Synthesis of an Optically Active Trisubstituted α,β-Butenolide, (S)-4, 6-Dihydroxy-2, 3-dimethyl-2-hexesoic Acid 1, 4-Lactone,from 2-Deoxy-D-ribose

The title compound has been synthesized efficiently from 2-deoxy-D-ribose. The synthesis involves : 1) an aldol like carbon-carbcr. bond formation of (S)-3, 5-dibenzyioxy-2-pentanor.e (8) with a lithium enolate of methyl propanoate, and 2) O-de-benzylation of the aldol adducts (11) for a γ-lactonization followed by β-elimination of the desired butenolide skeleton.     

Synthesis of an Enkephalin Analogue Containing an α,α-Disubstituted Heterocyclic Aminophosphonic Acid

Abstract

Synthesis of a phosphonopentapeptide enkephalin analogue was achieved from heterocyclic aminophosphonates via the coupling of Boc-Tyr-Gly-Gly-OH with phosphonodipeptide. The latter was formed by coupling Boc-Phe-OH with N-terminal α,α-disubstituted heterocyclic α-aminophosphonates.

GRAPHICAL ABSTRACT      

Acetylene-allene rearrangement of propargyl systems X—CH2—C≡CH (X = H,Me, NMe2, OMe,F, SMe): an ab initio study

Acetylene—allene rearrangement in propargyl systems XCH₂CHCH (X = H, Me, NMe₂, OMe, F, and SMe) was studied using the ab initio approach. The relative stabilities of the starting and final propyne structures and the corresponding allenes as well as the structure of intermediate carbanions were considered. n--Conjugation was shown to dominate in allene stabilization while the inductive effect of heteroatomic substituents makes at least comparable contribution to stabilization (or destabilization) of the propynyl structure. In particular, relative instability of 1-methoxypropyne can be rationalized by high electronegativity of O atom, which leads to dramatic decrease in the total electron density in the region of the neighboring CC triple bond. The influence of substituents on the mobility of the migrating proton was considered for the gas phase and with solvation effects included. Calculations involving electron correlation at the MP2 level of theory were shown to be insufficient for correct reproduction of the energy differences between the corresponding propynes and allene structures. The results of MP4 calculations with inclusion of ZPE correction are in good agreement with the available experimental data.     

Enantioselective organocatalytic Michael addition of 2-arylacetates and 2-arylacetonitriles having an electron-withdrawing group to α,β-unsaturated aldehydes

The asymmetric organocatalytic Michael addition reaction of 2-arylacetates and 2-arylacetonitriles having an electron-withdrawing group to α,β-unsaturated aldehydes has been established using diphenylprolinol trimethylsilyl (TMS) ether as organocatalyst. The 2-arylacetates and 2-arylacetonitriles having NO₂-, CO₂Me-, and CN-functional groups on the aromatic ring can be used in this reaction. The desired products were obtained with good to excellent yields and high enantioselectivities (up to 97% ee).     

Diastereoselectivity switch in cooperatively catalyzed three-component reactions of an aryldiazoacetate, an alcohol, and a β,γ-unsaturated α-keto ester

A highly switchable,diastereoselectivity-controlled, three-component reaction of aryldiazoacetate, alcohol,and β,γ-unsaturated α-keto esters has been achieved through a dual-metal cooperative catalysis strategy.     

Zur Photosynthese grüner Pflanzen, 2. Mitt.: Massenspektroskopische Untersuchungen an Carotinoiden

Zusammenfassung Die Massenspektren der wichtigsten Strukturtypen von Carotinoiden werden auf ihre charakteristische Fragmentierung untersucht und Zerfallsmechanismen an Hand von exakten Massenmessungen und Markierungsversuchen diskutiert.

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Photosynthesis in green plants II: Mass spectrometric investigation of carotinoids

The characteristic fragmentation of the most important structural types of carotinoids is investigated and fragmentation mechanisms are discussed on the basis of exact mass measurements and labelling experiments.

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Mit 22 Abbildungen

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1. Mitt.:H. Budzikiewicz, H. Eckau undH. H. Inhoffen, Z. Naturforsch.24b, 1147 (1969).     

