bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antibiotics from Gliding Bacteria, LXXVI. Vioprolides: New Antifungal and Cytotoxic Peptolides from Cystobacter violaceus
Authors: Schummer Dietmar , Höfle Gerhard , Forche Edgar , Reichenbach Hans , Wray Victor , Domke Tobias 
Published: June 2010

AbstractThe antifungal and cytotoxic metabolites vioprolides A‐D (1–4) were obtained from the myxobacterium Cystobacter violaceus strain Cb vi35 by fermentation in the presence of the adsorber resin XAD‐1180. Peptolide structures 1–4 composed of eight amino acids and a glyceric acid were determined by spectroscopic methods and total hydrolysis. The absolute configurations of the building blocks were established by GC analysis on chiral stationary phases. Common building blocks of 1–4 are l‐Ala, l‐Cys, D‐Leu, l‐Thr, l‐MeVal, (E)‐dehydrobutyrine (E‐Dhb), and l‐glyceric acid (l‐Gla). Two variable positions are occupied by l‐Pro or l‐Homopro and l‐Pro or trans‐(2S,4R)‐4‐methylazetidinecarboxylic acid [(2S,4R)‐Maz]. Two defined isomers of 1 were detected in CDCl3 in a ratio of 3 : 2 (2D‐1H NOESY) and assigned to rotational isomers at the amide bond of ThrMeVal.
Chiral Lactols, XIV. Stereoselective Fusion of Five‐Membered Ring Lactols to the Bornane Ring System
Authors: Noe Christian R. , Knollmüller Max , Gärtner Peter , Mereiter Kurt , Steinbauer Gerhard 
Published: June 2010

AbstractCondensation of d‐camphor (b) with diethyl oxalate and subsequent ester hydrolysis yielded camphoroxalic acid 3. endo‐Fused lactone 9 was obtained by reduction of 3 with zinc followed by reduction with NaBH4 and ring closure with H2SO4. exo‐Fused lactone 16, the crystal structure of which was determined, was prepared by reduction of 3 with NaBH4 under basic conditions followed by catalytic hydrogenation and ring closure with HCl. Reduction of 9 and 16 with DI‐BALH and application of acidic work‐up conditions yielded the self‐condensed reduction products (lactol anhydrides) 10 and 17, which are useful reagents in racemate resolution and stereoselective synthesis.
Oligophenylene Rods: A Repetitive Approach
Authors: Liess Petra , Hensel Volker , Schlüter A.‐Dieter 
Published: June 2010

AbstractThe concept of repetitive synthesis was successfully applied to oligophenylenes. A series of monodisperse rigid‐rods with up to 16 phenylene rings and with defined functional groups at both termini was prepared using the Suzuki cross‐coupling reaction.
Synthesis of Sphingosine Relatives, XVIII!. Synthesis of Penazetidine A, an Alkaloid Inhibitor of Protein Kinase C Isolated from the Marine Sponge Penares sollasi
Authors: Yajima Arata , Takikawa Hirosato , Mori Kenji 
Published: June 2010

AbstractTwo stereoisomers of penazetidine A (1a), the azetidine alkaloid isolated from the Indo‐Pacific marine sponge Penares sollasi, were synthesized by starting from (S)‐serine and (R)‐or (S)‐citronellol. The natural penazetidine A must be either (2S,3R,4S,12′R)‐ or (2S,3R,4S,12′S)‐1a.
Pigments of Fungi, 65! Synthesis of Haematopodin – a Pigment from the Mushroom Mycena haematopus (Basidiomycetes)
Authors: Hopmann Cordula , Steglich Wolfgang 
Published: June 2010

