bluuebunny/crossref_metadata_2025 huggingface dataset:
Postgraduate training opportunities for chiropractors: A description of United States programs
Authors: Schut Samuel M.
Published: January 2024

Objective

The objective of this study was to describe and compare the current postgraduate training opportunities (PTOs) in the United States (US) for which doctors of chiropractic are eligible, namely, residencies, fellowships, and board certifications.

Methods

An internet search of publicly available English-language websites on Google.com was executed using a cache-cleared private browser and key search phrases. Following webpage data extraction, e-mail and telephone follow-up were completed with officials from institutions offering doctor of chiropractic programs possessing accreditation by the Council on Chiropractic Education (CCE) in the US. Additional programs identified were annotated and incorporated into the data set if they met the inclusion criteria. Descriptive statistics were generated following data aggregation.

Results

Three-hundred internet search results were screened, 70 of which were assessed for eligibility and 47 included for descriptive analysis. Among the 16 CCE-accredited institutions solicited, 13 returned correspondence (81.3% response rate), resulting in the addition of 2 programs to the data set ascertained by the initial web search. There were 49 PTOs for chiropractors. Of programs available, residencies represented 49.0% (24/49) of programs, and fellowships represented 12.2% (6/49) of programs. There were 19 board specialty diplomate programs, constituting 38.8% of PTOs.

Conclusion

This work details preliminary descriptive information on the current state of US-based PTOs for chiropractors.
Chemie und Biologie natürlicher Diels‐Alder‐Reaktionen
Authors: Stocking Emily M. , Williams Robert M.
Published: July 2003

Seit kurzem ist bekannt, dass Diels‐Alder‐Cycloadditionen zum Reaktionsrepertoir lebender Systeme gehören. Es gibt auch Anzeichen für eine vermittelnde Wirkung von Enzymen in Diels‐Alder‐Reaktionen bei der Biosynthese von Sekundärmetaboliten. 2002 jährte sich der Geburtstag von Alder zum 100. Mal und waren 75 Jahre seit der Entdeckung der Diels‐Alder‐Reaktion vergangen. Es scheint, als ob lebende Systeme schon vor Äonen diese überaus vielseitige und nützliche Ringschlussreaktion entdeckt hätten und seitdem zum Aufbau komplexer Naturstoffe nutzen. Wir geben hier einen Überblick über Naturstoffe verschiedener Verbindungsklassen (Polyketide, Isoprenoide, Phenylpropanoide, Alkaloide), bei deren Biosynthese eine Beteiligung von Diels‐Alder‐Reaktionen, katalysiert oder unkatalysiert, vermutet wird.
Richtlinien für die Wiedergabe von Pulssequenzen für die NMR‐Spektroskopie in Lösung
Authors: Berger Stefan , Zeller, Leipzig Uta
Published: July 2003

Während der Arbeit an der Spezifizierung eines Standards für die mehrdimensionale magnetische Resonanzspektroskopie (NMR‐Spektroskopie) wurde deutlich, dass die spektroskopischen Daten um Informationen über die experimentellen Bedingungen ergänzt werden müssen, besonders über die zur Beobachtung der Interferogramme oder Spektren verwendeten Pulssequenzen. Das Fehlen dieser Informationen behindert nicht nur häufig eine nachfolgende Behandlung mit Rechenprogrammen, sondern macht auch eine Interpretation des Endergebnisses nahezu unmöglich. Die hier niedergelegten Empfehlungen wurden in Zusammenarbeit mit NMR‐Geräteherstellern erarbeitet, um eine Übereinkunft über eine definierte Liste der am meisten genutzten Pulssequenz‐Programme zu erlangen. Die Liste enthält die Pulssequenzen, bei denen eine Einigung hinsichtlich des Akronyms für die Experimentbezeichnung und der wesentlichen instrumentenunabhängigen Parameter, die zu einer konsistenten Darstellung nötig sind, erzielt wurde. Mit ihr soll in keiner Weise die Freiheit der Hersteller oder Nutzer eingeschränkt werden, neuartige Pulssequenzen zu entwickeln, doch sie sollte bei der Darstellung experimenteller Daten helfen, wenn die gebräuchlicheren Sequenzen genutzt wurden.
Titelbild: Ein konjugierter molekularer Riesenring (Angew. Chem. 27/2003)
Authors: Mayor Marcel , Didschies Claudia
Published: July 2003

Als Rundlauf für Elektronen wurde ein Riesencyclus mit einer Peripherie aus konjugationsfähigen Einheiten entwickelt. Der Durchmesser dieses vermutlich größten formbeständigen und monodispersen Ringes beträgt 12 nm. Das Vorderrad eines Fahrrades stand mit seiner 16‐zähligen Symmetrie Modell beim Design des Moleküls. Synthese und Eigenschaften des Riesencyclus beschreiben M. Mayor und C. Didschies in ihrer Zuschrift auf S. 3284 ff.
Chemistry and Biology of Biosynthetic Diels–Alder Reactions
Authors: Stocking Emily M. , Williams Robert M.
Published: July 2003

Nature's repertoire of biosynthetic transformations has recently been recognized to include the Diels–Alder cycloaddition reaction. Evidence now exists that there are enzymes that mediate the Diels–Alder reaction in secondary metabolic biosynthetic pathways. 2002 marked the 100th anniversary of Alder's birth and 75 years since the discovery of the Diels–Alder reaction. It would appear that living systems discovered and made use of this ubiquitously useful ring‐forming reaction eons ago for the construction of complex natural products. In this Review an overview is given of all of the known classes of natural products (polyketides, isoprenoids, phenylpropanoids, alkaloids) that have been speculated to arise by a biological Diels–Alder reaction.
Gibt es den verständlichen Text? ‐ eine empirische Untersuchung zum Verstehen chemischer Texte
Authors: Schrader Claudia , Wolf Elke , Wenck Helmut
Published: July 2003

WER HAT DIESE ERFAHRUNG noch nicht gemacht? Man erzählt im Bekanntenkreis, dass man Chemie studiert hat und blickt in entgeisterte Gesichter. „Das Fach habe ich in der Schule noch nie verstanden”︁, ist dann oft die Antwort.

