Synthesis of 6, 9, 11-Trihydroxy-6a, 12a-dehydrorotenoid

6, 9, 11-Trihydroxy-6a, 12a-dehydrorotenoid 1 (coccineone B) was synthesized from 2-hydroxybenzaldehyde 2 and phloroglucinol.     

Molecular quadrangle formation from a diuranium μ-η6,η6-toluene complex

A new inverted sandwich of a μ-η(6),η(6)-toluene diuranium complex reacted with quinoxaline to form a tetranuclear macrocycle with ferrocene diamide uranium(IV) vertices and reduced quinoxaline edges.     

Deprotonation of a Seemingly Hydridic Diborane(6) To Build a B−B Bond

Deprotonation of the doubly arylene-bridged diborane(6) derivative 1 H₂ with (Me₃Si)₃CLi or (Me₃Si)₂NK gives the B−B σ-bonded species M[ 1 H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4′-di-tert-butyl-2,2′-biphenylylene). With nBuLi as the base, the yield of Li[ 1 H] drops to 20 % and the 1,1-bis(9-borafluorenyl)butane Li[ 2 H] is formed as a side product (30 %). In addition to the 1,1-butanediyl fragment, the two boron atoms of Li[ 2 H] are linked by a μ-H bridge. In the closely related molecule Li[ 3 H], the corresponding μ-H atom can be abstracted with (Me₃Si)₃CLi to afford the B−B-bonded conjugated base Li₂[ 3 ] (THF, 150 °C; 15 %). Li[ 1 H] and Li[ 2 H] were characterized by NMR spectroscopy and X-ray crystallography.     

Zn7Cu6: a magic cluster of brass?

Density functional theory was applied to a series of 13-atom Zn–Cu alloy clusters. We did a thorough search for the low-energy isomers by global optimization, plus explicit optimization of all homotops of the icosahedron. Structures of copper rich clusters tend to be compact, often icosahedra, whereas zinc rich clusters ( ${{\rm Zn}_8{\rm Cu}_{5}^{+}}$ , Zn₉Cu₄, Zn₁₁Cu₂) have compact copper cores surrounded by an incomplete shell of solvating Zn atoms. The icosahedral structure, low total energy, and large hardness of Zn₇Cu₆ indicate that it has special stability among Zn _x Cu _y clusters. However, Zn₇Cu₆ has many low lying isomers and a small cohesive energy compared to brass, which suggest that it is not stable in a broader sense.     

Crystal Structure of a Hexanuclear Silver(Ⅰ) Compound [Ag_6L_6~6]·4DMF and Luminescence Discussion of a Series of Silver(Ⅰ) Clusters

A new silver(Ⅰ) compound 6 ([Ag6L66]·4DMF) containing thiosemicarbazone with the group of 2-chloro-1-benzene was synthesized and structurally characterized by single-crystal X-ray diffraction, elemental analysis and fluorescence spectrum. The title compound 6 crystallizes in monoclinic, space group C2/c with a = 26.9236(18), b = 15.2553(8), c = 24.6237(13) , β = 103.0680(10)°, V = 9851.7(10)3, C58H66Ag6Cl6N20O3S6, Mr = 2143.59, Dc = 1.445 g/cm3, μ(MoKα) = 1.503 mm-1, F(000) = 4232, Z = 4, the final R = 0.0565 and wR = 0.1654 for 5831 observed reflections (Ⅰ > 2σ(Ⅰ)). Similar to the structure of the compounds we have reported, compound 6 also exhibits a hexanuclear silver(Ⅰ) cluster. In the cluster, the S atom of ligand L6 (L6 = 2-chloro-1-benzaldehyde thiosemicarbazone) served as a triply bridged chelator to connect the six silver atoms into a Ag6L66 cluster. The luminescence property of compound 6 was investigated at room temperature and compared with other similar compounds in order to find the factors influencing their luminescent property.     

6-Hydroxymethyltriazolyl-6-deoxy-β-cyclodextrin: a highly water soluble and structurally well-defined β-cyclodextrin click cluster

The structural, physical, and biological properties of heptakis{6-(4-hydroxymethyl-1H-[1,2,3]triazol-1-yl)-6-deoxy}-β-cyclodextrin (HTβCD) were investigated by a variety of methods, including NMR, UV/vis, circular dichroism spectroscopy, computer modeling, turbidity testing, K_a measurements, and the MTT assay. The experimental results suggest that HTβCD is structurally well-defined, highly water-soluble, and has low cytotoxicity. These advantages of HTβCD versus β-CD indicate that β-cyclodextrin click clusters may function both as host molecules and as potential, alternative excipients to β-CD.     