AbstractHaematopodin (1), a pigment from fruit bodies of the mushroom Mycena haematopus, was synthesized from 6,7‐bis‐(benzyloxy)indole (5). Key steps in the synthesis were the addition of 3‐[(2,4‐dimethoxybenzyl)amino]‐1‐propanol (11) to the indolo‐6,7‐quinone 10 and cyclization of the resulting adduct 12 with trifluoroacetic acid.
anti‐Selective Aldol Reactions of Amino Acid Ester Enolates. Application to the Synthesis of α‐Alkylated β‐Hydroxy Amino Acids
Authors: Grandel Roland , Kazmaier Uli , Nuber Bernhard 
Published: June 2010

AbstractDeprotonation of N‐protected esters of the amino acids alanine 1, ethylglycin 6, valine 7, and phenylalanine 8 with LDA and subsequent addition of various metal salts result in the formation of a probably chelated metal enolate. Aldol reactions of these enolates with aldehydes afford the anti isomers of α‐alkylated α‐amino‐β‐hydroxy acids in a highly diastereoselective fashion. Best results are obtained with titanium enolates, bulky aliphatic aldehydes, and sterically demanding amino acids.
Dithio and Thiono Esters, 64. Attempted Synthesis of Bis(alkylthio)‐Orthoqinodimethanes from Dithiobenzoates
Authors: Hartke Klaus , Bien Notker , Massa Werner , Wocadlo Sigrid 
Published: June 2010

Abstracto‐Alkyl substituted dithiobenzoates 3 are S‐methylated with trimethyloxonium tetrafluoroborate to form the stable bis(alkylthio)arylmethylium tetrafluoroborates 4. Their deprotonation with LiHMDS takes place either at the o‐alkyl groups to form the postulated o‐quinodimethanes 5 as intermediates or at the SMe groups to give the thiocarbonyl ylides 7. Both intermediates dimerize to furnish either the dibenzo[a,e]cyclooctenes 6 or the 1,4‐dithianes 8/9. Their trapping with N‐phenylmaleimide (10) leads to the formation of the cycloadducts 11 or 12. The structure of 8e was confirmed by X‐ray analysis. p‐Substituted dithiobenzoates 13 show a similar reaction sequence. Their bis(methylthio)arylmethylium salts, however, are only deprotonated at one of the SMe groups to give the 1,4‐dithianes 15/16. Sterically crowded 1,4‐dithianes (e.g. 8d,e/9d,e) rearrange with traces of acid to the ring opened stilbenes 18 and 19.
(Z)‐ und (E)‐Enole von diarylsubstituierten β‐Ketocarbonsäurederivativen
Authors: Buß Monika , Mayer Axel , Müller Klaus , Meier Herbert 
Published: June 2010

(Z) and (E) Enols of Diaryl‐Substituted β‐Ketocarboxylic Acid DerivativesThermolysis of the 1,3‐diaryl‐2‐diazo‐1,3‐propanediones 4 in the presence of alcohols or amines yielded the compounds 7–11 which exist as chelated (Z) enols or as tautomeric ketones. Contrary to the steric interaction of two mesityl groups the steric interaction between two naphthyl or two anthryl groups or between naphthyl and mesityl is not sufficient to stabilize the corresponding (E) enols. The latter isomers were generated in irradiation processes of some (Z) enols. Detailed NMR studies were performed in order to characterize the enols and their molecular dynamics.
Synthesis of Medium‐Size Macrocycles by Cinnamate [2 + 2] Photoaddition
Authors: König Burkhard , Leue Stefanie , Horn Clemens , Caudan Arnaud , Desvergne Jean‐Pierre , Bouas‐Laurent Henri 
Published: June 2010

AbstractUnsaturated macrocycles were obtained by [2 + 2] photoaddition of acyclic biscinnamates. The orientation of the chromophores by ortho‐xylyl (2) or aryl‐1,2‐diynyl (6) spacers leads to the formation of photoproducts in solution as single stereoisomers in high yield. The analogous photocyclization of a cis‐enediyne biscinnamate 4 was less efficient, because of a rapid photochemical isomerization of the central double bond.
Synthetic Studies of Glycosyl Serines in the Carbohydrate‐Protein Region of Protoglycans
Authors: Tamura Jun‐Ichi , Neumann Klaus W. , Ogawa Tomoya 
Published: June 2010

