Synthesis of (4Z)‐4‐(Arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones by the Reaction of Ethyl (2Z)‐3‐Aryl‐2‐isothiocyanatoprop‐2‐enoates with Organolithium Compounds

A convenient one‐pot method for the preparation of (4Z)‐4‐(arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones 2 and 3 from ethyl (2Z)‐3‐aryl‐2‐isothiocyanatoprop‐2‐enoates 1 , which can be easily prepared from ethyl 2‐azidoacetate and aromatic aldehydes, has been developed. Thus, these α‐isothiocyanato α,β‐unsaturated esters were treated with organolithium compounds, including lithium enolates of acetates, to provide 5‐substituted (4Z)‐4‐(arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones, 2 , and 2‐[(4Z)‐(4‐arylmethylidene)‐5‐ethoxy‐2‐thioxo‐1,3‐oxazolidin‐5‐yl]acetates, 3 .     

Multi‐Fluorinated Azido Coumarins for Rapid and Selective Detection of Biological H2S in Living Cells

Hydrogen sulfide (H₂S) is an endogenously produced gaseous signaling molecule with multiple biological functions. In order to visualize the endogenous in situ production of H₂S in living cells in real time, here we developed multi‐fluorinated azido coumarins as fluorescent probes for the rapid and selective detection of biological H₂S. Kinetic studies indicated that an increase in fluorine substitution leads to an increased rate of H₂S‐mediated reduction reaction, which is also supported by our theoretical calculations. To our delight, tetra‐fluorinated coumarin 1 could react with H₂S fast (t_1/2≈1 min) and selectively, which could be further used for continuous enzymatic assays and for visualization of intracellular H₂S. Bioimaging results obtained with 1 revealed that d ‐Cys could induce a higher level of endogenous H₂S production than l ‐Cys in a time‐dependent manner in living cell.     

A rare ferromagnetically coupled asymmetric doubly azido bridged copper(II) dimer with an N,N, O donor Schiff base

A new end-to-end (EE) doubly azido bridged dinuclear complex [Cu₂L₂(μ_1,3-N₃)₂] (1) [where L = (E)-4-(2-(dimethylamino)ethylimino)-1,1,1-trifluoropentan-2-one)] has been synthesized and characterized by elemental and spectroscopic techniques. Single crystal X-ray diffraction analysis reveals that the dimeric complex possesses a center of inversion. Each copper atom in 1 is in a distorted square pyramidal geometry with a CuN₄O chromophore as revealed from the τ value, 0.19. The four basal positions are occupied by two imine N and one keto O atom of the Schiff base and one N atom from the azide anion. Another N atom from a coordinated azide occupies the apical position. Temperature dependent magnetic susceptibility of 1 was fitted using the Bleaney–Bowers expression which led to the parameters J = 13.6 cm⁻¹ and R = 3.4 × 10⁻⁵. It indicates a ferromagnetic interaction through the double azido bridges connecting the individual copper Schiff base units.     

(HMgN3)n(n=1–5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论在B3LYP/6-311G^*水平上对叠氮化合物(HMgN₃)_n(n=1–5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构. 并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究. 结果表明:HMgN₃团簇最稳定结构为直线型;(HMgN₃)_n(n=2,5)团簇最稳定结构为叠氮基中N原子和金属原子相连构成Mg–N–Mg结构;(HMgN₃)_n(n=3,4)团簇最稳定结构为叠氮基与Mg原子相互链接形成的环状结构. 团簇最稳定结构中金属Mg原子均显示正电性,H原子均显示负电性,叠氮基中间的N原子显示正电性、两端的N原子显示负电性,且与Mg原子直接作用的N原子负电性更强. Mg–N键和Mg–H键为典型的离子键,叠氮基内N原子之间是共价键. 团簇最稳定结构的红外光谱分为三部分,其最强振动峰均位于2258–2347 cm^-1,振动模式为叠氮基中N–N键的反对称伸缩振动. 叠氮基在团簇和晶体中结构不变,始终以直线型存在. 稳定性分析显示,(HMgN₃)₃团簇相对于其他团簇更为稳定. 关键词： 3)_n(n=1–5)团簇')" href="#">(HMgN₃)_n(n=1–5)团簇 叠氮基 密度泛函理论 结构与性质     

Selectively Dendronized Cellulose: Synthesis and Characterization

Selectively dendronized cellulose at C‐6 was synthesized homogeneously (in DMSO) and heterogeneously (in methanol) by the conversion of 6‐azido‐6‐deoxy cellulose (degree of substitution, DS 0.75) with polyamidoamine (PAMAM) dendrons possessing an ethynyl focal moiety via the copper‐catalyzed Huisgen reaction (click reaction) under mild conditions. First to third generation of PAMAM‐triazolo cellulose derivatives with DS values of up to 0.69 could be prepared, which are soluble in organic solvents (DMSO, DMF) and in water. The novel biopolymer derivatives were characterized by elemental analysis, FTIR, and NMR spectroscopic methods, showing no impurities and no conversion at the secondary positions.