Ist Chemie wirklich so kompliziert oder schaffen die Lehrkräfte und Schulbücher es nicht, den Lehrstoff transparent zu gestalten? Sicherlich spielen beide Aspekte eine wichtige Rolle, doch soll in diesem Artikel nur auf die Kommunikationsproblematik eingegangen werden. Ein Großteil der Kommunikationsprobleme beruht auf der Fachsprache und auf dem kommunikativen Gefälle zwischen Lehrkräften und Schülerschaft. Das Sprachvermögen beeinflusst also das Lernen von Chemie. Becker et al. folgern daraus, dass der Verständlichkeit von Schulbuchtexten eine dominierende Bedeutung zukommt [1]. Doch was ist ein verständlicher Text?
Radierungen einmal anders
Authors: Vennemann Hendrik , Oetken Marco
Published: July 2003

ALBRECHT DÜRER, Rembrandt, Francisco José de Goya aber auch Künstler wie Pablo Picasso, Edvard Munch oder Horst Janssen haben sich um die Technik der Radierung bemüht, die sich seit ihrer Erfindung einer stetigen Beliebtheit erfreut. Selbst Goethe schätzte diese künstlerische Technik: Gott segne Kupfer, Stichel und Stift und Werkzeuge der Wiedergabe, so dass das Gute, das einmal vorhanden, in unzähligen Abbildern vor der Vergessenheit gerettet werden kann. [1]
Einfache Experimente zum Thema Glas
Authors: Wurm Dagmar , Woest Volker
Published: July 2003

DAS THEMA GLAS im Chemieunterricht ist nicht neu. In den letzten Jahren sind zahlreiche Veröffentlichungen mit Schulversuchen und Unterrichtsmaterialien erschienen [1‐3]. In dieser Arbeit werden neue einfache Versuche vorgestellt, die an der Universität Jena in enger Zusammenarbeit mit dem Otto‐Schott‐Institut für Glaschemie entwickelt wurden und die es erlauben, dass Thema Glas bereits im Anfangsunterricht und in der Regelschule anschaulich zu vermitteln. So soll ein Beitrag geleistet werden, dass dieser Alltagswerkstoff stärkeren Eingang in den Chemieunterricht findet.

Besonderes Augenmerk wurde dabei auf die Herstellung von kleinen Glassteinen gelegt. Der verwendete Rohstoff Natriummetaphosphat ist niedrigschmelzend und leichtflüssig, so dass sich gut zu verarbeitende Schmelzen ergeben. Auf den Zusatz toxischer Bleioxide kann verzichten werden.
Adolf Butenandt und sein Wirken an der Technischen Hochschule Danzig
Authors: Piosik Romuald
Published: July 2003

DAS JAHR 2003 ist in Deutschland das Jahr der Chemie. Es ist auch ein Jahr, in dem wir drei der berühmtesten Chemiker der Welt gedenken: Justus Liebig, Wilhelm Ostwald und Adolf Butenandt. Letzterem verdanken wir die Isolierung und Aufklärung der Sexualhormone und einer Vielzahl weiterer Naturstoffe. Einen wesentlichen Teil seiner Forschungsergebnisse hat er an der Technischen Hochschule zu Danzig gewonnen.
Theory of magnetic islands in tokamaks with accenting neoclassicaltearing modes
Authors: Mikhailovskii A.B.
Published: July 2003

Key aspects of existing theory of magnetic islands in tokamaks are overviewed. The threshold models of neoclassical tearing modes (NTMs) are discussed. It is found that though the NTM theory is often used for interpreting MHD data observed in experimental devices and for designing next‐step machines, the existing NTM theory is imperfect and the use of it is questionable. The main reason for such conclusion is a tangle of problems related to polarization current effect. Analytical approaches in the magnetic island theory are presented.
What really happens with the electron gas in the famous Franck‐Hertz experiment?
Authors: Sigeneger F. , Winkler R. , Robson R. E.
Published: July 2003

The interpretation of the anode current characteristics obtained in the famous Franck‐Hertz experiment of 1914 led to the verification of Bohr's predictions of quantised atomic states. This fundamental experiment has been often repeated, and nowadays is generally part of the curriculum in modern physics education. However, the interpretation of the experiment is typically based upon significant simplifying assumptions, some quite unrealistic. This is the case especially in relation to the kinetics of the electron gas, which is in reality quite complex, due mainly to non‐uniformities in the electric field, caused by a combination of accelerating and retarding components. This non‐uniformity leads to a potential energy valley in which the electrons are trapped. The present state of understanding of such effects, and their influence upon the anode characteristics, is quite unsatisfactory. In this article a rigorous study of a cylindrical Franck‐Hertz experiment is presented, using mercury vapour, the aim being to reveal and explain what really happens with the electrons under realistic experimental conditions. In particular, the anode current characteristics are investigated over a range of mercury vapour pressures appropriate to the experiment to clearly elaborate the effects of elastic collisions (ignored in typical discussions) on the power budget, and the trapping of electrons in the potential energy valley.
Polar recombination as the main process explaining the M‐effect
Authors: Musa G. , Baltog A.
Published: July 2003

A full explanation of the M‐effect, namely the reduction of the neon emission spectra practically to only one line of wavelength λ1 = 585.3 nm, when the filling gas is a mixture Ne + Ar + H2 or Ne + Xe + H2 is presented. The M‐effect is explained by ion‐ion recombination according to the reaction Ne+ H– = Ne*(2p1)+H, which feeds selectively the level 2p1 of neon. All observed behavior of the M‐effect is explained by polar recombination. Extension of the M‐effect to other gas mixtures containing at least one electronegative component is also underlined.
Synthesis and Structures of Compounds Based on Chalcocyanide Tetranuclear Rhenium Clusters: Bonding Cluster Complexes by diene‐Bridged CuII Units
Authors: Mironov Yuri V. , Efremova Olga A. , Naumov Dmitry Yu. , Sheldrick William S. , Fedorov Vladimir E.
Published: July 2003

Six new tetrahedral chalcocyanide cluster compounds, [{Cu2(dien)3}Re4S4(CN)12] (1), [{Cu(dien)(NH3)}2Re4Se4(CN)12]·2.5H2O (2), [{Cu2(dien)3}Re4Q4(CN)12]·nH2O (Q = Se (3), Te (4)] and [K(H2O)2]2[{Cu3(dien)4}{Re4Q4(CN)12}2]·8H2O where Q = Se (5), Te (6) (dien = diethylenetriamine), have been synthesized by treating aqueous solutions of the salt‐like cluster compounds K4Re4Q4(CN)12·nH2O with solutions of copper(II) chloride in aqueous ammonia containing diethylenetriamine. All six compounds have been characterized by single‐crystal X‐ray diffraction analysis. Compound 1 has a chain‐like polymeric structure; orthorhombic, space group Pmn21. Compound 2 has a molecular structure; triclinic, space group P
. Compounds 3 and 4 are isostructural and also exhibit molecular structures; monoclinic, space group P21/n. Compounds 5 and 6 are isostructural and display a cross‐bridged chain‐like polymeric structure; triclinic, space group P
. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Mono‐Dithiolene Molybdenum(IV) Complexes of cis‐1,2‐Dicyano‐1,2‐ethylenedithiolate (mnt2−): New Models for Molybdenum Enzymes
Authors: Sugimoto Hideki , Siren Kazushi , Tsukube Hiroshi , Tanaka Koji
Published: July 2003

