76 research outputs found
Photoredox approach to N-Acyl-N'-aryl-N,N'-aminals using enamides and their conversion to γ-lactams
A photoredox catalytic approach to synthetically valuable N-acyl-N'-aryl-N,N'-aminals is described. This method uses the addition of a radical precursor to enamides, with subsequent interception of the cationic iminium intermediate with an arylamine. The reaction has been shown to be compatible with electron-rich and electron-deficient arylamines, and moderate to good levels of diastereoselectivity can be attained using a chiral enamide. Furthermore, the N-acyl-N'-aryl-N,N'-aminal reaction products can be readily cyclized, providing a novel synthetic route to valuable γ-lactams
Isolation and structure determination of the first example of the azeto[2,3-c]quinolizinedione ring system
An unexpected azeto[2,3-c]quinolizinedione has been isolated during synthetic studies on the base catalyzed condensation of ethyl 6-methylpyridin-2(1H)-on-1-ylacetate with benzil. Closure of a fused four-membered azetidinone ring occurred when potassium hexamethyldisilazide was employed as the base. The structure of the product was confirmed by synchrotron X-ray crystallography. A possible mechanism for the formation of the product is considered
The selective mono and difunctionalization of carbocyclic cleft molecules with pyridyl groups and X-ray crystallographic analysis
The diesterification and selective mono and dialkylation of carbocyclic analogues of Tröger’s base with pyridyl groups has been achieved in high yield and good selectivity giving access to a novel range of cleft molecules capable of binding events. Reaction conditions for the selective functionalization of this carbocyclic cleft molecule are discussed as well as the solid state structures of these newly synthesized ligands
Novel fluorinated benzimidazole-based scaffolds and their anticancer activity in vitro
A small library of twelve, structurally diverse, fluoroaryl benzimidazoles was prepared using a simple synthetic strategy employing SNAr reactions. This allowed rapid assembly of heterocyclic structures containing linked and tethered fluoroaryl benzimidazoles. X-ray crystal structures of seven compounds were obtained including those of two macrocyclic compounds containing 21- and 24-membered rings. Three tethered fluoroaryl benzimidazole derivatives demonstrated micromolar inhibition against K-562 and MCF-7 cell lines. These compounds, in addition to 1-tetrafluoropyrid-4-yl-2-tetrafluoropyrid-4-ylsulfanyl-1H-benzimidazole, also demonstrated micromolar inhibition against G361 and HOS cell lines. Two of the compounds were found to activate caspases leading to apoptosis
Multiple photoluminescence from pyrene-fused hexaarylbenzenes with aggregation enhanced emission features
Multiple photoluminescence, involved in monomer emission, excimer emission and charge transfer emission origin from new pyrene-fused hexaarylbenzenes (HAB) compounds were observed, which were designed and synthesized (in high yield) via the Diels-Alder reaction of bis(2-tert-butylpyren-6-yl)acetylene and tetraphenylcyclopentadienone. Although the distinction of between two molecules arises only from the geometrical position of one of the pyrenes, the NMR spectra, the crystal packing and the physicochemical properties of these pyrene-based HAB hybrids are distinctly different both in their solution state and in aggregation-state. The X-ray diffraction analysis clearly indicated that the pyrene moieties in this system would form different crystal packing in crystal state that can induce a fantastic multiple photoluminescence phenomenon
Structural and Thermodynamic Study of the Complexes of Nd(III) with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetramethyl-3-oxa-glutaramide and the Acid Analogues
The thermodynamics of NdÂ(III) complexes
with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-3-oxa-glutaramide (TMOGA, L<sup>I</sup>), <i>N</i>,<i>N</i>-dimethyl-3-oxa-glutaramic
acid (DMOGA,
HL<sup>II</sup>), and oxydiacetic acid (ODA, H<sub>2</sub>L<sup>III</sup>) in aqueous solutions was studied. Stability constants, enthalpies,
and entropies of complexation were determined by spectrophotometry,
potentiometry, and calorimetry. The stability constants of corresponding
NdÂ(III) complexes decrease in the following order: NdÂ(III)/L<sup>III</sup> > NdÂ(III)/L<sup>II</sup> > NdÂ(III)/L<sup>I</sup>. For all
complexes,
