Microbial Transformation of Taxoids and Synthesis of Taxoids ith an Oxetane Ring

SincethediscoveryofanhcanceragentPaclitaxel(Taxol@),'studiesonTaxUsSPecieshaVebroughtmorethantwohundrednewtaxoidsintothetaxanediterpenoidfaIYuly.'Recently,Zap-DeacetoxytaxinineJ1andsomeofitsanalogswereisolatedinhighamountsfromTaxusyUnnanensisandotherTaresspecies.2Itseemsthat1anditsanalogscanbeusedasstaltingmaterialsforthechemoenZylnaticSynthesisofpaclitaXelanalogs,aswellasvaluableforthestudyofthebiosynthesisoftaxoidsinToosspecies.MicrobialenZymaticSystemsmayserveasPOwerfultoolstOndnd…     

Isolation and Structure of Pseurotin A,a Microbial Metabolite of Pseudeurotium ovalis STOLK with an Unusual Heterospirocyclic System

The structure and absolute configuration of pseurotin A, a new metabolite, isolated from culture filtrates of Pseudeurotium ovalis STOLK (Ascomycetes) has been shown to be (1′S, 2′S, 5S, 8S, 9R, 3′Z)-8-benzoyl-2 (1′,2-dihydroxy-3′-hexenyl)-9-hydroxy-8-methoxy-3-methyl-1-oxa-7-azaspiro [4,4]non-2-ene-4,6-dione ( 1 ).     

Transformation of methyl N-methyl-N-(6-substituted-5-nitro-4-pyrimidinyl)aminoacetates into 4-methylamino-5-nitrosopyrimidines and 9-methylpurin-8-ones

N-Methyl-N-(6-substituted-5-nitro-4-pyrimidinyl)aminoacetic acid methyl esters under the treatment of sodium alkoxides, depending on the nature of substituents in 6 position of the pyrimidine ring, undergo ring closure and rearrangement to give 6-substituted-4-methylamino-5-nitrosopyrimidines or 9-methylpurin-8-ones.     

Rhodauricanol A,an analgesic diterpenoid with an unprecedented 5/6/5/7 tetracyclic system featuring a unique 16-oxa-tetracyclo[11.2.1.01,5.07,13]hexadecane core from Rhododendron dauricum

A novel diterpenoid with an unprecedented 5/6/5/7 tetracyclic system, rhodauricanol A (1), five new grayanane-derived diterpenoids, dauricanols A?E (2?6), and five known ones (7?11) were isolated from the flowers of Rhododendron dauricum. Rhodauricanol A (1) possesses a unique 5/6/5/7 tetracyclic ring system featuring a 16-oxa-tetracyclo[11.2.1.0^1,5.0^7,13]hexadecane core. Dauricanols A?C (2?4) are the first 1,3-dioxolane conjugates of grayanane diterpenoids and 5-hydroxymethylfurfural and vanillin, respectively, and dauricanols D (5) and E (6) represent the first examples of 6-deoxy-1,5-seco-grayanane diterpenoids. Their structures were determined by spectroscopic methods, quantum chemical calculation including ¹³C NMR-DP4+ analysis and ECD calculation, and single-crystal X-ray diffraction analysis. Plausible biosynthetic pathways for 1?4 were proposed. All the isolates showed significant analgesic activities, and dauricanols B (3) and C (4) showed more potent analgesic activities than the positive control, morphine.     

A5InPb8 (A = K, Rb): an apparent zintl phase with lead tetrahedra interbridged by mu6-In atoms

Reaction of elemental In, Pb, and K, or Rb within welded Ta containers at 900 degrees C followed by subsequent annealing at 350 degrees C gives the new phases A5InPb8 (A = K, Rb). These crystallize in the trigonal space group R3m (No. 166, Z = 3) with cell dimensions of a = 6.8835(6) and 6.885(1) A and c = 37.591(5) and 37.64(2) A for K5InPb8 and Rb5InPb8, respectively. The structure contains clusters built of pairs of Pb4 tetrahedra that are interbridged by a mu6-In atom. The InPb8 units, which in the isolated case would behave as ideal 40-electron Wade's rule clusters, are weakly interlinked into sheets in the ab plane by long (3.5 A) intercluster Pb-Pb interactions. According to the EHTB calculations, these cause a broadening of the valence band and thus generate a number of new states at the Fermi level. Compound K5InPb8 is metallic (rho298 approximately 42 microohms cm, (delta rho/delta T)/rho approximately 1.4(2) x 10(-1) K(-1)) which is in agreement with the expectations according to calculations on the anion network.     