Gas chromatography–mass spectrometry screening methods for select UV filters,synthetic musks,alkylphenols, an antimicrobial agent,and an insect repellent in fish

Two screening methods have been developed for simultaneous determination of ten extensively used personal care products (PCPs) and two alkylphenol surfactants in fish. The methods consisted of extraction, clean-up, derivatization and analysis by gas chromatography–mass spectrometry with selected ion monitoring (GC–SIM–MS) or gas chromatography–tandem mass spectrometry (GC–MS/MS) techniques. Among solvents tested to assess recovery of target compounds from 1-g tissue homogenates, acetone was selected as optimal for extracting compounds with dissimilar physicochemical properties from fish tissue. Initial experiments confirmed that GC–SIM–MS could be applied for analysis of lean fillet tissue (<1% lipid) without gel-permeation chromatography (GPC), and this approach was applied to assess the presence of target analytes in fish fillets collected from a regional effluent-dominated stream in Texas, USA. Benzophenone, galaxolide, tonalide, and triclosan were detected in 11 of 11 environmental samples at concentrations ranging from; 37 to 90, 234 to 970, 26 to 97, and 17 to 31 ng/g, respectively. However, performance of this analytical approach declined appreciably with increasing lipid content of analyzed tissues. Successful analysis of samples with increased lipid content was enabled by adding GPC to the sample preparation protocol and monitoring analytes with tandem mass spectrometry. Both analytical approaches were validated using fortified fillet tissue collected from locations expected to be minimally impacted by anthropogenic influences. Average analyte recoveries ranged from 87% to 114% with RSDs <11% and from 54% to 107% with RSDs <20% for fish tissue containing <1% and 4.9% lipid, respectively. Statistically derived method detection limits (MDLs) for GC–SIM–MS and GC–MS/MS methodologies ranged from 2.4 to 16 ng/g, and 5.1 to 397 ng/g, respectively.     

Spektroskopische Untersuchungen an organischen Carbonylverbindungen, 10. Mitt.: Vergleichende Absorptions-, Fluoreszenz- und NMR-Messungen an ausgewählten β-Diketonen und ihren BF2- und Be-Komplexen

Summary Be complexes of selected styryl-substituted -diketones were prepared and their absorption, fluorescence, and NMR spectra were measured. The data of these compounds are presented and compared with those of the analogous free ligands and their BF₂-complexes.

     

Structure, electronic configuration, and Mössbauer spectral parameters of an antiferromagnetic Fe2-peroxo intermediate of methane monooxygenase

Determining structures of reaction intermediates is crucial for understanding catalytic cycles of metalloenzymes. However, short life times or experimental difficulties have prevented obtaining such structures for many enzymes of interest. We report geometric and electronic structures of a peroxo intermediate in the catalytic cycle of methane monooxygenase hydroxylase (MMOH) for which there is no crystallographic characterization. The structure was predicted via spin density functional theory using (57)Fe M?ssbauer spectral parameters as a reference. Computed isomer shifts (δ(Fe) = +0.68, +0.66 mm s(-1)) and quadrupole splittings (ΔE(Q) = -1.49, -1.48 mm s(-1)) for the predicted structure are in excellent agreement with experimental values of a peroxo MMOH intermediate. Predicted peroxo to iron charge transfer bands agree with UV-Vis spectroscopy. Peroxide binds in a cis μ-1,2 fashion and plays a dominant role in the active site's electronic structure. This induces a ferromagnetic to antiferromagnetic transition of the diiron core weakening the O-O bond in preparation for cleavage in subsequent steps of the catalytic cycle.     

Supra-supra, supra-antara, and stepwise-diradical pathways for an observed 16-electron double-[4 + 4] cycloaddition within metal-templated dialkyne dimers (PtX2)2(μ-R2PCCCCPR2)2

Quantum chemistry calculations are used to provide insight into the cycloaddition of two dialkyne chains in initially monocyclic organoplatinum dimers of the type (PtX(2))(2)(μ-R(2)PC(4)PR(2))(2), where X = Cl or Me and R = Ph or Me. Previous experimental studies showed that the cycloaddition occurs with {X, R} = {Cl, Ph} but not {Me, Ph}. Two concerted pericyclic paths, a D(2h)-symmetry double-[π4s+π4s] "Hu?ckel path" and a D(2)-symmetry double-[π4s+π4a] "Mo?bius path", were explored via orbital energy correlation diagrams (OECDs) computed using a singly occupied molecular orbital technique developed earlier. In accord with pericyclic reaction theory, the 16e(-) rearrangement is forbidden along the D(2h) Hu?ckel path; four electrons would need to change their orbital symmetries. The D(2) Mo?bius path, afforded by the natural twist in the reactant structure which allows the desired Mo?bius orbital connectivity for a 4n rearrangement, is concluded to be a borderline forbidden pathway. This Mo?bius path creates avoided crossings in the OECD, which allows consistent orbital populations throughout the reaction, but it does not cause a change in intended orbital correlation, and the predicted activation barrier is rather high (～50 kcal mol(-1)). The avoided crossings show strong coupling, but a clear HOMO-LUMO gap for the reaction is not produced. A stepwise path is also presented, with evidence of its diradical character.     