New mono‐dithiolene molybdenum(IV) complexes of cis‐1,2‐dicyano‐1,2‐ethylenedithiolato [(mnt)2−] have been synthesized as models for molybdenum enzymes, with 4,4′‐di‐tert‐butyl‐2,2′‐bipyridine (Bu2bpy) and, N,N′‐tetraethylethylenediamine (Et4en) as ancillary ligands, and characterized by IR, UV/Vis, elemental analysis, ESI‐mass and electrochemical techniques. The temperature‐dependent 1H NMR spectra, recorded in CD3CN solution, indicated that [MoO(mnt)(Bu2bpy)] (1) has a rigid structure but [MoO(mnt)(Et4en)] (2) showed dynamic conformational inversion processes involving the chelating ethylenediamine unit. The complexes exhibited different reactivities toward molecular oxygen: 1 gave a single oxo‐bridged dimolybdenum dimer complex [Mo2O3(mnt)2(Bu2bpy)2] (3), while 2 did not react with O2 and kept its mononuclear structure. Both complexes have almost the same redox potential for MoIV/V, and so the steric bulkiness and conformational dynamics were thought to cause this marked contrast. The obtained dimolybdenum complex 3 was also structurally characterized and investigated, and found to be a new dimolybdenum complex with one dithiolene per molybdenum. The crystal structure of the starting complex 4 was also reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
New 1,3,4‐Oxadiazolecopper(II) Derivatives Obtained from Thiosemicarbazone Complexes
Authors: Gómez‐Saiz Patricia , García‐Tojal Javier , Maestro Miguel A. , Mahía José , Arnaiz Francisco J. , Lezama Luis , Rojo Teófilo
Published: July 2003

Pyridine‐2‐carbaldehyde thiosemicarbazone and pyridine‐2‐carbaldehyde 4N‐methyl thiosemicarbazone ligands (HLI and HLImm respectively) undergo an oxidative cyclization when treated with bromate or iodate, leading to 2‐amino‐5‐pyridin‐2‐yl‐1,3,4‐oxadiazole and 2‐methylamino‐5‐pyridin‐2‐yl‐1,3,4‐oxadiazole (HLII and HLIImm). This reaction occurs either with free ligands or when coordinated to copper(II). Some of the starting ([{Cu(LImm)(NO3)}2] (3), intermediate Cu(LI)(IO3)·(H2O) (1), [{Cu(LI)I}2] (2), [{Cu(LImm)Br}2] (4), and final compounds [{Cu(HLII)(H2O)3}2](SO4)2 (5), [{Cu(HLIImm)(H2O)2(SO4)}2]·2H2O (6), (HLII) (7), [HLIImm]·3H2O (8) have been isolated and characterized by elemental analyses, IR, UV‐visible, NMR, and EPR spectroscopy. The structures of 2, 3, 4, 5, 6, and 8, solved by X‐ray diffraction methods, contain dinuclear entities with either square‐pyramidal (2, 3, 4) or octahedral (5, 6) copper(II) ions. Structural and spectroscopic results suggest that ligand‐to‐metal charge transfer occurs in these compounds. The EPR spectra at 120 K exhibit rhombic (1, 3, 4), isotropic (2), and axial (5, 6) signals. Magnetic measurements show antiferromagnetic couplings for 2, 4, 5, and 6. The susceptibility data were fitted by the Bleaney−Bowers equation for copper(II) dimers. The obtained J/k values are −20.20, −8.85, −2.75, and −2.78 K for 2, 4, 5, and 6, respectively. However, ferromagnetic intradimeric interactions are present in 3 (J/k = +9.90 K) together with antiferromagnetic interdimer coupling (z′J′/k = −1.70 K). Magneto‐structural studies show the influence of the non‐thiosemicarbazone coligand in the magnetic behaviour of these complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses, Reactivity Studies and the Catalytic Properties of a Series of Tetraosmium−Gold Mixed‐Metal Clusters
Authors: Li Yat , Wong Wing‐Tak
Published: July 2003

Treatment of the mixture of [Os4(μ‐H)4(CO)12] and [AuPPh3Cl] with excess triethylamine afforded three novel tetraosmium−gold mixed‐metal clusters, [Os4Au2(μ‐H)2(CO)11(PPh3)3] (4), [Os4Au3(μ‐H)3(CO)11(PPh3)3] (5), and [Os4Au4(μ‐H)2(CO)11(PPh3)4] (6) in moderate yields. Cluster [Os4Au(μ‐H)3(CO)11(NMe3)(PPh3)] (2) was also obtained in a similar reaction in the presence of trimethylamineN‐oxide. They were fully characterized by different spectroscopic techniques, and the solid‐state structures were established by X‐ray analysis. These dimetallic clusters exhibit an osmium/gold ratio ranging from 1 to 4. Their electronic absorption properties, electrochemistry, and catalytic properties, as a result of the oxidative carbonylation of aniline, were investigated in terms of the Os/Au ratio. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Coordination of Actinide Ions in Wells−Dawson Heteropolyoxoanion Complexes
Authors: Chiang Ming‐Hsi , Williams Clayton W. , Soderholm L. , Antonio Mark R.
Published: July 2003

Although many low‐valent (III, IV) actinide (An) ions are known to form coordination complexes with the α‐2 isomer of the lacunary Wells−Dawson polyoxoanion, [P2W17O61]10−, there is little structural information about the An−O interactions, particularly in solution. We have probed the An−O coordination environment for the series of clusters [An(α‐2‐P2W17O61)2]n− with An4+ (Th4+, U4+, Np4+, Pu4+) and An3+ (Np3+, Pu3+, Am3+) in both solution and solid phases using X‐ray absorption fine structure (XAFS). Comparisons are made with the lanthanide (Ln) coordination environments in the series of 4f‐ion clusters, [Lnn+(α‐2‐P2W17O61)2]n−20, and with the related monovacant Lindqvist anions, [Lnn+(W5O18)2]n−12, for n = 3, 4. The average An−O8 and Ln−O8 distances correlate with their cationic VIII‐coordinate ionic radii, indicating that the An and Ln ions have indistinguishable coordination behavior. Metrical details are consistent with simple charge and size considerations for both trivalent and tetravalent An ions as well as Ln ions coordinated with α‐2‐[P2W17O61]10− and [W5O18]6−. This result is contrasted to trends established for these f‐ions coordinated to the Preyssler anion [Lnn+P5W30O110]n−15. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Three Novel Polymeric Frameworks Assembled from CdII, CoII, and MnII with the Mixed Organic Ligands 3,4‐Pyridinedicarboxylate, 1,3‐Bis(4‐pyridyl)propane, or 1,2‐Bis(4‐pyridyl)ethane
Authors: Fu Zhi‐Yong , Hu Sheng‐Min , Dai Jing‐Cao , Zhang Jian‐Jun , Wu Xin‐Tao
Published: July 2003

