Nickel-catalyzed CH trifluoromethylation of pyridine N-oxides with Togni’s reagent

The first nickel-catalyzed CH trifluoromethylation of pyridine N-oxides with Togni’s reagent has been achieved. Trifluoromethylation proceeds smoothly under mild conditions with moderate functional group compatibility. Notable advantages of this method include the using of low cost of nickel catalyst, and its simple convenient operation.     

Efficient synthesis of α-substituted-α-arylmethyl phosphonates using trichloroacetimidate CC coupling method

A simple convenient protocol for the synthesis of diethyl α,α-diaryl methylphosphonate derivatives 5a-f, 6b-f, 7a-f and 8a-f, diethyl α-alkenyl α-aryl methylphosphonates 9a-d and 10a-d and α-(oxoalkyl) α-aryl methylphosphonate 11a-d and 12a-d is described. Trichloroacetimidates 3a-d were treated with activated arenes, styrene, allyltrimethylsilane or silylenol ethers C-nucleophiles in the presence TMSOTf to afford the desired products in good yields and short reaction time.     

A New Iridoid Glycoside and a New Iridoid from Pedicularis kansuensis f. albiflora

A new iridoid glycoside 1 and a new iridoid 2 were isolated from the whole plant of Pedicularis kansuensis f. albiflora. Their structures were elucidated by spectroscopie methods.     

A New lridoid Glycoside and a New lridoid from Pedicularis kansuensis f. albiflora

A new iridoid glycoside 1 and a new iridoid 2 were isolated from the whole plant of Pedicularis kansuensis f. albiflora. Their structures were elucidated by spectroscopic methods.     

Condensed aromatics—XXIII. Cyclo[d.e.d.e.d.e.d.e.d.e.d.e]dodecakisbenzene (kekulene)

Some topological properties of coronoids are given. These systems have chemical counterparts in cycloarenes. For one of these molecules, viz. C₄₈H₂₄ kekulene, the simple Hückel molecular orbital analysis has been performed and employed in the construction of a harmonic force field. Finally the set of calculated vibrational frequencies is reported.     

Condensed aromatics—XXIV. Cyclo[d.e.d.e.e.d.e.d.e.e]decakisbenzene

The macrocyclic condensed aromatic hydrocarbon C₄₀H₂₀ cyclo[d.e.d.e.e.d.e.d.e.e] decakisbenzene is treated. It belongs to the class of cycloarenes. The simple Hückel molecular orbital analysis has been performed and employed in the construction of a harmonic force field. The set of calculated vibrational frequencies is reported.     

Heterometallic Carboxylate Complexes as Precursors for Mixed Oxides: III. 3d–4f Carboxylates

Russian Journal of General Chemistry - The current status of research into the thermal behavior of heterometallic 3d–4f carboxylates that are suitable candidates for single-source precursors...     

Biosynthesis of -p-hydroxyphenylglycine, a non-proteinogenic amino acid constituent of peptide antibiotics

Background: The non-proteinogenic amino acid p-hydroxyphenylglycine is a crucial component of certain peptidic natural products synthesized by a non-ribosomal peptide synthetase mechanism. In particular, for the vancomycin group of antibiotics p-hydroxyphenylglycine plays a structural role in formation of the rigid conformation of the central heptapeptide aglycone in addition to being the site of glycosylation. Initial labeling studies suggested tyrosine was a precursor of p-hydroxyphenylglycine but the specific steps in p-hydroxyphenylglycine biosynthesis remained unknown. Recently, the sequencing of the chloroeremomycin gene cluster from Amycolatopsis orientalis gave new insights into the biosynthetic pathway and allowed for the prediction of a four enzyme pathway leading to -p-hydroxyphenylglycine from the common metabolite prephenate.Results: We have characterized three of the four proposed enzymes of the -p-hydroxyphenylglycine biosynthetic pathway. The three enzymes are encoded by open reading frames (ORFs) 21, 22 and 17 (ORF21: [PCZA361.1, O52791, CAA11761]; ORF22: [PCZA361.2, O52792, CAA11762]; ORF17: [PCZA361.25, O52815, CAA11790]), of the chloroeremomycin biosynthetic gene cluster and we show they have p-hydroxymandelate synthase, p-hydroxymandelate oxidase and -p-hydroxyphenylglycine transaminase activities, respectively.Conclusions: The -p-hydroxyphenylglycine biosynthetic pathway shown here is proposed to be the paradigm for how this non-proteinogenic amino acid is synthesized by microorganisms incorporating it into peptidic natural products. This conclusion is supported by the finding of homologs for the four -p-hydroxyphenylpyruvate biosynthetic enzymes in four organisms known to synthesize peptidic natural products that contain p-hydroxyphenylglycine. Three of the enzymes are proposed to function in a cyclic manner in vivo with -tyrosine being both the amino donor for -p-hydroxyphenylglycine and a source of p-hydroxyphenylpyruvate, an intermediate in the biosynthetic pathway.     