Construction of 5-(Alkylamino)-6-aryl/alkylpyrazine-2,3-dicarbonitriles via the One-Pot Reaction of Alkyl Isocyanides with Aryl/Alkyl Carbonyl Chlorides and Diaminomaleonitrile: Fluorescence and Antimicrobial Activity Evaluation

5-(Alkylamino)-6-aryl/alkylpyrazine-2,3-dicarbonitriles were successfully synthesized in good to moderate yields by reacting alkyl isocyanides with aryl/alkyl carbonyl chlorides, followed by the addition of diaminomaleonitrile. The synthesized pyrazines were fully characterized in this investigation, and X-ray crystal structure analysis was performed on some derivatives. The antibacterial and antifungal activities of the newly synthesized pyrazine-2,3-dicarbonitriles were assessed in addition to their UV and fluorescence results. All the compounds showed similar UV–Vis spectral features with absorption peaks (λ_max) around 267, 303, and 373 nm.     

一种获得高活性和高稳定性甲烷无氧芳构化Mo/HZSM-5催化剂的前处理方法

 利用氢气在较低温度(623 K)下对6%Mo/HZSM-5催化剂进行预处理,考察了经低温还原预处理的催化剂在甲烷无氧芳构化反应中的催化性能. 结果表明,经过预处理的催化剂比未经预处理的催化剂表现出更好的甲烷转化活性和稳定性. 1H MAS NMR和EPR表征结果表明,在623 K氢气气氛中对Mo/HZSM-5催化剂进行预处理不会造成Mo物种在分子筛外表面的进一步分散,也不会导致外表面的Mo物种向孔道内迁移. 但是,低温还原预处理可以有效地促进Mo物种由易还原的六方密堆积结构向难还原的面心立方结构转化,后者在反应中具有更好的活性和稳定性.     

Ca5Cl3(C2)(CBC): A Compound with a Layer Structure and an Unusual Anion Combination

Allene homologous cumulenes are not always linear! The title compound, which has now been synthesized and structurally characterized, contains a BC₂ unit that is isoelectronic with CO₂ and that deviates by 16° from linearity without losing the double-bond character of the B–C bonds. The BC₂ unit is located in the center of a bicapped trigonal prism of calcium ions (see picture).     

A New Way to Obtain Mo/HZSM-5 Catalyst with High Activity and Selectivity for Methane Dehydro-aromatization 一种制备高活性和高稳定性甲烷无氧芳构化Mo/HZSM-5的新方法

 采用气相化学沉积法对HZSM-5分子筛的外表面进行选择性修饰,然后将它作为载体制备Mo/HZSM-5 催化剂,并应用于甲烷无氧脱氢芳构化反应. 改性的催化剂比未改性的催化剂表现出更好的甲烷转化活性、芳烃选择性和稳定性,明显地抑制了积碳的生成. 利用核磁氢谱对催化剂进行了表征. 在未经改性的Mo/HZSM-5催化剂表面,平均每个晶胞中含有1.12个B酸中心, 而在改性后的催化剂表面,平均每个晶胞中只有0.61个B酸位. 说明在甲烷无氧芳构化反应中,少量的B酸中心即可达到反应要求,过多的酸性位只会导致更多积碳物种的生成,从而加快催化剂失活速度,降低其稳定性.     