Hydrothermal reactions of CdII, CoII, and MnII with the mixed ligands 3,4‐pyridinedicarboxylate (pydc), 1,3‐bis(4‐pyridyl)propane (bpp), or 1,2‐bis(4‐pyridyl)ethane (bpe) gave crystals of {[Cd(pydc)(bpp)]·0.5H2O}n (1), {[Co(pydc)(H2O)(bpe)0.5]·0.5H2O}n (2), and {[Mn(pydc)(H2O)(bpe)0.5]· 0.5H2O}n (3), respectively. Single‐crystal X‐ray analyses reveal that these are all three‐dimensional non‐interpenetrating coordination polymers. Their structures alter markedly with the conformation and the function of the ligands. In 1, the 3,4‐pyridinedicarboxylate acted as a three‐connector, a coordination topology of the type (3,5) [containing 3 and 5 connected centers] being generated through self‐assembly, while in 2 and 3, with the help of the four‐connector 3,4‐pyridinedicarboxylate and the terminal ligand water molecule, another three‐dimensional framework with a coordination topology of the type (4, 5) was obtained. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Molecular Structures of Nickel(II) and Cobalt(III) Complexes with 2‐(Arylimino)‐3‐(hydroxyimino)butane
Authors: Zangrando Ennio , Trani Manuela , Stabon Elisa , Carfagna Carla , Milani Barbara , Mestroni Giovanni
Published: July 2003

We report new series of NiII and CoIII complexes with nitrogen‐donor chelating ligands of the (E,E)‐2‐(arylimino)‐3‐(hydroxyimino)butane type (Ar−N∩N−OH). These ligands are characterized by a hydrophilic (OH group) and a hydrophobic region (aryl group). NiII derivatives were obtained either as trimers of formula [Ni3(Ar−N∩N−OH)3Br4(OH)][Br], with the hydrophobic groups oriented on the same side, or as bis(chelated) derivatives with cis geometry, depending on the steric hindrance of the aryl groups. CoIII complexes were obtained only as bis(chelated) derivatives, with the two ligands coplanar. The “iso‐oriented” arrangement of ligands in bis(chelated) CoIII complexes is favored by weak interactions between the two ligands, namely O−H···O hydrogen bond and stacking interactions between the aryl groups. CoIII complexes might find application as catalysts for living or controlled radical polymerization of polar olefins, and preliminary results are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
NMR Investigation and Dynamic Behaviour of [2,2′‐Bipyridylbis(pyridine)platinum(II)]2+ and Related Cationic Complexes − Crystal Structure of [Pt(bipy)(py)2](PF6)2
Authors: Rotondo Enrico , Bruschetta Giuseppe , Bruno Giuseppe , Rotondo Archimede , Di Pietro Maria Letizia , Cusumano Matteo
Published: July 2003

Detailed 1H and 13C{1H} NMR analysis has been carried out on complexes with the general formulae [Pt(bipy)(n‐Rpy)2](PF6)2 and [Pt(4‐Phbipy)(n‐Rpy)2](PF6)2 [bipy = 2,2′‐bipyridyl; 4‐Phbipy = 4,4′‐diphenyl‐2,2′‐dipyridyl; n‐Rpy = pyridine or substituted pyridines]. The resonance assignments and X‐ray structures of these complexes are important steps on our route to: (i) interpretation of the intercalative geometry on the basis of the magnetic changes produced on interaction with DNA, (ii) rational design of new intercalators. The X‐ray structure of the parent complex [Pt(bipy)(py)2](PF6)2 (py = pyridine) shows pyridine rings quasiperpendicular to the coordination plane. In solution, because of the hindered rotation about Pt−N bonds of ortho‐ and meta‐monosubstituted pyridines, this arrangement leads to “head‐to‐head” s‐cis Cs and “head‐to‐tail” s‐trans C2 rotamers in equilibrium. NMR line shape and 13C relaxation time constant measurements were carried out in order to evaluate activation energies and anisotropic rotational motion of n‐Rpy. In some of these complexes a second dynamic process could be frozen on the 13C NMR timescale below 265 K. This lower activation energy process can reasonably be attributed to minimal bipyridyl torsion angle flipping driving a concerted molecular motion about the core of the four N‐donors. Indeed, the X‐ray structure of 1 proves distortion with a slight alternate up and down shift of the four nitrogen atoms about the coordination plane. Significantly, the fast rotation of unhindered pyridine rings does not allow NMR detection of this molecular distortion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Bis(2‐aminobutanol)dichloroplatinum(II) Complexes and Their Singly and Doubly Ring‐Closed Butanolato Species − Novel Prodrugs for Platinum‐Based Antitumour Chemotherapy?
Authors: Galanski Mathea Sophia , Baumgartner Christian , Arion Vladimir , Keppler Bernhard K.
Published: July 2003

Cytotoxic hydroxyethyl‐substituted (amine)platinum(II) and ‐(IV) complexes have recently attracted attention because of the ability of their hydroxyethyl groups to coordinate through the oxygen atom to the platinum centre during oxidation with hydrogen peroxide or through intramolecular ligand exchange reactions in dichloroplatinum(II) complexes. The last point in particular is of great interest, because the intramolecular attack of the hydroxy group dramatically influences the mode of action of platinum(II) compounds. On the other hand, there is also the chance to use such reactions specifically for the synthesis of novel anticancer platinum‐based drugs for chemotherapy. We have therefore focused our chemistry program on the synthesis of dichloroplatinum(II) complexes that are in a position to form singly and, especially, doubly ring‐closed alcoholato species and on investigation of their structures by X‐ray crystallography. It was possible to determine the crystal structures of [Pt{(R)‐(−)‐HL}2Cl2], [Pt{(S)‐(+)‐HL}2Cl2], [Pt{(R)‐(−)‐HL}{(S)‐(+)‐HL}Cl2], [Pt{(S)‐(+)‐HL}{(S)‐(+)‐L}Cl], [Pt{(R)‐(−)‐L}2] and [Pt{(S)‐(+)‐L}2] (HL = 2‐aminobutanol‐κN, L = 2‐aminobutanolato‐κ2N,O). The results obtained may represent the first step towards novel prodrugs for platinum‐based antitumour chemotherapy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Rhodium and Ruthenium Complexes of 1,1′‐Bis(phosphetano)ferrocenes: Structural Characterisation and Catalytic Behaviour
Authors: Marinetti Angela , Labrue Francis , Pons Bénédicte , Jus Sébastien , Ricard Louis , Genêt Jean‐Pierre
Published: July 2003