A New Alchemical Poem Attributed to Khālid b. Yazīd (d. ca. 705)

This paper deals primarily with the identification of an inaccurately catalogued alchemical poem attributed to the famous Umayyad prince Khālid b. Yazīd (d. 705), edited, translated, and commented upon here for the first time. The paper also addresses the authenticity of Khālid’s interest in alchemy and connects that interest to the need of the early Islamic empire to develop its own gold coinage as a sign of political independence from Byzantine coinage that was up till then the currency of the lands occupied by early Muslims in the regions of modern-day Egypt and Syria. On the matter of the legendry character of Khālid which was apparently started by Ibn Khaldun and passed on after him to most nineteenth-century and early twentieth-century orientalists, the paper exposes here the inner contradictions in Ibn Khaldun’s theorising on the matter, and his failure to understand why someone like the historical Prince Khālid would be interested in alchemy.     

l-Galactose as a natural product: isolation from a marine octocoral of the first α-l-galactosyl saponin

Saponine 1 (6′-O-acetyl-3β-pregna-5,20-dienyl-α-l-galactopyranoside), that contains a l-galactose moiety linked to the aglycone through an infrequent α-glycosidic bond, has been isolated from the marine octocoral Muricea c.f. purpurea. This constitutes the first report on the occurrence of l-Gal as a nonpolymeric natural product. A CD procedure for the absolute stereochemical assignment of saponins, based on the CD analysis of its perbenzoylated derivative, is proposed.     

High-pressure study of a 3d–4f heterometallic CuEu–organic skeleton

We prepared a 3d–4f heterobimetallic CuEu–organic framework NBU-8 with a density of 1921 kg m⁻³ belonging to the family of dense packing materials (dense metal–organic frameworks or MOFs). This MOF material was prepared from 4-(pyrimidin-5-yl)benzoic acid (HPBA) with a bifunctional ligand site as a tripodal ligand and Cu²⁺ and Eu³⁺ as the metal centres; the molecular formula is Cu₃Eu₂(PBA)₆(NO₃)₆·H₂O. This material is a very promising dimethylformamide (DMF) molecular chemical sensor. Systematic high-pressure studies of NBU-8 were carried out by powder X-ray diffraction, high-pressure X-ray diffraction and molecular dynamics simulation. The high-pressure experiment shows that the (006) diffraction peak of the crystal structure moves toward a low angle with increasing pressure, accompanied by the phenomenon that the d-spacing increases, and as the pressure increases, the (10) diffraction peak moves to a higher angle, the amplitude of the d-spacing is significantly reduced and finally merges with the (006) diffraction peak into one peak. The amplitude of the d-spacing is significantly reduced, indicating that NBU-8 compresses and deforms along the a-axis direction when subjected to uniform pressure. This is caused by tilting of the ligands to become more vertical along the c direction, leading to its expansion. This allows greater contraction along the a direction. We also carried out a Rietveld structure refinement and a Birch–Murnaghan solid-state equation fitting for the high-pressure experimental results. We calculated the bulk modulus of the material to be 45.68 GPa, which is consistent with the calculated results. The framework is among the most rigid MOFs reported to date, exceeding that of Cu–BTC. Molecular dynamics simulations estimated that the mechanical energy absorbed by the system when pressurized to 5.128 GPa was 249.261 kcal mol⁻¹. The present work will provide fresh ideas for the study of mechanical energy in other materials.     

Molekulare Mechanismen für hydrolytische Enzymwirkung. 3. Mitt.: Ein allgemeiner Mechanismus für die Inhibierung von Acetylcholinesterase

Ohne Zusammenfassung     

A series of 3d–4f heterometallic MOFs: syntheses,structures, optical,and electrochemical properties

Abstract

A series of heterometallic metal-organic frameworks (MOFs) employing pyridine-2,6-dicarboxylate and 1,10-phenanthroline as ligands have been synthesized hydrothermally. In isostructural compounds 1–3 [Ln(pydc)₃Cu₂(phen)₄]·I·× H₂O (Ln?=?La (1), Nd (2), Dy (3); x?=?6, 5, 5), the metalloligand [Ln(pydc)₃] assembles with [Cu(phen)₂] units to construct a dodecanuclear cluster via Cu–O bonds and π–π interactions. The clusters are further stacked into three-dimensional supramolecular frameworks with nano-sized cavities. In [La(Hpydc)(pydc)₂Zn(phen)₃]·3H₂O (4), the metalloligand [Ln(Hpydc)(pydc)₂] assembles with [Zn(phen)₃] units to construct a tetranuclear cluster via electrostatic interaction and π–π interaction. This work reveals that the changes of lanthanide metalloligands and the coordination pattern of 3d transition centers would result in significant variation in the final structures. The thermal, optical, and electrochemical properties have been well investigated.     

Combined two-photon excitation and d → f energy-transfer in Ir/lanthanide dyads with time-gated selection from a two-component emission spectrum

In a pair of Ir/Eu and Ir/Tb dyads, two-photon excitation of the Ir-phenylpyridine chromophore at 780 nm is followed by partial d → f energy-transfer to give a combination of short-lived Ir-based (blue) and long-lived lanthanide-based (red or green) emission; these components can be selected separately by time-gated detection.     

Selective synthesis of oxazoles and pyrazines from α-bromo-1-phenylethanone using a by-product-promoted strategy

Oxazoles and pyrazines are fundamental heterocycles that widely found in natural products or drugs. In this work, a selective strategy for oxazoles and pyrazines synthesis using α-bromo-1-phenylethanone and ammonium acetate as starting materials was reported. This methodology features mild reaction conditions, readily accessible starting materials and good chemoselectivity. Mechanistic study indicates that this reaction involves a by-product-promoted (BPP) process for the formation of oxazole, that is, the in-situ formed hydrogen bromide (HBr) during the reaction promotes the whole tandem process.