     

New Azido Coumarins as Potential Agents for Fluorescent Labeling and Their “Click” Chemistry Reactions for the Conjugation with closo-Dodecaborate Anion

Novel fluorescent 7-methoxy- and 7-(diethylamino)-coumarins modified with azido-group on the side chain have been synthesized. Their photophysical properties and single crystals structure characteristics have been studied. In order to demonstrate the possibilities of fluorescent labeling, obtained coumarins have been tested with closo-dodecaborate derivative bearing terminal alkynyl group. Cu^I catalyzed Huisgen 1,3-dipolar cycloaddition reaction has led to fluorescent conjugates formation. The absorption–emission spectra of the formed conjugates have been presented. The antiproliferative activity and uptake of compounds against several human cell lines were evaluated.     

Generation of Pseudocontact Shifts in Proteins with Lanthanides Using Small “Clickable” Nitrilotriacetic Acid and Iminodiacetic Acid Tags

Pseudocontact shifts (PCS) induced by paramagnetic lanthanide ions provide unique long‐range structural information in nuclear magnetic resonance (NMR) spectra, but the site‐specific attachment of lanthanide tags to proteins remains a challenge. Here we incorporated p‐azido‐phenylalanine (AzF) site‐specifically into the proteins ubiquitin and GB1, and ligated the AzF residue with alkyne derivatives of small nitrilotriacetic acid and iminodiacetic acid tags using the Cu^I‐catalysed “click” reaction. These tags form lanthanide complexes with no or only a small net charge and produced sizeable PCSs with paramagnetic lanthanide ions in all mutants tested. The PCSs were readily fitted by single magnetic susceptibility anisotropy tensors. Protein precipitation during the click reaction was greatly alleviated by the presence of 150 mM NaCl.     

α-Azidopolynitroalkanes. Synthesis and vibrational spectra

Methods for the preparation of α-azidopolynitroalkanes by reactions of polynitroalkanes or α-(difluoroamino)polynitroalkanes with NaN₃ were developed. In the case of tetranitromethane, one or two nitro groups can be substituted, depending on the reaction conditions. The reaction of 1,1,1-trinitroethane with NaN₃ affords nitro-1,2,3-triazole, together with 1-azido-1,1-dinitroethane. The IR spectra of α-azidopolynitroalkanes were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 338–341, February, 1997.     

Clusteraufbau durch Photolyse von Azidokomplexen des Platins und Golds. Synthesen und Kristallstrukturen von [(Ph3PAu)6(AuCl)3Pt(CO)], [(dppe)PtCo2(CO)7] und [(Ph3PAu)4Pt(dppe)](PF6)2

Cluster Synthesis by Photolysis of Azido Complexes of Platinum and Gold. Syntheses and Crystal Structures of [(Ph₃PAu)₆(AuCl)₃Pt(CO)], [(dppe)PtCo₂(CO)₇] and [(Ph₃PAu)₄Pt(dppe)](PF₆)₂ Photolysis of a mixture of Ph₃PAuN₃, Ph₃PAuCl and (Ph₃P)₂Pt(N₃)₂ in THF yields after chromatographic separation with CH₂Cl₂/EtOH as eluens the cluster [(Ph₃PAu)₆(AuCl)₃Pt(CO)] ( 1 ). It crystallizes in the triclinic space group P1 with the lattice parameters a = 2 139.3(4), b = 2 457.1(4), c = 2 561.9(1) pm, α = 79.74(9)°, β = 80.06(6)°, γ = 66.05(5)°, Z = 4. The nine gold atoms form a fragment of an icosahedron with the platinum atom in its center. Upon photolysis of (dppe)Pt(N₃)₂ with Co₂(CO)₈ in THF one m?₂-CO ligand of the cobalt carbonyl is substituted by a (dppe)Pt group. The resulting cluster [(dppe)PtCo₂(CO)₇] ( 2 ) crystallizes monoclinically in the space group P2₁/n with a = 1 303.9(3), b = 1 768.1(8), c = 1 461.4(4) pm, β = 102.81(1)°, Z = 4. Photolysis of 2 with excess Ph₃PAuN₃ affords the clusters [(Ph₃PAu)₄Pt(dppe)]²⁺ ( 3 ), and [(Ph₃PAu)₆AuCo₂(CO)₆]⁺. 3 crystallizes with PF as counterions in the triclinic space group P1 with a = 1 369.1(4), b = 1 505.0(4), c = 2 773.0(8) pm, α = 84.74(1)°, β = 87.37(2)°, γ = 65.94(2)°, Z = 2. The Au₄Pt skeleton of 3 forms a trigonal bipyramid with the platinum atom in equatorial position.     

Synthesis of dimethylphosphorylamino diazo esters by a selective tandem Staudinger/Arbuzov rearrangement sequence of azido diazo esters with trimethylphosphite

γ-Azido-α-diazo-β-keto esters react selectively with trimethylphosphite by a tandem Staudinger/Arbuzov rearrangement sequence, furnishing γ-(dimethylphosphorylamino)-α-diazo-β-keto esters in good yield under mild conditions. Collected X-ray data for the novel diazo phosphoramides confirm the proposed chemoselectivity.