The first structural characterisation of ruthenium and rhodium complexes of the 1,1′‐bis(phosphetano)ferrocenes 1 (FerroTANEs) − namely [{(S,S)‐iPr‐1}RuCl2Py2] and [{(S,S)‐iPr‐1}Rh(COD)OTf] − is reported. X‐ray data show that the ruthenium complex and the rhodium chelate complex both adopt δ conformations, as a result of the (S,S) configuration of the phosphetane moiety. The ruthenium complexes promote the catalytic hydrogenation of β‐keto esters with moderate to high enantioselectivities. The behaviour of the rhodium complexes of 1 is compared with that of other phosphetane‐based catalysts in the hydrogenation of methyl N‐acetamidocinnamate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Reactions of Dihydrogen(norbornadiene) Complexes
Authors: Jia Guochen , Lin Zhenyang , Lau Chak Po
Published: July 2003

Dihydrogen(olefin) complexes have been proposed as active species in catalytic hydrogenation reactions. We have studied the hydrogen‐transfer reactions of dihydrogen(olefin) complexes, especially those containing the norbornadiene (NBD) ligand, in order to address the following questions: (i) how the alignment of a H2 ligand relative to an olefin ligand may affect their reactivity; (ii) in general, what is the detailed pathway for intramolecular hydrogen transfer from an H2 ligand to an olefin ligand; and (iii) how will the hydrogen transfer reactions proceed in the presence of both an H2 and a hydride ligand. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Two‐ and Three‐Dimensional Frameworks Constructed From Bicapped Keggin Clusters
Authors: Duan Li‐Mei , Pan Cheng‐Ling , Xu Ji‐Qing , Cui Xiao‐Bing , Xie Feng‐Tong , Wang Tie‐Gang
Published: July 2003

The novel two‐ and three‐dimensional solid materials [Cu(en)2(H2O)]{PMoVI8VIV6O42[Cu(en)2][Cu0.5(en)]3}·5.5H2O and H3{VVMoVI8VIV6O42[Cu(en)2]4}[MoO4]2·14H2O (en = ethylenediamine) have been hydrothermally assembled and structurally characterized. Both networks are based on mixed Mo/V bicapped Keggin clusters interconnected through the transition metal complex moieties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Diorganotin(IV) Complexes of a Cyclic Thiosemicarbazone Ligand: Crystal Structures of [SnPh2(C15H10N3S)Cl] and [SnMe2(C15H10N3S)2]
Authors: López‐Torres Elena , Mendiola M. Antonia , Pastor César J. , Procopio Jesús R.
Published: July 2003

Treatment of 5‐methoxy‐5,6‐diphenyl‐4,5‐dihydro‐2H‐[1,2,4]triazine‐3‐thione (LH2OCH3) with compounds SnR2X2 (R = Me and Ph; X = Cl and NO3) afforded, for the first time, metal derivatives of a cyclic thiosemicarbazone. Treatment of LH2OCH3 with the appropriate diorganotin(IV) chloride in dichloromethane provided 1:1 complexes, but 1:2 derivatives were isolated when the nitrate salts in distilled water were used. The complexes were studied by mass spectrometry, IR and multinuclear (1H, 13C and 119Sn) NMR in solution, and also by 119Sn CP/MAS NMR spectroscopy and by X‐ray diffraction in the solid state. In all the complexes, the thiosemicarbazone had been modified by formation of a new C=N bond. In addition, the ligand LH had lost a hydrogen atom, acting as an anion. The crystal structures of [SnPh2(C15H10N3S)Cl] (1) and [SnMe2(C15H10N3S)2] (4) each consist of discrete molecules with the tin atom bonded to the sulfur and amine nitrogen atoms to give a four‐membered chelate ring with the [1,2,4]triazine modified. For phenyl derivative 1, the tin atom is in a trigonal‐bipyramidal environment with the phenyl rings in equatorial positions, and for complex 4 it is in an octahedral arrangement, with the methyl groups in axial positions. The 119Sn CP/MAS NMR spectra of the complexes are in accordance with these structures. The values obtained indicate a five‐coordinate geometry for [SnMe2(C15H10N3S)Cl] (2) and suggest a coordination number of six for complex 3. The 119Sn spectra of complexes in solution depend on the coordinating capacity of the solvents. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Reactivity of Alkylzirconium Complexes Incorporating Asymmetrically Substituted ansa Ligands − X‐ray Crystal Structure of [Zr{Me2Si(η5‐C5Me4)(η5‐C5H3Me)}(CH2Ph)Cl]
Authors: Antiñolo Antonio , Fernández‐Galán Rafael , Gallego Beatriz , Otero Antonio , Prashar Sanjiv , Rodríguez Ana M.
Published: July 2003

The monoalkyl complexes [Zr{Me2Si(η5‐C5Me4)(η5‐C5H3R)}(R′)Cl] [R = Me, R′ = CH2Ph (1); R = Me, R′ = CH2SiMe3 (2); R = iPr, R′ = CH2Ph (3); R = iPr, R′ = CH2SiMe3 (4); R = SiMe3, R′ = CH2Ph (5); R = SiMe3, R′ = CH2SiMe3 (6)] have been synthesized by the reaction of the corresponding ansa‐metallocene dichloride complex and 1 equiv of the alkyl Grignard reagent. Dialkyl complexes with large alkyl groups only formed for the zirconocene complex containing the ansa ligand Me2Si(η5‐C5Me4)(η5‐C5H4) and with the benzyl substituent giving [Zr{Me2Si(η5‐C5Me4)(η5‐C5H4)}(CH2Ph)2] (7). When the alkyl substituent is CH2SiMe3 only the monoalkyl derivative, [Zr{Me2Si(η5‐C5Me4)(η5‐C5H4)}(CH2SiMe3)Cl] (8), was formed. The insertion reaction of the isocyanide reagent CNC6H3Me2‐2,6 into the zirconium−carbon σ‐bond of complexes 1−8 gave the corresponding η2‐iminoacyl compound [Zr{Me2Si(η5‐C5Me4)(η5‐C5H3R)}{η2‐R′C=NC6H3Me2‐2,6}Cl] [R = Me, R′ = CH2Ph (9); R = Me, R′ = CH2SiMe3 (10); R = iPr, R′ = CH2Ph (11); R = iPr, R′ = CH2SiMe3 (12); R = SiMe3, R′ = CH2Ph (13); R = SiMe3, R′ = CH2SiMe3 (14); R = H, R′ = CH2SiMe3 (16)] and [Zr{Me2Si(η5‐C5Me4)(η5‐C5H4)}{η2‐PhCH2C=NC6H3Me2‐2,6}(CH2Ph)] (15). The molecular structure of 1 has been determined by single‐crystal X‐ray diffraction studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Novel One‐Dimensional Chain Complex Composed of Oxo‐Centered Trinuclear Manganese Clusters
Authors: Kim Jinkwon , Lim Jin Mook , Do Youngkyu
Published: July 2003

