosidase inhibition potential of these phenoxy pendant isatins 1–12 provide an attractive platform for finding more effective medication for controlling postprandial hyperglycemia.

Carbonyl–carbonyl (CO⋯CO) interactions are recently explored noncovalent interactions of significant interest owing to their role in the stability of biomacromolecules.

Synthesis and antimicrobial activity of 1H-1,2,3-triazole and carboxylate analogues of metronidazole

Herein, a series of novel 1H-1,2,3-triazole and carboxylate derivatives of metronidazole (5a-i and 7a-e) were synthesized and evaluated for their antimicrobial activity in vitro. All the newly synthesized compounds were characterized by ¹H NMR, ¹³C NMR, HRMS, and ¹⁹F NMR (5b, 5c and 5h) spectroscopy wherever applicable. The structures of compounds 3, 5c and 7b were unambiguously confirmed by single crystal X-ray analysis diffraction method. Single crystal X-ray structure analysis supported the formation of the metronidazole derivatives. The antimicrobial (antifungal and antibacterial) activity of the prepared compounds was studied. All compounds (except 2 and 3) showed a potent inhibition rate of fungal growth as compared to control and metronidazole. The synthetic compounds also showed higher bacterial growth inhibiting effects compared to the activity of the parent compound. Amongst the tested compounds 5b, 5c, 5e, 7b and 7e displayed excellent potent antimicrobial activity. The current study has demonstrated the usefulness of the 1H-1,2,3-triazole moiety in the metronidazole skeleton.

Palmitoylated acyl protein thioesterase APT2 deforms membranes to extract substrate acyl chains

Many biochemical reactions require controlled recruitment of proteins to membranes. This is largely regulated by posttranslational modifications. A frequent one is S-acylation, which consists of the addition of acyl chains and can be reversed by poorly understood acyl protein thioesterases (APTs). Using a panel of computational and experimental approaches, we dissect the mode of action of the major cellular thioesterase APT2 (LYPLA2). We show that soluble APT2 is vulnerable to proteasomal degradation, from which membrane binding protects it. Interaction with membranes requires three consecutive steps: electrostatic attraction, insertion of a hydrophobic loop and S-acylation by the palmitoyltransferases ZDHHC3 or ZDHHC7. Once bound, APT2 is predicted to deform the lipid bilayer to extract the acyl chain bound to its substrate and capture it in a hydrophobic pocket to allow hydrolysis. This molecular understanding of APT2 paves the way to understand the dynamics of APT2-mediated deacylation of substrates throughout the endomembrane system.

A competitive nature-derived multilayered scaffold based on chitosan and alginate, for full-thickness wound healing

The aim of this study was to evaluate a bioactive multilayer wound dressing, based on chitosan and alginate. To enhance healing potential, Dracaena Cinnabari and Aloe Vera were loaded as separate layers into the scaffold. The bare and bioactive multilayered scaffolds were fabricated by an iterative layering freeze-drying technique. Following of topographical, chemical, and physical assessment, the performance of the scaffolds was evaluated in vitro and in vivo. The results revealed adequate attachment, and proliferation of human foreskin fibroblasts, indicating excellent biocompatibility of the bioactive scaffold. In vivo, the performance of the multi-layered scaffold loaded with the bioactive materials was comparable with Comfeel plus®. The wounds treated with the bioactive scaffold exhibited superior hypergranulation, fibroblast maturation, epithelization, and collagen deposition, with minimal inflammation, and crust formation. It is concluded that the synergism of extracellular matrix-mimicking multi-layered scaffolding with Aloe Vera and Dracaena Cinnabari could be considered as a supportive wound dressing.