Heterometallic clusters with the {MoNbI8} core: The synthesis and crystal structures of (Ph4P)2[Mo5NbI8Cl6] and (4-MePyH)5[Mo5NbI8Cl6]Cl2

Heterometallic chloride complexes [Mo₅NbI₈Cl₆] ⁿ⁻ (n = 2, 3) are synthesized. The crystal structures of their salts are determined: for (Ph₄P)₂[Mo₅NbI₈Cl₆] (I), triclinic crystal system, spacegroup P [`1]\bar 1, a = 10.9886(6), b = 11.4604(5), c = 13.4343(7) ?, α = 66.124(2), β = 86.892(2), γ = 86.490(2)°, Z = 1, V = 1543.35(13) ?³; and for (4-MePyH)₅[Mo₅NbI₈Cl₆]Cl₂ (II), monoclinic crystal system, space group C2/m, a = 16.4937(4), b = 14.7335(3), c = 11.6534(3) ?, β = 99.8750(10)°, Z = 2, V = 2789.94(11) ? The geometric parameters of compounds I and II and the conditions for the formation of the complexes with the charges −2 and −3 are discussed.     

A Blocking Group Scan Using a Spherical Organometallic Complex Identifies an Unprecedented Binding Mode with Potent Activity In Vitro and In Vivo for the Opioid Peptide Dermorphin

Herein, the selective enforcement of one particular receptor‐ligand interaction between specific domains of the μ‐selective opioid peptide dermorphin and the μ opioid receptor is presented. For this, a blocking group scan is described which exploits the steric demand of a bis(quinolinylmethyl)amine rhenium(I) tricarbonyl complex conjugated to a number of different, strategically chosen positions of dermorphin. The prepared peptide conjugates lead to the discovery of two different binding modes: An expected N‐terminal binding mode corresponds to the established view of opioid peptide binding, whereas an unexpected C‐terminal binding mode is newly discovered. Surprisingly, both binding modes provide high affinity and agonistic activity at the μ opioid receptor in vitro. Furthermore, the unprecedented C‐terminal binding mode shows potent dose‐dependent antinociception in vivo. Finally, in silico docking studies support receptor activation by both dermorphin binding modes and suggest a biological relevance for dermorphin itself. Relevant ligand‐protein interactions are similar for both binding modes, which is in line with previous protein mutation studies.     

Concise Synthesis of a Pateamine A Analogue with In Vivo Anticancer Activity Based on an Iron‐Catalyzed Pyrone Ring Opening/Cross‐Coupling

The marine macrolide pateamine A and its non‐natural sibling DMDA‐Pat A are potent translation inhibitors targeting the eukaryotic initiation factor 4A (eIF4A), an enzyme with RNA helicase activity. Although essential for every living cell, this protein target seems “drugable” since DMDA‐Pat A has previously been shown to exhibit remarkable in vivo activity against two different melanoma mouse models. The novel entry into this promising compound presented herein is shorter and significantly more productive than the literature route. Key to success was the masking of the signature Z,E‐configured dienoate subunit of DMDA‐Pat A in the form of a 2‐pyrone ring, which was best crafted by a gold‐catalyzed cyclization. While the robustness of the heterocycle facilitated the entire assembly stage, the highly isomerization‐prone seco‐Z,E‐dienoic acid could be unlocked in due time for macrolactonization by an unconventional iron‐catalyzed ring opening/cross coupling. Moreover, the crystal structure analysis of an advanced intermediate gave first insights into the conformation of the macrodilactone framework of the pateamine family, which is thought to be critical for eliciting the desired biological response.     