A new linear chain complex of oxo‐centered trinuclear manganese clusters, [{MnIII2MnIIO(O2CCHCl2)6(H2O)}{Mn(O2CCHCl2)2(H2O)4}]n (1), has been synthesized by treatment of a mixture of Mn(OAc)2·4H2O and dichloroacetic acid in dichloromethane with KMnO4. In this complex chains are formed by hydrogen bonding between carboxylate oxygens and coordinated water molecules, forming a two‐dimensional structure. Antiferromagnetic coupling was observed by variable‐temperature magnetic measurements. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Novel Three‐Dimensional Metal‐Organic Framework Constructed from Two‐Dimensional Interpenetrating Layers Based on Trinuclear Cobalt Clusters: [Co3(btec)(C2O4)(H2O)2]n
Authors: Li Yang‐Guang , Hao Na , Wang En‐Bo , Lu Ying , Hu Chang‐Wen , Xu Lin
Published: July 2003

A novel coordination polymer [Co3(btec)(C2O4)(H2O)2]n (1; btec = 1,2,4,5‐benzenetetracarboxylate) has been hydrothermally synthesized and characterized by IR, XPS, XRPD, TG analysis and single‐crystal X‐ray diffraction. The structural analysis reveals that 1 exhibits a new three‐dimensional metal‐organic framework constructed from two‐dimensional parallel interpenetrating networks based on trinuclear cobalt cluster building blocks. Such interpenetrating composite networks in 1 represent the first example in the {M‐btec} (M = transition metal) system. Variable‐temperature magnetic susceptibility measurements indicate an antiferromagnetic behavior in 1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Blue to Red Fluorescent Emission Tuning of a Cadmium Coordination Polymer by Conjugated Ligands
Authors: Zhang Jing , Xie Yong‐Rong , Ye Qiong , Xiong Ren‐Gen , Xue Ziling , You Xiao‐Zeng
Published: July 2003

The hydrothermal hydrolysis reactions of Cd(ClO4)2·(6H2O) with 4‐[2‐(2‐pyridyl)ethenyl]benzonitrile (2‐PEBN) and 2‐[2‐(4‐cyanophenyl)ethenyl]‐8‐quinolinol (2‐CEQH) afforded two coordination polymers aquabis{4‐[2‐(2‐pyridyl)ethenyl]benzoate}cadmium(II) (1) and 2‐[2‐(4‐carboxylatophenyl)ethenyl]‐8‐quinolinolate(pyridine)cadmium(II) (2), respectively. Complexes 1 and 2 display strong blue and red fluorescent emission, respectively. Both 1 and 2 have a 2‐D grid framework containing a dimer as the corner unit. Crystal data for 1: monoclinic, P21/c, a = 15.2411(2), b = 19.8651(2), c = 15.6929(1) Å, α = β = 90, γ = 96.961(1)°; for 2: monoclinic, P21/c, a = 11.9219(1), b = 8.9515(1), c = 18.8204(1)Å, α = γ = 90.00, β = 104.372(1)°. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Von Läusen und Ameisen
Authors: Hoffmann Klaus H. , Fischer Melanie , Völkl Wolfgang , Lorenz Matthias W.
Published: July 2003

Aus dem Saft ihrer Wirtspflanze produziert die Blattlaus Honigtau. Diese zuckerhaltige Substanz wird von Ameisen besonders geschätzt
Im Stress werden Pilze und Pflanzen Partner
Authors: Bothe Hermann , Hildebrandt Ulrich
Published: July 2003

80 Prozent aller Pflanzen leben in einer Symbiose mit Mykorrhiza‐Pilzen. Die molekularen Grundlagen dieser Lebensgemeinschaft stehen im Mittelpunkt eines DFG‐Schwerpunktprogramms
Kommentar: Perspektiven für eine lebendige Community
Authors: Peters Ursula
Published: July 2003

Die Geisteswissenschaften fordern flexible Förderinstrumente — Besonderen Bedürfnissen sollte Rechnung getragen werden
Im Blickpunkt: Ein Hauch von Nichts
Authors: Greiner Andreas , Steinhart Martin , Wendorff Joachim H. , Wehrspohn Ralf
Published: July 2003

In der Nanowelt spielen röhrenförmige Objekte eine besondere Rolle. Um Nanoröhrchen herzustellen, werden neue Präparationsverfahren entwickelt, die Grundlagen für eine Vielzahl technischer Anwendungen legen
Ultrafast Electron Diffraction (UED)
Authors: Srinivasan Ramesh , Lobastov Vladimir A. , Ruan Chong‐Yu , Zewail Ahmed H.
Published: July 2003

With properly timed sequences of ultrafast electron pulses, it is now possible to image complex molecular structures in the four dimensions of space and time with resolutions of 0.01 Å and 1 ps, respectively. The new limits of ultrafast electron diffraction (UED) provide the means for the determination of transient molecular structures, including reactive intermediates and non‐equilibrium structures of complex energy landscapes. By freezing structures on the ultrafast timescale, we are able to develop concepts that correlate structure with dynamics. Examples include structure‐driven radiationless processes, dynamics‐driven reaction stereochemistry, pseudorotary transition‐state structures, and non‐equilibrium structures exhibiting negative temperature, bifurcation, or selective energy localization in bonds. These successes in the studies of complex molecular systems, even without heavy atoms, and the recent development of a new machine devoted to structures in the condensed phase, establish UED as a powerful method for mapping out temporally changing molecular structures in chemistry, and potentially, in biology. This review highlights the advances made at Caltech, with emphasis on the principles of UED, its evolution through four generations of instrumentation (UED‐1 to UED‐4) and its diverse applications.
Enantioselective Preparation of 2‐Aminomethyl Carboxylic Acid Derivatives: Solving the β2‐Amino Acid Problem with the Chiral Auxiliary 4‐Isopropyl‐5,5‐diphenyloxazolidin‐2‐one (DIOZ). Preliminary Communication
Authors: Seebach Dieter , Schaeffer Laurent , Gessier François , Bindschädler Pascal , Jäger Corinna , Josien Delphine , Kopp Sascha , Lelais Gérald , Mahajan Yogesh R. , Micuch Peter , Sebesta Radovan , Schweizer Bernd W.
Published: July 2003