Therapeutic potential of N4-substituted thiosemicarbazones as new urease inhibitors: Biochemical and in silico approach

Urease enzyme plays a key role in pathogenesis of gastritis and peptic ulcers. Its inhibition averts our bodies from many disorders including formation of urinary calculi. In agriculture, the high urease content causes severe environmental and hence economic problems. Due to deficiency of effective and safer drugs to tackle the aforementioned disorders, the quest for new scaffolds becomes mandatory in the field of medicinal chemistry. In this regard, we herein report a new series of N⁴-substituted thiosemicarbazones 3a-v as potential candidates for urease inhibition. These new N⁴-substituted thiosemicarbazones 3a-v of distant chemical scaffolds were characterized by advanced spectroscopic techniques, such as FTIR, ¹HNMR, ¹³CNMR, ESI-MS and in the case of compound 3g by single crystal X-ray analysis. The compounds were evaluated for their urease inhibitory potential. All newly synthesized compounds showed significant urease inhibitions with IC₅₀ values in range of 2.7 ± 0.320-109.2 ± 3.217 μM. Molecular docking studies were used for interactions pattern and structure-activity relationship for all compounds, which demonstrated excellent binding interactions with the active site residues, such as hydrogen bonding, π-π interactions, π-H and nickel atom coordination.

Alkali complexes of non-steroidal anti-inflammatory drugs inhibit lung and oral cancers in vitro

Alkali metal complexes (Li, K, and Cs) displayed excellent activities against oral and lung cancer cells with the least toxicity toward normal cells.

Synthesis of Spiro-β-lactam-pyrroloquinolines as Fused Heterocyclic Scaffolds through Post-transformation Reactions

A sequential post-transformation of Ugi four-component reaction/nucleophilic substitution was developed for the synthesis of spiro-β-lactam-pyrroloquinolines. This method involves the Ugi-4CR of 2-chloro-3-formyl quinolines 1a-h, amines 2a-d, 2-chloroacetic acid 3, and isocyanides 4a, 4b for the synthesis of versatile precursors 5a-v. The Ugi adducts were intramolecularly cyclized under basic conditions through the sequential nucleophilic aromatic substitution (S_NAr)/second-order nucleophilic substitution (S_N2) reaction to give spiro-β-lactam-pyrroloquinoline scaffolds 6a-t. This approach is an efficient method for the synthesis of fused bioactive heterocyclic backbones containing quinoline, pyrrolidone, and β-lactam with high bond-forming efficiency.

Heterogeneous Pd/C-catalyzed, ligand free Suzuki-Miyaura coupling reaction furnishes new p-terphenyl derivatives

A series of new para-terphenyls derivatives have been efficiently synthesized by a ligand-free heterogeneous Pd/C-catalyzed two-fold Suzuki-Miyaura coupling reaction. Methyl 5-bromo-2-iodobenzoate was selected to react with a variety of different aryl boronic acids (2a-i). Nine new p-terphenyl derivatives (3a-i) were prepared and the structures were confirmed by several analytical techniques including infrared, spectroscopy, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and in the case of compound 3 b, by X-ray diffraction method. The new derivatives were obtained in very good yields (78-91%). This synthetic facile route is envisioned to improve the preparation of p-terphenyl-based natural products.

A highly green approach towards aromatic nitro group substitutions: catalyst free reactions of nitroimidazoles with carbon nucleophiles in water

We have successfully developed a flexible green aqueous approach for the formation of a carbon–carbon bond by the reaction of highly-enolizable carbanions (mostly derived from 1,3-dicarbonyl compounds) with an aromatic carbon bearing a nitro group. The key step involves a nucleophilic displacement reaction. All newly synthesized compounds were unambiguously characterized via various spectroscopic techniques including NMR, mass spectrometry and single-crystal X-ray diffraction as applicable. We believe that our study will be useful in providing new insights into catalyst-free water-mediated nucleophilic substitution reactions.

We have successfully developed a flexible green aqueous approach for the formation of a carbon–carbon bond by the reaction of highly-enolizable carbanions (mostly derived from 1,3-dicarbonyl compounds) with an aromatic carbon bearing a nitro group.

