Synthesis of the A–D Ring System of the Gambieric Acids

The A–D fragment of gambieric acids A and C has been synthesized using an asymmetric Tsuji–Trost allylation reaction to couple the two key segments. The A ring fragment has been prepared by a short and highly efficient route involving diastereoselective Lewis acid mediated alkylation of an acetal. Iterative ring-closing metathesis reactions have been used to construct cyclic ethers and assemble the tricyclic B–D fragment

Tuning Proton Disorder in 3,5-Dinitrobenzoic Acid Dimers: the Effect of Local Environment

The carboxylic acid dimer is a frequently observed intermolecular association used in crystal engineering and design, which can show proton disorder across its hydrogen bonds. Proton disorder in benzoic acid dimers is a dynamic, temperature-dependent process whose reported occurrence is still relatively rare. A combination of variable temperature X-ray and neutron diffraction has been applied to demonstrate the effect of local crystalline environment on both the degree and onset of proton disorder in 3,5-dinitrobenzoic acid dimers. Dimers which have significantly asymmetric local intermolecular interactions are found to have a higher onset temperature for occupation of a second hydrogen atom site to be observed, indicating a greater energy asymmetry between the two configurations. Direct visualization of the electron density of hydrogen atoms within these dimers using high resolution X-ray diffraction data to characterize this disorder is shown to provide remarkably good agreement with that derived from neutron data

Tuning Proton Disorder in 3,5-Dinitrobenzoic Acid Dimers: the Effect of Local Environment

The carboxylic acid dimer is a frequently observed intermolecular association used in crystal engineering and design, which can show proton disorder across its hydrogen bonds. Proton disorder in benzoic acid dimers is a dynamic, temperature-dependent process whose reported occurrence is still relatively rare. A combination of variable temperature X-ray and neutron diffraction has been applied to demonstrate the effect of local crystalline environment on both the degree and onset of proton disorder in 3,5-dinitrobenzoic acid dimers. Dimers which have significantly asymmetric local intermolecular interactions are found to have a higher onset temperature for occupation of a second hydrogen atom site to be observed, indicating a greater energy asymmetry between the two configurations. Direct visualization of the electron density of hydrogen atoms within these dimers using high resolution X-ray diffraction data to characterize this disorder is shown to provide remarkably good agreement with that derived from neutron data

Total Syntheses of Multiple Cladiellin Natural Products by Use of a Completely General Strategy

The enantioselective total syntheses of 10 cladiellin natural products have been completed, starting from the known allylic alcohol <b>(+)-14</b>, which can be prepared in large quantities. The bridged tricyclic core of the cladiellins has been constructed via three ring-forming reactions: (i) an intramolecular reductive cyclization between an aldehyde and an unsaturated ester, mediated by samarium­(II) iodide, to form a tetrahydropyranol; (ii) reaction of a metal carbenoid, generated from a diazo ketone, with an ether to produce an ylide-like intermediate that rearranges to produce <i>E</i>- or <i>Z</i>-oxabicyclo­[6.2.1]-5-undecen-9-one; and (iii) a Diels–Alder cycloaddition reaction to construct the third ring found in the core structure of the cladiellins. The key ring-forming reaction, in which a diazo ketone is converted into a bridged bicyclic ether, can be tuned to give either of the isomeric oxabicyclo[6.2.1]-5-undecen-9-ones as the major product by switching from a copper to a rhodium catalyst and selecting the appropriate reaction conditions. The tricyclic products obtained from the three-step sequence involving the Diels–Alder cycloaddition reaction can be employed as advanced intermediates to prepare a wide range of cladiellin natural products

Total Syntheses of Multiple Cladiellin Natural Products by Use of a Completely General Strategy

The enantioselective total syntheses of 10 cladiellin natural products have been completed, starting from the known allylic alcohol <b>(+)-14</b>, which can be prepared in large quantities. The bridged tricyclic core of the cladiellins has been constructed via three ring-forming reactions: (i) an intramolecular reductive cyclization between an aldehyde and an unsaturated ester, mediated by samarium­(II) iodide, to form a tetrahydropyranol; (ii) reaction of a metal carbenoid, generated from a diazo ketone, with an ether to produce an ylide-like intermediate that rearranges to produce <i>E</i>- or <i>Z</i>-oxabicyclo­[6.2.1]-5-undecen-9-one; and (iii) a Diels–Alder cycloaddition reaction to construct the third ring found in the core structure of the cladiellins. The key ring-forming reaction, in which a diazo ketone is converted into a bridged bicyclic ether, can be tuned to give either of the isomeric oxabicyclo[6.2.1]-5-undecen-9-ones as the major product by switching from a copper to a rhodium catalyst and selecting the appropriate reaction conditions. The tricyclic products obtained from the three-step sequence involving the Diels–Alder cycloaddition reaction can be employed as advanced intermediates to prepare a wide range of cladiellin natural products

Synthesis, characterization and biological properties of novel ON donor bidentate Schiff bases and their copper(II) complexes

<p>Four novel ON donor Schiff bases (E)-3-((4-phenoxyphenylimino)methyl)benzene-1,2-diol (HL₁),(E)-3-((4-(4-biphenyloxy)phenyliminomethyl)benzene-1,2-diol (HL₂), (E)-3-((4-naphthoxyphenylimino)methyl)benzene-1,2-diol (HL₃), (E)-3-((4-(2-naphthoxy)phenylimino)methyl)benzene-1,2-diol (HL₄) and their copper(II) complexes bis((E)-3-((4-phenoxyphenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₁)₂) bis((E)-3-((4-(4-biphenyloxy)phenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₂)₂), bis((E)-3-((4-naphthoxyphenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₃)₂), bis((E)-3-((4-(2-naphthoxy)phenylimino)methyl)benzene-1,2-diol) copper(II) (Cu(L₄)₂) have been synthesized and characterized by spectroscopic (FTIR, NMR, UV–visible) and elemental analysis. The crystal structures of HL₁, HL₂, HL₃_, and HL₄ have been determined, which reveal intramolecular N-H⋯O (HL₁, HL₂, HL₃_, and HL₄) hydrogen bonds in the solid state. Keto-amine and enol-imine tautomerism is exhibited by the Schiff bases in solid and solution states. The Schiff bases and their copper(II) complexes have been screened for their biological activities. In antimicrobial assays (antibacterial and antifungal), HL₄ showed promising results against all strains through dual inhibition property while the rest of the compounds showed activity against selective strains. On the other hand, in cytotoxic, DPPH, and inhibition of hydroxyl (OH) free radical-induced DNA damage assays, the results were found significantly correlated with each other, <i>i.e.</i> the ligands HL₁ and HL₂ showed moderate activity while their complexes Cu(L₁)₂ and Cu(L₂)₂ exhibited prominent increase in activity. As the results of these assays are supporting each other, it represents the strong positive correlation and antioxidant nature of investigated compounds.</p