In the present work, we report a detailed investigation of four supramolecular coordination complexes, Zn(Quino)(2)(CH3OH)(2) 2, Zn(QUino)(2)H2O3, Mn(Quino)(2) (CH3OH)(2) 4 and Ca(Quino)(2)(CH3OH)(2) 5, obtained from the self-assembling of Zn(II), Mn(11) and Ca(11) acceptors with the N-phenyl-4-hydroxyquinoline ligand donor QuinoH 1, possessing the beta,beta'-diketonate moiety. The structure of the supramolecular arrangement of the isolated complexes have been investigated by single crystal X-ray crystallography. The synthetic N-phenyl quinolone-linker that forms a pi-pi stacking supramolecular synthon with the coordination preferences of metal ions has been used to construct coordination driven self-assembled "metallosupramolecular" architectures. [GRAPHICS] .

A novel two step methodology for readily accessible natural “pulvinone” derivatives in excellent yields has been developed starting from activated precursors, bearing a functionalized 1,3-dioxolane-2,4-diones (OCA’s), as dually protected-activated synthons of α-hydroxy acids. The present procedure is based on a tandem C-acylation-cyclization process under mild conditions with good yields. Additionally, pulvinones show an important medicinal profile with the tetronate heterocycle exhibiting favorable pharmacokinetic (PK) and ADME-Tox properties that can be considered unexploited so far due to synthetic limitations.

The synthesis and biological evaluation of 5-arylidene-N-acetyl-tetramic acids cadmium(II) complexes are reported. Eleven novel compounds were prepared, characterized by nuclear magnetic resonance experiments and screened for their antimicrobial activity against five bacterial species (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus [MRSA]) and two fungi (Candida albicans and Cryptococcus neoformans). The complexes showed similar or enhanced activities against MRSA in comparison to the corresponding ligands and, additionally, promising antifungal activities against C. neoformans. The most active compounds 3c and 3h showed remarkable activities against MRSA (minimum inhibitory activity [MIC] values of 32 and 4 μg/ml, respectively) and C. neoformans (MIC values of 8 and 16 μg/ml, respectively), accompanied by no human cell toxicity and hemolytic activity within the tested concentration range. The results demonstrate that appropriately functionalized tetramic acids attached with lipophilic alkanoyl chain and after complexation with cadmium(II) ions may act as valuable lead compounds for further investigations toward the development of novel antibacterial and/or antifungal agents.

The steady rise of the antimicrobial resistance is a major global threat to human health that requires the urgent need for novel antibiotics. In this work we report the synthesis of a small library of 3-subsituted-5-arylidene tetramic acids in order to investigate the scope of our previously established methodology via an intermediate oxazolone and their antimicrobial activity. From this series of 14 tetramic acids, 11 derivatives are novel and one of them is a Schiff base, which was structurally characterized with single-crystal X-ray analysis and NMR spectroscopy. The compounds incorporating a lipophilic acyl group at carbon-3 of the ring showed moderate to high activity with minimum inhibitory activity of 4-32 mu g/mL against methicillin-resistant Staphylococcus aureus (MRSA), accompanied by no human cell toxicity and hemolytic activity within the tested concentration range. The substituent at para position of the aryl ring seemed to have no or little effect on the antimicrobial activity of these compounds.

This study aims at the further expansion of knowledge on the antimicrobial activities of the tetramic acid moiety and the effect of metal complexation. Complexes of the N-acetyl-3-acetyl-5-benzylidenetetramic acid with Mn, Co, Ni, Cu, Zn and Cd were synthesized and screened against 5 key ESKAPE pathogens (Escherichia coli, methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa) and 2 fungi (Cryptococcus neoformans and Candida albicans). The cadmium complex was found to effectively inhibit the fungus Cryptococcus neoformans with minimum inhibitory concentration (MIC) of 8 μg/mL, with no human cell toxicity and hemolytic activity within the tested concentration range. The biologically active tetramic acid‑cadmium complex was structurally characterized by single-crystal X-ray analysis. Furthermore, the thermal stability of the ligand and the complexes was investigated along with NMR and EPR studies of the Cd(II) and Co(II) complexes respectively.