Multigram amounts of suitably protected β2‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2–8 thus obtained are converted to protected β2‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield.
Synthesis and CD Spectra of Fluoro‐ and Hydroxy‐Substituted β‐Peptides
Authors: Gessier François , Noti Christian , Rueping Magnus , Seebach Dieter
Published: July 2003

β‐Amino acids 1–3 with OH and F substituents in the α‐position have been prepared (Scheme) from the natural (S)‐α‐amino acids alanine, valine, and leucine, and incorporated into β‐hexa‐ and β‐heptapeptides 4–12. The peptide syntheses were performed according to a conventional solution strategy (Boc/Bn protection) with fragment coupling. The new β‐peptides with (series a) and without (series b) terminal protection were isolated in HPLC‐pure form and characterized by NMR spectroscopy and MALDI mass spectrometry. The chemical properties as well as the patterns of the CD spectra (Figs. 3–5) depend upon constitution (OH, F, F2 substitution) and configuration (l or u) of the amino acid residues, upon the total number of OH and F substituents in the peptide chain, and upon the solvent used (H2O, MeOH, CF3CH2OH, (CF3)2CHOH). No reliable clues regarding the structures can be obtained from these CD spectra. Only a full NMR analysis will be able to answer the questions: a) with which known secondary structures (Figs. 1 and 2) of β‐peptides are the OH and F derivatives compatible? b) Are new secondary structures enforced by the polar and/or H‐bonding backbone substituents? Furthermore, the β‐peptides described here will enable us to study changes in chemical, enzymatic, and metabolic stability, and in physiological properties caused by the heteroatoms.
Synthesis and Conformational Analysis of Macrocyclic Dilactones Mimicking the Pharmacophore of Aplysiatoxin
Authors: Knust Henner , Hoffmann Reinhard W.
Published: July 2003

A small number of macrocyclic dilactones of type 3, i.e., 9, 10, 11, and epi‐11, comprising a 3,4‐dihydroxypentanoic acid unit, the pharmacophore of aplysiatoxin, and a conformationally preorganized ω‐hydroxynonanoic acid unit were synthesized. Conformational analysis – based on 2J and 3J NMR coupling constants – of the dihydroxypentanoyl part of these macro‐dilactones indicates the extent to which a conformation induction across the macro‐dilactone ring occurs from the stereogenic centres implemented in the ω‐hydroxynonanoic acid part.
Synthesis and α‐Mannosidase Inhibitory Evaluation of (2R,3R,4S)‐ and (2S,3R,4S)‐2‐(Aminomethyl)pyrrolidine‐3,4‐diol Derivatives
Authors: Popowycz Florence , Gerber‐Lemaire Sandrine , Rodriguez‐García Eliazar , Schütz Catherine , Vogel Pierre
Published: July 2003

The synthesis of 46 derivatives of (2R,3R,4S)‐2‐(aminomethyl)pyrrolidine‐3,4‐diol is reported (Scheme 1 and Fig. 3), and their inhibitory activities toward α‐mannosidases from jack bean (B) and almonds (A) are evaluated (Table). The most‐potent inhibitors are (2R,3R,4S)‐2‐{[([1,1′‐biphenyl]‐4‐ylmethyl)amino]methyl}pyrrolidine‐3,4‐diol (3fs; IC50(B)=5 μM, Ki=2.5 μM) and (2R,3R,4S)‐2‐{[(1R)‐2,3‐dihydro‐1H‐inden‐1‐ylamino]methyl}pyrrolidine‐3,4‐diol (3fu; IC50(B)=17 μM, Ki=2.3 μM). (2S,3R,4S)‐2‐(Aminomethyl)pyrrolidine‐3,4‐diol (6, RH) and the three 2‐(N‐alkylamino)methyl derivatives 6fh, 6fs, and 6f are prepared (Scheme 2) and found to inhibit also α‐mannosidases from jack bean and almonds (Table). The best inhibitor of these series is (2S,3R,4S)‐2‐{[(2‐thienylmethyl)amino]methyl}pyrrolidine‐3,4‐diol (6o; IC50(B)=105 μM, Ki=40 μM). As expected (see Fig. 4), diamines 3 with the configuration of α‐D‐mannosides are better inhibitors of α‐mannosidases than their stereoisomers 6 with the configuration of β‐D‐mannosides. The results show that an aromatic ring (benzyl, [1,1′‐biphenyl]‐4‐yl, 2‐thienyl) is essential for good inhibitory activity. If the C‐chain that separates the aromatic system from the 2‐(aminomethyl) substituent is longer than a methano group, the inhibitory activity decreases significantly (see Fig. 7). This study shows also that α‐mannosidases from jack bean and from almonds do not recognize substrate mimics that are bulky around the O‐glycosidic bond of the corresponding α‐D‐mannopyranosides. These observations should be very useful in the design of better α‐mannosidase inhibitors.
Pre‐Irradiation Grafting of Styrene/Divinylbenzene onto Poly(tetrafluoroethylene‐co‐hexafluoropropylene) from Non‐Solvents
Authors: Rager Timo
Published: July 2003

Pre‐irradiation grafting of styrene/divinylbenzene (DVB) onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films was studied with respect to the influence of solvent. Particularly favorable grafting conditions with long radical lifetimes and reasonably high polymerization rates were achieved with solvents that are precipitants for the newly formed polystyrene, e.g., low‐molecular‐mass alcohols like iPrOH, AcOH, their mixtures with H2O, and H2O/surfactant systems. Using one of these solvents significantly extended the range of accessible graft levels, and a specific degree of grafting was obtained at a much lower monomer concentration and irradiation dose than with grafting in a good solvent such as toluene. As practical consequences, the monomer was used more efficiently, and the radiation damage of the perfluorinated base material was reduced with the result of improved mechanical properties of the grafted films.
Highly Soluble and Green Indigo Dyes: 4,4′,7,7′‐Tetraalkoxy‐5,5′‐diaminoindigotins
Authors: Voss Gundula , Gradzielski Michael , Heinze Jürgen , Reinke Helmut , Unverzagt Carlo
Published: July 2003