A potassium–18-crown-6 salt of a cyclic myo-inositol phosphate

The six-membered phosphorinane ring in (1,4,7,10,13,16-hexaoxa­cyclo­octa­decane)­potassium 2-O-benzoyl-1,3,5-O-methyl­idyne-myo-in­osi­tol 4,6-cyclo­phosphate trihydrate, [K(C₁₂H₂₄O₆)](C₁₄H₁₂O₉P)·3H₂O, has a boat rather than a chair conformation. The K⁺ ion is eight-coordinate and is connected to one of the phosphate O atoms, one of the O atoms of the myo-inositol residue and the six O atoms of the crown ether.     

Crystal structure of a hydroxo-bridged dimeric uranyl complex with a 2,2′:6′,2″-terpyridine ligand

A new dimeric compound [{UO₂(μ-OH)(terpy)}₂](ClO₄)₂·0.67CH₃CN, containing an uranyl cation and a tridentate 2,2′:6′,2″-terpyridine (terpy) ligand, is synthesized from an acetonitrile solution of uranyl perchlorate and terpy. The crystal structure of the compound is determined by single crystal X-ray diffraction. The crystal structure shows the formation of symmetric and asymmetric cationic hydroxo-bridged uranyl dimers. The uranium atoms adopt a distorted pentagonal bipyramidal configuration with a UO₄N₃ coordination environment formed by two uranyl O atoms, three N atoms from the terpy ligand, and two O atoms from the hydroxide anions.     

Sugar chemistry without protecting groups: a novel regioselective synthesis of 6-O-acyl-D-glucopyranoses and methyl-6-O-acyl-α-D-glucopyranosides

The primary hydroxyl groups of α-$\text{D}$-glucose and methyl-α-$\text{D}$-glucoside were selectively esterified by treating the free sugars with $\text{N}$-acylthiazolidine-2-thiones, thus affording respectively 6-$\text{O}$-acyl-$\text{D}$-glucopyranoses and methyl-6-$\text{O}$-acyl-α-$\text{D}$-glucopyranosides in high yields. This new reaction is compared with our previous synthesis of 1-$\text{O}$-acyl-β-$\text{D}$-glucopyranoses from β-$\text{D}$-glucose and interpreted in terms of anomeric effect.     

Synthesis and X‐Ray Analysis of a New [6]Helicene

A new disubstituted hexahelicene derivative 3 bearing methoxy functions at positions 3 and 14 has been prepared in racemic form through a Heck reaction followed by photocyclodehydrogenation. Suitable crystals of rac‐3 were analyzed by X‐ray crystallography and showed similar geometry to the structure of hexahelicene itself. Deprotection of 3 using boron tribromide led to 3,14‐dihydroxyhexahelicene 4 in quantitative yield. The complexation of transition metal atoms seemed to be quite possible by these two bidentate hexahelicene derivatives.     

Triple C-H Bond Activation of a Nickel-Bound Methyl Group: Synthesis and X-Ray Structure of a Carbide Cluster (NiCp)(6)(μ(6)-C)

A new hexanuclear cyclopentadienylnickel carbide cluster (NiCp)(6)(μ(6)-C) (1) was obtained through the thermolysis of the alkene complex [NiCp(CH(3))(η(2)-CH(2)═CHC(4)H(9))] (4). The X-ray molecular structure of 1 (monoclinic; P2(1)/c; Ni-C(carbide) = 1.767(4)-2.109(4) ?) reveals a highly deformed octahedral arrangement of nickel atoms with two octahedron edges opened (Ni-Ni bonding distances = 2.410(1)-2.623(1) ?, Ni···Ni nonbonding distances = 3.107(2) and 3.108(2) ?). Cluster 1 is the first example of a homoleptic, cyclopentadienylnickel carbide cluster. Moreover, (13)C-labeling studies proved that the carbido ligand in cluster 1 originated from the Ni-bound methyl group. This transformation requires a triple C-H bond activation in the methyl group, which has not been observed so far for late transition metal compounds.     