the enthalpies of complexation are negative and the entropies of complexation
are positive, indicating that the complexation is driven by both enthalpy
and entropy. Furthermore, from L<sup>III</sup> to L<sup>II</sup>,
and to L<sup>I</sup>, the enthalpy of complexation becomes more exothermic
and the entropy of complexation less positive, suggesting that the
substitution of a carboxylate group with an amide group on the ligands
enhances the enthalpy-driven force but weakens the entropy-driven
force of the complexation with NdÂ(III). Crystal structures of three
1:3 NdÂ(III) complexes, NdÂ(L<sup>I</sup>)<sub>3</sub>(ClO<sub>4</sub>)<sub>3</sub> (<b>I</b>), NdÂ(L<sup>I</sup>)<sub>3</sub>(NO<sub>3</sub>)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub> (<b>II</b>), and NdÂ(L<sup>II</sup>)<sub>3</sub>(H<sub>2</sub>O)<sub>7.5</sub> (<b>III</b>), were determined by single-crystal X-ray diffraction
and compared with the structure of a 1:3 NdÂ(III)/L<sup>III</sup> complex
in the literature, Na<sub>3</sub>NdL<sup>III</sup><sub>3</sub>(NaClO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub> (<b>I</b><b>V</b>). In all four structures, the ligands are tridentate and
NdÂ(III) is nine-coordinated with similar distorted tricapped trigonal
prism geometry by three ether oxygen atoms capped on the three faces
of the prism, and six oxygen atoms from the ketone group or carboxyl
group at the corners. The absorption spectra of NdÂ(III) in solutions
showed very similar patterns as NdÂ(III) formed successive 1:1, 1:2,
and 1:3 complexes with L<sup>I</sup>, L<sup>II</sup>, and L<sup>III</sup>, respectively, implying that the NdÂ(III) complexes with the three
ligands have similar coordination geometries in aqueous solutions,
as observed in the solids
Structural and Thermodynamic Study of the Complexes of Nd(III) with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetramethyl-3-oxa-glutaramide and the Acid Analogues
The thermodynamics of NdÂ(III) complexes
with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-3-oxa-glutaramide (TMOGA, L<sup>I</sup>), <i>N</i>,<i>N</i>-dimethyl-3-oxa-glutaramic
acid (DMOGA,
HL<sup>II</sup>), and oxydiacetic acid (ODA, H<sub>2</sub>L<sup>III</sup>) in aqueous solutions was studied. Stability constants, enthalpies,
and entropies of complexation were determined by spectrophotometry,
potentiometry, and calorimetry. The stability constants of corresponding
NdÂ(III) complexes decrease in the following order: NdÂ(III)/L<sup>III</sup> > NdÂ(III)/L<sup>II</sup> > NdÂ(III)/L<sup>I</sup>. For all
complexes,
the enthalpies of complexation are negative and the entropies of complexation
are positive, indicating that the complexation is driven by both enthalpy
and entropy. Furthermore, from L<sup>III</sup> to L<sup>II</sup>,
and to L<sup>I</sup>, the enthalpy of complexation becomes more exothermic
and the entropy of complexation less positive, suggesting that the
substitution of a carboxylate group with an amide group on the ligands
enhances the enthalpy-driven force but weakens the entropy-driven
force of the complexation with NdÂ(III). Crystal structures of three
1:3 NdÂ(III) complexes, NdÂ(L<sup>I</sup>)<sub>3</sub>(ClO<sub>4</sub>)<sub>3</sub> (<b>I</b>), NdÂ(L<sup>I</sup>)<sub>3</sub>(NO<sub>3</sub>)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub> (<b>II</b>), and NdÂ(L<sup>II</sup>)<sub>3</sub>(H<sub>2</sub>O)<sub>7.5</sub> (<b>III</b>), were determined by single-crystal X-ray diffraction
and compared with the structure of a 1:3 NdÂ(III)/L<sup>III</sup> complex
in the literature, Na<sub>3</sub>NdL<sup>III</sup><sub>3</sub>(NaClO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub> (<b>I</b><b>V</b>). In all four structures, the ligands are tridentate and
NdÂ(III) is nine-coordinated with similar distorted tricapped trigonal
prism geometry by three ether oxygen atoms capped on the three faces
of the prism, and six oxygen atoms from the ketone group or carboxyl
group at the corners. The absorption spectra of NdÂ(III) in solutions
showed very similar patterns as NdÂ(III) formed successive 1:1, 1:2,
and 1:3 complexes with L<sup>I</sup>, L<sup>II</sup>, and L<sup>III</sup>, respectively, implying that the NdÂ(III) complexes with the three
ligands have similar coordination geometries in aqueous solutions,
as observed in the solids
Structural and Thermodynamic Study of the Complexes of Nd(III) with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetramethyl-3-oxa-glutaramide and the Acid Analogues