AbstractA series of glycosyl serines 1–6 which are located in the carbohydrate‐protein linkage region of proteoglycans, including the chondrottin penta‐ and heptasaccharides GalNAcα(1–4)R (3), GalNAcß(1–4)R (4) and GalNAcß(1–4)GlcAß(1–3)GalNAc(1–4)R (6) as well as the heparin pentasaccharide GlcNAcα(1–4)R (5) [R = GlcAß(1–3)Galß(1–3)Galß(1–4)Xylß‐Ser] were systematically synthesized as follows. Trisaccharide acceptor 27 having a Gal(1–3)Galß(1–4)Xyl sequence was glycosylated with di‐ and tetrasaccharide donors 16α, 16ß, 22, and 26, which correspond to the non‐reducing end sequences of 3–6, regio‐ and stereoselectively to afford penta‐ and heptasaccharides 30, 34, 36, and 39, respectively. After the conversion into the respective penta‐ and heptaosylimidates 42c‐f as well as tri‐ and tetraosylimidates 42a and b, they were coupled with serine derivative 43 to give tri‐, tetra‐, penta‐, and heptaosyl serines 44a‐f. All the glycosyl serines were deprotected to 1–6.
Novel Dienes and Dienophiles, VII Preparation and Chemical Behavior of 2,3‐Diethynyl‐1,3‐butadiene
Authors: Hopf Henning , Theurig Marcus , Bubenitschek Peter , Jones Peter G. 
Published: June 2010

AbstractThe two 2,3‐diethynyl‐1,3‐butadiene derivatives 1b and 1c were prepared from 2,3‐dichloro‐1,3‐butadiene (26) and the Grignard reagents 19b and 19c by Kumada coupling. Desilylation of 1b provided the parent molecule 1a. The title compounds were used for the preparation of numerous new enediyne systems by [2 + 4] cycloaddition. The dienophiles employed include maleic anhydride (27a), diethyl fumarate (29), tetracyanoethylene (31), diethyl azodicarboxylate (33), and dimethyl acetylenedicarboxylate (35). With p‐quinones such as p‐benzoquinone (44) as dienophiles the expected mono‐and bisadducts are formed which were dehydrogenated to the bis‐ and tetrakis(trimethylsilylethynyl)naphtho‐ and ‐anthraquinones 47 and 48, respectively, by treatment with DDQ. Heating of 1b in THF at 65°C caused dimerization to the 1,5‐cyclooctadiene derivative 56, which was desilylated to 1,2,5,6‐tetraethynyl‐1,5‐cyclooctadiene (59) by treatment with potassium fluoride in DMF. 1b is approximately 15 times less reactive than 2,3‐dimethyl‐1,3‐butadiene (54) towards maleic anhydride (27a).
Zur Energiedelle von Diradikalen, VI. Das Energieprofil der NO2‐Addition an konjugierte Doppelbindungen: Eine Reaktion mit negativer Aktivierungsenergie
Authors: Roth Wolfgang R. , Bastigkeit Thorsten , Börner Sabine 
Published: June 2010

On the Energy Well of Diradicals, VIPart V: Ref. [1]

.
– The Energy Profile for the NO2‐Addition to Conjugated Double Bonds: A Reaction with Negative Activation Energy
From the NO and temperature dependence of the reaction rates of 1,3‐butadiene, styrene, and methylenebenzocyclobutene with NO2 in the presence of NO, the energy profiles for the formation of the primary adducts are derived, which explain the inverse temperature dependence for the disappearance of the substrate at low NO concentrations and allow to calculate the bond strength of the C–NO2 bond (57.9 ± 1.3 kcal · mol−1).
Zur Energiedelle von Diradikalen, VIII. Das Energieprofil der entarteten Methylencyclobutan‐Umlagerung
Authors: Roth Wolfgang R. , Paschmann Volker 
Published: June 2010

On the Energy Well of Diradicals, VIIIPart VII: Ref.