Formate dehydrogenase–viologen-immobilized electrode for CO2 conversion,for development of an artificial photosynthesis system

Formate dehydrogenase (FDH)–viologen with a long alkyl chain (CH₃V(CH₂) _n COOH) immobilized on an indium–tin oxide (ITO) electrode, with the function of reduction of CO₂ to formic acid, was investigated as an artificial photosynthesis device based on CO₂ reduction. The amount of formic acid produced by use of FDH–CH₃V(CH₂) _n COOH immobilized on ITO in CO₂-saturated buffer solution, on application of a potential, as a result of one-electron reduction of viologen, depends on the carbon chain length of CH₃V(CH₂) _n COOH. When a CH₃V(CH₂)₉COOH–FDH/ITO electrode was used, production of formic acid was estimated to be 23 μmol after 3 h.     

Vergleichende dielektrische und Ultraschall-Messungen bei 2 · 106 Hz an Polyvinylestern,Polyacrylestern und Polyvinyläthern

Ohne Zusammenfassung Unseren Kollegen K. Schmieder und F. Würstlin danken wir für interessante Diskussionen und für die Mitteilung teilweise noch unver?ffentlichter Me?ergebnisse. Für die überlassung der untersuchten Substanzen sind wir K. Herrle, K. Holzer, W. Nieswandt und P. Siebel zu besonderem Dank verpflichtet.     

Volumen-, Temperatur- und Intensit?tsmessungen an Knallgasflammen

Ohne ZusammenfassungVortrag, gehalten auf der Tagung der Gesellschaft Deutscher Chemiker, Fachgruppe Analytische Chemie am 25. Oktober 1958 in Marburg (Lahn).Dissertation, Chemisches Institut der Universität Bonn.     

ICP-AES法测定石灰石、白云石中的Al_2O_3,CaO,TFe_2O_3,MgO,MnO,SiO_2,TiO_2

采用无水碳酸钾+硼酸处理样品,电感耦合等离子体发射光谱法同时测定石灰石及白云石中7种组分,筛选了不同仪器参数条件,对各组分分别选用2条相对谱线强度适中的谱线进行分析,并以元素平均值的模式输出数据结果,测定的相对标准偏差小于0.60%.经对国家一级石灰石及白云石标准物质分析验证,结果与标准值吻合.     

Synthesis of Anhydronectriachrysone,an Extensively Conjugated γ-Pyrone

The synthesis of anhydronectriachrysone (2) through the DIBAH reduction of toralactone (3), followed by dehydration of the corresponding lactol (4) is reported (38% yield).     

Dielektrische Messungen an bituminösen Stoffen,III

Zusammenfassung Für die in vorstehendem Abschnitt beschriebenen großtechnisch hergestellten Steinkohlenteerpeche läßt sich die Brauchbarkeit dielektrischer Untersuchungen dahin formulieren, daß die Bestimmung des Absolutwertes der Dielektrizitätskonstante der Mischungskomponenten und die Lagebestimmung des Gebietes anomaler Dispersion Voraussagen über den Lösungs- bzw. Quellungszustand der erhaltenen Weichpeche und über ihr Verhalten bei mechanischer Deformation ermöglicht. Die bei den Teersonderpechen festgestellte Verschiebung des Dispersionsgebietes nach tiefen Temperaturen eröffnet aber auch Ausblicke auf weitere Auswertungsmöglichkeiten dielektrischer Messungen bei der Erforschung der für die Verarbeitung und den Bestand bituminöser Schutzfilme gleichwichtigen Benetzungs-, Verdrängungs- und Adhäsionserscheinungen. Es ist bekannt, wie sehr z. B. die Benetzung von Grenzflächen nicht nur durch die chemische Zusammensetzung, sondern vor allem durch die Konfiguration der Moleküle der benetzenden Flüssigkeit und damit ihre Ladungsverteilung gelenkt wird. Es erscheint deshalb wahrscheinlich, daß eine bei Einwirkung eines elektrischen Wechselfeldes erkennbare stärkere Molekülbeweglichkeit auch bei tieferen Temperaturen, wie sie sich aus der Lage des Dispersionsgebietes ergibt, sich auch bei Situationen und Vorgängen günstig bemerkbar machen muß, die mit der für die Wirksamkeit eines Schutzfilms so wesentlichen Eigenschaft der Adhäsion zusammenhängen.Die Durchrechnungsbeziehungen zwischen Dielektrizitätskonstante und absoluter Viskosität ergab bei allen untersuchten Steinkohlenteeren und-pechen bei niedrigen und mittleren Viskositäten einen einfachen quantitativen Zusammenhang.     

An unexpected synthesis of an α,β,γ,δ-unsaturated ketone due to an abnormal opening of benzylidene acetal by bromide anion

An unexpected synthesis of an α, β, γ,δ-unsaturated ketone, which embodies a new type of oxy-carbon cyclic structure, was achieved, while we tried to construct the taxane CB-ring system. Also, a series of abnormal reaction phenomena was found to be related to the formation and reaction of seven membered cyclic benzylidene acetal.