Carbonyl compounds are of paramount importance in the formation of C-C bonds and metal-ion control of their reactivity offers a way to promote, inhibit, or control such reactions [1]. The coordination of the oxygen atom of a carbonyl compound to a metal center is likely to modify the reactivity of that group. Products formally derived by attack at the carbonyl group may arise either by direct attack at the carbon atom or by attack at the metal followed by attack at carbon by the coordinated nucleophile. There has been a debate over the relative importance of these two competing mechanisms in biological and biomimetic systems. These two mechanisms may well both be operative in some cases. The principal reactions of carbonyl compounds are of two types: The first type is that in which the nucleophile reacts with the electrophilic carbon atom of a carbonyl group to generate a new tetrahedral center (Figure 1). The Carbonyl Groups as Scaffolds in Coordination Chemistry

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

In this work we present a structural and spectroscopic analysis of a copper(II) N-acetyl-5-arylidene tetramic acid by using both experimental and computational techniques. The crystal structure of the Cu(II) complex was determined by single crystal X-ray diffraction and shows that the copper ion lies on a centre of symmetry, with each ligand ion coordinated to two copper ions, forming a 2D sheet. Moreover, the EPR spectroscopic properties of the Cu(II) tetramic acid complex were also explored and discussed. Finally, a computational approach was performed in order to obtain a detailed and precise insight of product structures and properties. It is hoped that this study can enrich the field of functional supramolecular systems, giving place to the formation of coordination-driven self-assembly architectures.

In this work we describe the synthesis and characterization of two supramolecular coordination complexes, namely [Zn(Cuma)2(MeOH)2] 2 and [Mn(Cuma)2(MeOH)2] 3, obtained from the self-assembly of Zn(II) and Mn(II) acceptors with the 3-benzoyl-4-hydroxycoumarin ligand donor (1) possessing the β,β′-diketonate moiety. The coordination mode of the ligand, incorporating intra- and intermolecular hydrogen bonds with the metal atoms, was established by single crystal X-ray diffraction. The Zn(II) and Mn(II) complexes each show a 1D structural motif which is further assembled into 3D supramolecular architecture by hydrogen bonds and π-stacking interactions.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

AbstractUtilization of optically active α‐hydroxy acids allows for the enantiocontrolled preparation of tetronic acids.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A new strategy for the synthesis of tetronic acids with control over the regioselective introduction of substituents at the C-5 position has been developed. The construction of the densely functionalized quaternary carbon center within these molecules is of great importance. The key element for the proposed protocol was the utilization of O-carboxyanhydrides (OCA's) of optically active α-hydroxy acids, as promising bidentate protective/activating precursors. The structure of the new compounds was investigated by using NMR spectral data and X-ray structural analyses.

A new route to N-acetyl-3-acyl-5-arylidenetetramic acids was developed and applied to the synthesis of a small library of compounds with diversity at carbon 3 of the heterocyclic ring. The 3-acetyl derivative was used as ligand for complexation with zinc(II) and copper(II) acetates. Both the ligand and the zinc complex were studied by X-ray single crystal structure analysis, the zinc complex forms ribbons by H-bonding from the ethanol to a neighbouring molecule.

A series of coumarin and quinolinone-3-aminoamide derivatives was synthesized and evaluated for its potency in inhibition of cancer cell growth. The structure of N -[2-(dimethylamino) ethyl]-4-hydroxy-2-oxo-1-phenyl-1,2-dihydroquinoline-3-carboxamide was unambiguously confirmed by X-ray diffraction analysis, which revealed the cis conformation of the amide bond resulting from the presence of two intramolecular hydrogen bonds. Graphical Abstract

Title compounds (III) are synthesized in high yields (no values given for (IIIa)) and evaluated for cytostatic activities against various cancer cell lines.

Coumarins, quinolinones, tetramic and tetronic acid analogues, play an integral role in biological systems and forms a variety of complexes with environmentally active metals. A survey of their synthesis as ligands and their ability to form coordination compounds is presented.