Complexes of N- and O-Donor Ligands as Potential Urease Inhibitors

We report five new transition-metal complexes that inhibit the urease enzyme. Barbituric acid (BTA), thiobarbituric acid (TBA), isoniazid (INZ), and nicotinamide (NCA) ligands were employed in complexation reactions. The resulting complexes were characterized using a variety of analytical techniques including infra-red and UV-vis spectroscopy, ¹H NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. We describe two mononuclear complexes with a general formula {[M(NCA)₂(H₂O)₄](BTA)₂(H₂O)}, where M = Co (1) and Zn (2), a mononuclear complex {[Ni(NCA)₂(H₂O)₄](TBA)₂(H₂O)} (3), and two polymeric chains of a general formula {[M(INZ) (H₂O)₃](BTA)₂(H₂O)₃}, where M = Co (4) and Zn (5). These complexes displayed significant urease enzyme inhibition with IC₅₀ values in the range of 3.9-19.9 μM.

Synthesis of 3-Oxoisoindoline-1-carboxamides through Sequential Four-Component Ugi Reaction/Oxidative Nucleophilic Substitution of Hydrogen

This paper describes a diversity-oriented approach to the formation of 3-oxoisoindoline-1-carboxamide derivatives utilizing the potential of the nitro group as a directing group. The reaction proceeds through a novel class of post-transformation reactions through a sequential four-component Ugi reaction/oxidative nucleophilic substitution of hydrogen. The 3-oxoisoindoline-1-carboxamide derivatives were synthesized in the presence of a base under mild reaction conditions with high regio- and chemoselectivity. The aerobic oxidation, high bond-forming efficiency, high atom economy, and good to excellent yields are the main advantages of this approach.

Sodium, Potassium, and Lithium Complexes of Phenanthroline and Diclofenac: First Report on Anticancer Studies

Diclofenac or 2-[(2',6'-dichlorophenyl)amino]phenyl}acetic acid (dcf) is a nonsteroidal anti-inflammatory drug, and 1,10-phenanthroline (phen) is a well-known enzyme inhibitor. In this study, three new alkali metal complexes (1-3) containing both phen and dcf were prepared, and their structures were characterized by a variety of analytical techniques including infrared and UV-vis spectroscopy, 1H NMR and 13C NMR elemental analysis, mass spectrometry, and single-crystal X-ray diffraction analysis. In these complexes, phen binds via a N,N'-chelate pocket, while the monoanionic dcf-ligand remains either uncoordinated (in the case of 1 and 3) or coordinated in a bidentate fashion (in the case of 2). All three complexes crystallize in the triclinic space group P-1. [Na2(phen)2 (H2O)4][dcf]2 (1) is a dinuclear sodium complex, where two crystallographically identical Na+ cations adopt a distorted five-coordinate spherical square-pyramidal geometry, with a [N2O3] donor set. [K2(phen)2(dcf)2(H2O)4] (2) is also a dinuclear complex where the crystallographically unique K+ cation adopts a distorted seven-coordinate geometry comprising a [N2O5] donor set. [Li(phen)(H2O)2][dcf] (3) is a mononuclear lithium complex where the Li+ cation adopts a four-coordinate distorted tetrahedral geometry comprising a [N2O2] donor set. The complexes were evaluated for their anticancer activity against lung and oral cancer cell lines as well as for their antibacterial potential. The prepared complexes displayed very good antibacterial and anticancer activities with an excellent bioavailability.

Regio- and chemo-selective cyclization of allenic-Ugi products for the synthesis of 3-pyrroline skeletons

A highly efficient and stable novel class of allenic-Ugi products through a Crabbé homologation reaction is successfully demonstrated. Then, a regio- and chemo-selective cyclization of allenic-Ugi derivatives in a 5-exo-dig fashion to access 3-pyrroline skeletons is developed. Also, computational studies were performed and explained to provide insights into the reaction mechanism. This approach displays high bond-forming efficiency and atom economy with high yields.