The thermodynamics of NdÂ(III) complexes
with <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-3-oxa-glutaramide (TMOGA, L<sup>I</sup>), <i>N</i>,<i>N</i>-dimethyl-3-oxa-glutaramic
acid (DMOGA,
HL<sup>II</sup>), and oxydiacetic acid (ODA, H<sub>2</sub>L<sup>III</sup>) in aqueous solutions was studied. Stability constants, enthalpies,
and entropies of complexation were determined by spectrophotometry,
potentiometry, and calorimetry. The stability constants of corresponding
NdÂ(III) complexes decrease in the following order: NdÂ(III)/L<sup>III</sup> > NdÂ(III)/L<sup>II</sup> > NdÂ(III)/L<sup>I</sup>. For all
complexes,
the enthalpies of complexation are negative and the entropies of complexation
are positive, indicating that the complexation is driven by both enthalpy
and entropy. Furthermore, from L<sup>III</sup> to L<sup>II</sup>,
and to L<sup>I</sup>, the enthalpy of complexation becomes more exothermic
and the entropy of complexation less positive, suggesting that the
substitution of a carboxylate group with an amide group on the ligands
enhances the enthalpy-driven force but weakens the entropy-driven
force of the complexation with NdÂ(III). Crystal structures of three
1:3 NdÂ(III) complexes, NdÂ(L<sup>I</sup>)<sub>3</sub>(ClO<sub>4</sub>)<sub>3</sub> (<b>I</b>), NdÂ(L<sup>I</sup>)<sub>3</sub>(NO<sub>3</sub>)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub> (<b>II</b>), and NdÂ(L<sup>II</sup>)<sub>3</sub>(H<sub>2</sub>O)<sub>7.5</sub> (<b>III</b>), were determined by single-crystal X-ray diffraction
and compared with the structure of a 1:3 NdÂ(III)/L<sup>III</sup> complex
in the literature, Na<sub>3</sub>NdL<sup>III</sup><sub>3</sub>(NaClO<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub> (<b>I</b><b>V</b>). In all four structures, the ligands are tridentate and
NdÂ(III) is nine-coordinated with similar distorted tricapped trigonal
prism geometry by three ether oxygen atoms capped on the three faces
of the prism, and six oxygen atoms from the ketone group or carboxyl
group at the corners. The absorption spectra of NdÂ(III) in solutions
showed very similar patterns as NdÂ(III) formed successive 1:1, 1:2,
and 1:3 complexes with L<sup>I</sup>, L<sup>II</sup>, and L<sup>III</sup>, respectively, implying that the NdÂ(III) complexes with the three
ligands have similar coordination geometries in aqueous solutions,
as observed in the solids
Models for Copper Dynamic Behavior in Doped Cadmium dl-Histidine Crystals: Electron Paramagnetic Resonance and Crystallographic Analysis
Electron
paramagnetic resonance and crystallographic studies of copper-doped cadmium dl-histidine, abbreviated as CdDLHis, were undertaken to gain further
understanding on the relationship between site structure and dynamic
behavior in biological model complexes. X-ray diffraction measurements
determined the crystal structure of CdDLHis at 100 and 298 K. CdDLHis
crystallizes in the monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i> with two cadmium complexes per asymmetric
unit. In each complex, the Cd is hexacoordinated to two histidine
molecules. Both histidines are l in one complex and d in the other. Additionally, each complex contains multiple waters
of varying disorder. Single crystal EPR spectroscopic splitting (<b>g</b>) and copper hyperfine (<b>A</b><sup><b>Cu</b></sup>) tensors at room temperature (principal values: <b>g</b> = 2.249, 2.089, 2.050; <b>A</b><sup><b>Cu</b></sup> =
−453, −30.5, −0.08 MHz) were determined from
rotational experiments. Alignments of the tensor directions with the
host structure were used to position the copper unpaired d<sub><i>x</i><sup>2</sup>‑<i>y</i><sup>2</sup></sub> orbital in an approximate plane made by four proposed ligand atoms:
the <i>N</i>-imidazole and <i>N</i>-amino of one
histidine, and the <i>N</i>-amino and <i>O</i>-carboxyl of the other. Each complex has two such planes related
by noncrystallographic symmetry, which make an angle of 65° and
have a 1.56 Ă… distance between their midpoints. These findings
are consistent with three interpretations that can adequately explain
previous temperature-dependent EPR powder spectra of this system:
(1) a local structural distortion (static strain) at the copper site
has a temperature dependence significant enough to affect the EPR
pattern, (2) the copper can hop between the two sites in each complex
at high temperature, and (3) there exists a dynamic Jahn–Teller
effect involving the copper ligands
- …