Two new types of 4,4′,7,7′‐tetraalkoxyindigotins, 1a–f and 2a–f along with the new N‐substituted indigotins 4e–f, were synthesized from dinitrobenzaldehydes 5a–f, which were prepared from 2‐hydroxy‐5‐methoxybenzaldehyde (7) via dialkoxybenzaldehydes 6a–f (Scheme). The new dialkoxyindigotin 3g was obtained from dialkoxybenzaldehyde 6g via nitrobenzaldehyde 8g. The 1,4‐dialkoxy‐2,3‐dinitrobenzenes 9 were isolated as by‐products. The 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 are soluble in organic solvents, and their solutions are green, which is highly uncommon for indigotins and is primarily caused by electronic effects of substituents, steric effects playing a minor role. The indigotins 1 produce a strong red shift of the longest‐wavelength absorption and negative solvatochromism indicating the predominance of polar resonance structures in the ground state. Tautomeric structures were excluded. These indigotins are valuable compounds for technical applications, for synthetic purposes, and for analytical studies. SANS (Small‐angle neutron scattering) experiments showed that certain 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 form rod‐like aggregates in solution. The similarly substituted 4,4′,7,7′‐tetraalkoxy‐5,5′‐dinitroindigotins 2 are far less soluble. They produce red monoanions (preferably dimers) and bluish‐purple dianions in organic solvents.
The Effectivity of 1H‐Triazoles and ‐Tetrazoles as Activators in Acid‐Catalyzed Phosphoramidite Alcoholysis
Authors: Nurminen Erkki. J. , Mattinen Jorma K. , Lönnberg Harri
Published: July 2003

The efficiency of 5‐nitro‐1,2,4‐1H‐triazole (3), 5‐(methylthio)‐1H‐tetrazole (4), and 5‐(4‐nitrophenyl)‐1H‐tetrazole (5) as activators in phosphoramidite alcoholysis has been studied relative to 1H‐tetrazole (6). Reactions of these azoles with diisopropyl (diisopropylamido)phosphite (1a) were followed in THF, and the rates were found to increase with increasing acidity of the azoles. The Brønsted α value of 0.7 determined for this dependence is in agreement with data published earlier.
Total Synthesis of the Marine Sesquiterpene Quinones Hyatellaquinone and Spongiaquinone
Authors: Bernet Andreas , Schröder Jörg , Seifert Karlheinz
Published: July 2003

The synthesis of the marine sesquiterpene quinone (+)‐hyatellaquinone (1) was achieved starting from the sesquiterpene aldehyde (+)‐albicanal ((+)‐3) (Schemes 3 and 4). Coupling of (+)‐albicanal with 2,3,5,6‐tetramethoxyphenyllithium led to the aryl‐sesquiterpene system, which was modified to the target molecule. Furthermore, the first total synthesis of the marine compound spongiaquinone (2) was carried out starting from ((−)‐albicanal (−)‐3) in a reaction sequence encompassing a stereoselective CC bond hydrogenation and a one‐pot AcOH elimination/demethylation reaction (Schemes 7 and 10). The occurrence of 1,2‐ and 1,4‐benzoquinone forms of 1 and 2 depends on the pH of the solvent system.
New Glycosides from Salvia moorcroftiana (Lamiaceae)
Authors: Zahid Muhammad , Saeed Muhammad , Asim Muhammad , Ishrud Omar , Wu Shihua , Ahmad Viqar Uddin , Pan Yuanjiang
Published: July 2003

From the MeOH extract of Salvia moorcroftiana Wall. (Lamiaceae), four new compounds, the two flavonoid glycosides genkwanin 4′‐[O‐α‐L‐rhamnopyranosyl‐(1→2)‐β‐D‐galactopyranoside] (1) and genkwanin 4′‐[O‐α‐L‐arabinopyranosyl‐(1→3)‐α‐L‐rhamnopyranoside] (2), and the two benzene derivatives 4‐hydroxy‐2‐isopropyl‐5‐methylphenyl O‐α‐L‐rhamnopyranosyl‐(1→2)‐β‐D‐glucopyranoside (3) and nonyl 4‐hydroxybenzoate (4), were isolated in addition to two known compounds. The structures of all new compounds were determined by 1D and 2D homonuclear and heteronuclear NMR spectroscopy and by comparison with published data.
Synthesis of the Spermidine Alkaloids (−)‐(2R,3R)‐ and (−)‐(2R,3S)‐3‐Hydroxycelacinnine: Macrocyclization with Oxirane‐Ring Opening and Inversion via Cyclic Sulfamidates
Authors: Khanjin Nikolai A. , Hesse Manfred
Published: July 2003

The two epimers (−)‐1a and (−)‐1b of the macrocyclic lactam alkaloid 3‐hydroxycelacinnine with the (2R,3R) and (2R,3S) absolute configurations, respectively, were synthesized by an alternative route involving macrocyclization with the regio‐ and stereoselective oxirane‐ring opening by the terminal amino group (Schemes 2 and 6). Properly N‐protected chiral trans‐oxirane precursors provided (2R,3R)‐macrocycles after a one‐pot deprotection‐macrocyclization step under moderate dilution (0.005–0.01M). The best yields (65–85%) were achieved with trifluoroacetyl protection. Macrocyclization of the corresponding cis‐oxiranes was unsuccessful for steric reasons. Inversion at OHC(3) via nucleophilic displacement of the cyclic sulfamidate derivative with NaNO2 led to (2R,3S)‐macrocycles. The synthesized (−)‐(2R,3S)‐3‐hydroxycelacinnine ((−)‐1b) was identical to the natural alkaloid.
New Tetracyclic Colchicinoids from the Reaction of N‐Deacetylthiocolchicine and N‐Deacetylcolchicine with Nitrous Acid and tert‐Butyl Nitrite
Authors: Danieli Bruno , Lesma Giordano , Passarella Daniele , Prosperi Davide , Sacchetti Alessandro , Silvani Alessandra , Destro Riccardo , May Emanuela , Bombardelli Ezio
Published: July 2003

Reaction of N‐deacetylthiocolchicine (3) and N‐deacetylcolchicine (4) with nitrous acid (HONO) furnished the new tetracyclic colchicinoids 5 and 6, as well as the Demyanov‐rearrangement products 7 and 8. Starting from 3, the pyrazole‐containing tetracycle 9 was obtained. The novel compounds were characterized spectroscopically, and an X‐ray crystal‐structure analysis of 5 allowed us to establish the absolute configurations at the stereogenic centers.