Crystal structure, shape analysis and bioactivity of new LiI, NaI and MgII complexes with 1,10-phenanthroline and 2-(3,4-dichlorophenyl)acetic acid

Reactions of 1,10-phenanthroline (phen) and 2-(3,4-dichlorophenyl)acetic acid (dcaH) with Mn (CO3) (M = LiI, NaI and MgII; n = 1 and 2) in MeOH yield the mononuclear lithium complex aqua[2-(3,4-dichlorophenyl)acetato-κO](1,10-phenanthroline-κ2 N,N′)lithium(I), [Li(C8H5Cl2O2)(C12H8N2)(H2O)] or [Li(dca)(phen)(H2O)] (1), the dinuclear sodium complex di-μ-aqua-bis{[2-(3,4-dichlorophenyl)acetato-κO](1,10-phenanthroline-κ2 N,N′)sodium(I)}, [Na2(C8H5Cl2O2)2(C12H8N2)2(H2O)2] or [Na2(dca)2(phen)2(H2O)2] (2), and the one-dimensional chain magnesium complex catena-poly[[[diaqua(1,10-phenanthroline-κ2 N,N′)magnesium]-μ-2-(3,4-dichlorophenyl)acetato-κ2 O:O′] 2-(3,4-dichlorophenyl)acetate monohydrate], {[Mg(C8H5Cl2O2)(C12H8N2)(H2O)2](C8H5Cl2O2)·H2O} n or {[Mg(dca)(phen)(H2O)2](dca)·H2O} n (3). In these complexes, phen binds via an N,N′-chelate pocket, while the deprotonated dca− ligands coordinate either in a monodentate (in 1 and 2) or bidentate (in 3) fashion. The remaining coordination sites around the metal ions are occupied by water molecules in all three complexes. Complex 1 crystallizes in the triclinic space group P\overline{1} with one molecule in the asymmetric unit. The Li+ ion adopts a four-coordinated distorted seesaw geometry comprising an [N2O2] donor set. Complex 2 crystallizes in the triclinic space group P\overline{1} with half a molecule in the asymmetric unit, in which the Na+ ion adopts a five-coordinated distorted spherical square-pyramidal geometry, with an [N2O3] donor set. Complex 3 crystallizes in the orthorhombic space group P212121, with one Mg2+ ion, one phen ligand, two dca− ligands and three water molecules in the asymmetric unit. Both dcaH ligands are deprotonated, however, one dca− anion is not coordinated, whereas the second dca− anion coordinates in a bidentate fashion bridging two Mg2+ ions, resulting in a one-dimensional chain structure for 3. The Mg2+ ion adopts a distorted octahedral geometry, with an [N2O4] donor set. Complexes 1–3 were evaluated against urease and α-glucosidase enzymes for their inhibition potential and were found to be inactive.

Slow magnetic relaxation in Dy2 and Dy4 complexes of a versatile, trifunctional polydentate N,O-ligand

A binuclear Dy^III complex exhibits slow relaxation of magnetization under an applied dc field, while its tetranuclear counterpart exhibits “true” zero-field SMM behaviour.

A new nitrogen rich open chain diazine ligand system: synthesis coordination chemistry and magneto-structural studies

The synthesis and coordination chemistry of a new series of open chain diazine based ligands (L3aH₂, L3bH₂, and L3cH₂) is reported. The ligands comprise a central disubstituted bipyridine moiety with two bridging alkoxide oxygen donors, together with diazine and pyridine terminal groups strategically located to coordinate three metal centres. Reactions of L3aH₂ and L3bH₂ with CuX₂ (X^- = ClO₄, Cl, NO₃) yield a trinuclear complex (1) and 1-D copper chains (2, 3). In these complexes the ligands bind copper ions via N_bipyridne, trans N_diazine, O_hydrazone, and N_pyridne donors while vacant sites are occupied by counter ions or solvent molecules (methanol, water, acetonitrile). Reaction of L3cH₂ with MnCl₂ affords a linear trinuclear Mn complex (4), where the Mn(ii) ions are connected via μ₂-O_hydrazone linkers with no N-N bridging. Reaction of L3aH₂ with Fe(SO₃CF₃)₂ yields a tetranuclear mixed valence Fe complex (5), in which both trans N-N and O_hydrazone bridging is observed. Magnetic studies reveal the presence of moderate to strong antiferromagnetic interactions in complexes 1-4 while a mix of ferromagnetic and antiferromagnetic interactions is observed in complex 5.

A novel bis-1,2,4-benzothiadiazine pincer ligand: synthesis, characterization and first row transition metal complexes

The synthesis and coordination chemistry of ligand LH₂ to first row transition metals is described in which it acts as a tridentate N,N′,N′′-donor.