Structural characterization of a sodium perchlorate−acridino-18-crown-6 ether complex

This paper describes the X-ray crystal structure of a complex of acridino-18-crown-6 ether (S,S)-2 and sodium perchlorate. The structure shows a homodimer in the crystal and suggests the potential for π–π bonded interactions between the monomers. The average distance of the two tricyclic units (3.49 ± 0.1 Å) may indicate a considerably strong π–π interaction. Fluorescence titration was performed in order to determine the stoichiometry and stability constant (K _s) of the sodium ion-(S,S)-2 complex. Based on the global fitting of the fluorescence spectra, we suggest the formation of a complex with 1:1 ligand to metal ion ratio, and the logK value determined by nonlinear regression analysis was 5.23.     

SAMPL6 host–guest blind predictions using a non equilibrium alchemical approach

In this paper, we compute, by means of a non equilibrium alchemical technique, called fast switching double annihilation methods (FSDAM), the absolute standard dissociation free energies of the the octa acids host–guest systems in the SAMPL6 challenge initiative. FSDAM is based on the production of canonical configurations of the bound and unbound states via enhanced sampling and on the subsequent generation of hundreds of fast non-equilibrium ligand annihilation trajectories. The annihilation free energies of the ligand when bound to the receptor and in bulk solvent are obtained from the collection of work values using an estimate based on the Crooks theorem for driven non equilibrium processes. The FSDAM blind prediction, relying on the normality assumption for the annihilation work distributions, ranked fairly well among the submitted blind predictions that were not adjusted with a linear corrections obtained from retrospective data on similar host guest systems. Improved results for FSDAM can be obtained by post-processing the work data assuming mixtures of normal components.     

6-O-methylkrigeine, a new amaryllidaceae alkaloid from Nerine huttoniae Schönland

A novel Amaryllidaceae alkaloid, 6-O-methylkrigeine, has been isolated from Nerine huttoniae and the configuration was elucidated by 1-D and 2-D (1)H-NMR, (13)C-NMR, HRMS and optical rotation.     

Stereoselective synthesis of C-6 hydroxy tricyclic sulfone as a γ-secretase inhibitor

The synthesis of a C-6 hydroxy tricyclic sulfone was described with two key reactions: the Suzuki coupling and the regioselective and stereoselective cis ring opening of the epoxide. Overall, the 14-step synthesis was achieved in 2.1% yield.     

Synthesis,structural characterization and magnetic properties of a novel metallacrown [Fe6(amshz)6(C3H7NO)6]·6CH3OH

The novel 18-metallacrown-6 metallamacrocycle, with the formula of [Fe₆(amshz)₆(C₃H₇NO)₆]·6CH₃OH (1), has been synthesized by the self-assembly reaction of iron ions with N-substituted salicylhydrazide ligands. Six Fe(III) ions and six deprotonated N-acetyl-3-methylsalicylhydrazide (amshz^3?) ligands construct a planar 18-membered ring based on Fe–N–N–Fe linkage. Due to the coordination, the ligand enforces the stereochemistry of the Fe³⁺ ions as a propeller shape with alternating …ΔΛΔΛ… configurations. There exists a strong antiferromagnetic exchange interaction with μ_eff = 12.54 μ_B at 300 K between the Fe(III) spin 5/2 centers.     

Synthesis and application of a novel single-isomer mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-cyclodextrin chloride as a chiral selector in capillary electrophoresis

A novel positively charged single-isomer of β-cyclodextrin, mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-CD chloride (dhypy-CDCl), was synthesized and employed as a chiral selector for the first time in capillary electrophoresis (CE) for the enantioseparation of anionic and ampholytic acids. The effects of the running buffer pH, chiral selector concentration, analyte structure and organic modifier on the enantioseparation were studied in detail. The chiral selectivity and resolution for most of the studied analytes decreased as the buffer pH increased in the range of 6.0–9.0. Increasing selector concentration led to decreased effective mobility, increased chiral selectivity and resolution for most of the studied analytes. Moreover, the hydroxyl groups located on the dihydroxypyrrolidine substituent of the dhypy-CDCl could have influence on the chiral separation.     

First-transition-metal complexes containing the ligands 6-amino-6-methylperhydro-1,4-diazepine (AAZ) and a new functionalized derivative: can AAZ act as a mimetic ligand for 1,4,7-triazacyclononane?

The structure and physicochemistry of the [Ni(II)(AAZ)(2)](ClO(4))(2) (1) complex (AAZ = 6-amino-6-methylperhydro-1,4-diazepine), as a system that is able to mimic some important chelate properties of 1,4,7-triazacyclononane, are reported. The syntheses of a new unsymmetric AAZ-functionalized ligand and the structure of its first heterodinuclear Fe(III)Zn(II) complex are also presented.