.
– Energy Profile of the Degenerate Methylenecyclobutane Rearrangement
From the temperature and oxygen dependence of the trapping rates of the diradicals 4 and 6, recombination enthalpies of 4.7 and 1.8 kcal · mol−1 are derived. These enthalpies agree well with estimates from our reaction force field (5.5 and 2.0 kcal · mol−1). The increasing stereoselectivity in the methylenecyclobutane rearrangement 1a → 1b with electronically less stabilizing substituents (R = Ph, CH3) is related to the decreasing recombination enthalpy of the intermediate diradical 2. This finding can be rationalized from the changing curve of the electronic energy during the recombination.
Diastereo‐ and Enantioselective Synthesis of Lignan Building Blocks by Tandem Michael Addition/Electrophilic Substitution of Lithiated α‐Amino Nitriles to Furan‐2(5H)‐one
Authors: Enders Dieter , Kirchhoff Jochen , Lausberg Vivien 
Published: June 2010

AbstractStarting from chiral α‐amino nitriles (S,S,R/S)‐3, we prepared β‐aroyl‐γ‐butyrolactones (S)‐5as well as 2,3‐disubstituted γ ‐butyrolactones (S,S)‐ or (R,S,R)‐6in high yields and with high enantiomeric excesses by conjugate addition to butenolide, followed by protonation, α‐alkylation or α‐aldol addition, respectively. The introduction of one up to three stereogenic centers opens a flexible and highly efficient diastereo‐ and enantioselective route to 2,3‐dibenzylated γ‐butyrolactones6, which proved to be important lignan building blocks.
Thermal Rearrangements, XXV. The Automerization of Benzene as A Radical‐Initiated Reaction
Authors: Zimmermann Gerhard , Nüchter Matthias , Hopf Henning , Ibrom Kerstin , Ernst Ludger 
Published: June 2010

AbstractThe thermal isomerization of [1,4‐D2]‐ (3a) and [1,2‐13C2]benzene (1a) has been studied in excess hydrogen at 750–850°C with contact time less than 1.2 s and very low partial pressure in a quartz flow system. In both cases, the main isomerization products are the corresponding meta isomers. The data suggest a radical intramolecular interchange of the benzene carbon atoms by 1,2‐C shifts. The multistep reaction cascade is initiated by H addition to the benzene ring followed by transannular homoallyl rearrangements involving the intermediate formation of bicyclo[3.1.0]hexenyl and cyclopentadienylmethyl radicals. This pathway constitutes a side reaction competing with the direct stabilization of the cyclohexadienyl radicals formed preferentially at high temperature.
Enzymes in Organic Synthesis, 26. Synthesis of Enantiomerically Enriched 2,3‐ and 3,4‐Dimethylpentan‐5‐olides by Lipase‐Catalyzed Regio‐ and Enantioselective Alcoholysis of cis‐ and trans‐2,3‐Dimethylpentanedioic Anhydrides
Authors: Ozegowski Rüdiger , Kunath Annamarie , Schick Hans 
Published: June 2010

AbstractThe enzyme‐catalyzed regio‐ and enantioselective alcoholysis of racemic cis‐ and trans‐2,3‐dimethylpentanedioc anhydride in the presence of Novozym 435 from Candida antarctica afforded two of the eight possible monoesters with an enantiomeric excess higher than 90%. Regioselective reductions of these monoesters with lithium borohydride or borane/dimethyl sulfide furnished four enantiomerically highly enriched dimethylpentan‐5‐olides, which are versatile chiral intermediates.
Monodisperse Dialkoxy‐Substituted Oligo(phenyleneethenylene)s
Authors: Stalmach Ulf , Kolshorn Heinz , Brehm Isabella , Meier Herbert 
Published: June 2010