Syntesis and Crystal Structure of Cs2Nb6Br5F12: A Nb6 Cluster Compound with a One-Dimensional Nb6Br5F7F6 Unit Connection

The synthesis and the crystal structure of Cs₂Nb₆Br₅F₁₂ containing octahedral niobium clusters are presented in this work. This bromofluoride is based on a Nb₆Lⁱ₁₂F^a₆ (L=Br and F) unit and crystallizes in the orthorhombic system (space group, Cccm; Z=4; a=9.2446(2) Å, b=13.6256(3) Å, and c=17.1665(4) Å; R=0.0241). Fluorine and bromine are randomly distributed on the inner ligand positions, Lⁱ, that edge-bridge the Nb₆ cluster whereas fluorine fully occupies the apical positions (L^a). The units are linked to each other by apical ligands leading to an original one-dimensional unit connection. The cesium atoms are statistically distributed on several sites that describe parallel channels along the [1 0 0] direction. The influence of fluorine ligands upon the stabilization of this structure type as well as the structural relationships with Ba₂Zr₆Cl₁₇(B), Nb₆F₁₅, and NaMo₆Cl₁₃ will be evidenced and discussed.     

A Supramolecular Photosensitizer System Based on Nano-Cu/ZIF-8 Capped with Water-Soluble Pillar[6]arene and Methylene Blue Host–Guest Complexations

Photodynamic therapy (PDT) as a safe, non-invasive modality for cancer therapy, in which the low oxygen and high glutathione in the tumor microenvironment reduces therapeutic efficiency. In order to overcome these problems, we prepared a supramolecular photosensitive system of O₂-Cu/ZIF-8@ZIF-8@WP6–MB (OCZWM), which was loaded with oxygen to increase the oxygen concentration in the tumor microenvironment, and the Cu²⁺ in the system reacted with glutathione (GSH) to reduce the GSH concentration to generate Cu⁺. It is worth noting that the generated Cu⁺ can produce the Fenton reaction, thus realizing the combination therapy of PDT and chemodynamic therapy (CDT) to achieve the purpose of significantly improving the anti-cancer efficiency.     

A simple compound with an ­unexpectedly complex structure: 4‐pyridone 6/5‐hydrate

The crystal structure of the title compound, C₅H₅NO·H₂O, contains five independent mol­ecules of pyridone and six independent water mol­ecules. The space group is P2₁, but four of the pyridones and four waters correspond closely to P2₁/n. The packing involves two layers; one consists of head‐to‐tail chains of pyridone mol­ecules 1–4 linked by N—H?O hydrogen bonds, and a second layer involves all the waters and the fifth pyridone. The layers are linked by hydrogen bonds from water to pyridone oxy­gen. The four water O atoms that accept only one classical hydrogen bond have their environment completed by C—H?O interactions.     

A widely varying range of products in reactions of C6F5BrF2, C6F5IF2, and C6F5IF4 with Lewis acids of different strength

The relative fluoride donor ability: C₆F₅BrF₂ > C₆F₅IF₂ > C₆F₅IF₄ was outlined from reactions with Lewis acids of graduated strength in different solvents. Fluoride abstraction from C₆F₅HalF₂ with BF₃·NCCH₃ in acetonitrile (donor solvent) led to [C₆F₅HalF·(NCCH₃)_n][BF₄]. The attempted generation of [C₆F₅BrF]⁺ from C₆F₅BrF₂ and anhydrous HF or BF₃ in weakly coordinating SO₂ClF gave C₆F₅Br besides bromoperfluorocycloalkenes C₆BrF₇ and 1-BrC₆F₉. In reactions of C₆F₅IF₂ with SbF₅ in SO₂ClF the primary observed intermediate (¹⁹F NMR, below 0 °C) was the 4-iodo-1,1,2,3,5,6-hexafluorobenzenium cation, which converted into C₆F₅I and 1-IC₆F₉ at 20 °C. The reaction of C₆F₅IF₄ with SbF₅ in SO₂ClF below −20 °C gave the cation [C₆F₅IF₃]⁺ which decomposed at 20 °C to C₆F₅I, 1-iodoperfluorocyclohexene, and iodoperfluorocyclohexane. Principally, the related perfluoroalkyl compound C₆F₁₃IF₄ showed a different type of products in the fast reaction with AsF₅ in CCl₃F (−60 °C) which resulted in C₆F₁₄. Intermediate and final products of C₆F₅HalF_n−1 (n = 3, 5) with Lewis acids were characterized by NMR in solution. Stable solid products were isolated and analytically characterized.