Synthesis, characterization and magnetic studies on mono-, di-, and tri-nuclear Cu(ii) complexes of a new versatile diazine ligand

The synthesis and coordination chemistry of a new open-chain diazine ligand (L4H₂) containing bipyridine, oxime and hydrazone functionalities is reported. Reaction of L4H₂ with CuCl₂·2H₂O affords the mononuclear complex [Cu(L4H₂)Cl₂] (1) in which the ligand acts as a neutral tridentate N,N',N'' donor, whereas treatment with a large excess of CuCl₂·2H₂O affords the dinuclear complex [Cu₂(L4H)Cl₃(CH₃OH)(H₂O)] (2) in which the ligand is singly-deprotonated at the diazine, offering N,N',N'' and N,N' donor sets to two Cu(ii) ions. Reaction with Cu(NO₃)₂·3H₂O yields the trinuclear complex, [Cu₃(L4H)₂(CH₃OH)₄(NO₃)₄] (3) in which the ligand is again singly deprotonated, but now presents a tetradentate N,N',N'',N'''-donor set to the first Cu(ii) and behaves as an N,O-chelate to a second Cu(ii), with a conformational change from cis to trans at the diazine moiety. When the latter reaction is repeated in the presence of a mild base, a second trinuclear complex is isolated, [Cu₃(L4)₂(CH₃CH₂OH)](NO₃)₂ (4) in which both the diazine and oxime functionalities of the ligand are deprotonated which subsequently bridges all three Cu(ii) ions, acting as an N,N',N'' donor to the first Cu(ii), a N,N' donor to a second Cu(ii) (similar to 2) and as a terminal O-donor to a third Cu(ii) ion. The Cu(ii) ions are linked mutually cis via the two-atom diazine bridge in the case of 2 and 4 and trans in the case of 3. Magnetic studies reveal the presence of weak ferromagnetic interactions in 2 (g = 2.2, J/k = +12.8 K) and strong antiferromagnetic interactions in both 3 and 4 (g = 2.093 J/k = -140 K and g = 2.24 J/k = -300 K respectively).

Copper-promoted aerial oxidation of benzothiadiazines: access to benzothiadiazine S-oxide heterocycles

Cu(II)-promoted aerial oxidation of a series of benzothiadiazines () under ambient conditions affords the first structurally characterised examples of thiadiazine S-oxides (). The isolation of the homoleptic Cu(II) 3-(2'-pyridyl)benzothiadiazide-S-oxide complex provides insight into the reaction mechanism.

Complexes of ditopic carbo- and thio-carbohydrazone ligands--mononuclear, 1D chain, dinuclear and tetranuclear examples

Ligands based on carbo- and thio-carbohydrazone cores, modified with pyridine, carboxylate and oxime ends, have been examined. They display a tautomeric versatility based on the flexible nature of the hydrazone linkages, leading to varied coordination motifs. Examples of mononuclear (Co(II), Ni(II)), dinuclear (Co(III)), 1D chain (Cu(II)) and square [2 × 2] grid (Ni(II)) complexes are obtained. Ferromagnetic (Cu(II)) and antiferromagnetic (Ni(II)) exchange is observed, with spin coupling in the Ni(II)(4) square grids propagated through the μ-O and μ-S bridges. Weak antiferromagnetic exchange (J = -6.0 cm(-1)) is observed for the μ-O bridged grid, despite the large Ni-O-Ni angles (137-141°), while for the μ-S bridged grids much stronger exchange is observed (J = -148 cm(-1), -198 cm(-1)). This is much larger than expected based on the Ni-S-Ni bridge angles (151-169°), and is associated with the soft (less polarizing than oxygen) nature of the sulfur bridge, which would allow for much more efficient transmission of spin exchange than observed in the μ-O bridged case. Structures and variable temperature magnetic data are included, and spin exchange is analyzed using normal Heisenberg exchange models. No examples involving oxime (NO) bridging are reported, which reflects the positioning of the N,O and N,S donor combinations in each ligand, and the preferred coordination through these donor atoms.