AbstractIndividual but connected synthetic routes for the preparation of the all‐E‐configured 2,5‐dipropoxy‐substituted oligo(1,4‐phenyleneethenylene)s 1a–g were developed. An increasing number of conjugated stilbene units from n = 1 to n = 11 led to a convergent bathochromic shift (Δλ = λ∞ − λ1 = 127 nm) in the UV/Vis absorption. An exponential function for the convergence of the absorption energies (wavelengths) in conjugated systems is proposed. By a simple extrapolation of this function the effective chain length may be determined.
Electron microscopic observations of Pseudomonas aeruginosa
Authors: Baechler C. A. , Berk R. S. 
Published: June 2010

AbstractPreparative techniques were developed for the purpose of visualizing, by negative contrast, some of the cytological characteristics of unsectioned cells of Pseudomonas aeruginosa. Concentrated fimbriae free from cells had a length of approximately 1.5 μm and a diameter of 6 nm. Pyocin‐like structures ranging in length from 32‐64 nm with a width of 8.6 nm were “attached” to the terminal ends of a small percentage of these fimbriae. Microtubules and ringlets having a diameter of 10‐20 nm were also visualized in the bacteria. Budding or evagination of cell wall material in multiple units up to 135 nm in length was frequently observed in older cultures grown on agar media.
Some physical and chemical parameters affecting the formation and retention of glutamate pools in a marine psychrophilic bacterium
Authors: Griffiths R. P. , Baross J. A. , Hanus F. J. , Morita R. Y. 
Published: June 2010

AbstractThe release of glutamic acid from the obligate marine psychrophilic bacterium Vibrio marinus MP‐1 under various physical conditions has shown that at least two glutamate pools are potentially present. One, designated amino acid pool one, is loosely bound to the cell and is not found in cells accumulating glutamate by de novo synthesis. The second amino acid pool is more stable and is present in cells that are grown on a minimal salts‐sugar medium.
Mutagenic action of methyl methane sulphonate on the bluegreen alga Anacystis nidulans
Authors: Kumar H. D. 
Published: June 2010

AbstractGrowth of the blue‐green alga Anacystis nidulans treated with methyl methane sulphonate (MMS) at pH 5 or 6 was better than that at pH 7 or 8, both in regard to the duration of the lag‐phase and the growth rate. Toxicity of MMS was directly proportional to the temperature at which the cells had been treated. Growth of cells incubated at 5000 lux during MMS treatment was better than those that had been treated in the dark or at 15000 lux.Ten successive treatments with MMS were ineffective in significantly shortening the lagphase of treated cells.The frequency of ultraviolet‐resistant mutants but not of streptomycin‐resistant mutants was substantially increased following single treatment with MMS of 40‐60 minute duration; treatments of longer duration resulted in a steep fall in the number of mutants suggesting thereby that treatments of up to 60 min induce genetic changes which are largely unaccompanied by physiological damage.
Fertilitätsmutanten des Turimycin‐Bildners Streptomyces hygroscopicus IMET JA 6599
Authors: Eritt Inge , Schumann G. , Fleck W. F. 
Published: June 2010

AbstractIn a continuing search for fertility mutants of the turimycin‐producer, Streptomyces hygroscopicus, strain IMET JA 6599, from more than 683 pairs of auxotrophic mutants 19 pairs were found to develop colonies after replica plating on selective media. The frequency of recombinant production in mixed cultures on complex medium varies from 10−6 to 10−2 in different combinations of S. hygroscopicus mutants. Typical frequencies representing the proportion of recombinant colonies from spores and/or fragments of substrate mycelium) and a visual indication of the different fertility levels using the familiar fertility test method are given in Tables and Figures. Additionally, reversion rates of markers and different types of colonies of fertility mutants used in some S. hygroscopicus crosses will be shown.
Ultrastructural alterations at the cell wall and plasma membrane of Candida spec. H induced by n‐alkane assimilation
Authors: Fischer W. , Brückner B. , Meyer H. W. 
Published: June 2010

AbstractThe ultrastructure of n‐alkane‐grown cells of Candida spec. H was investigated by thin sectioning and freeze‐etching techniques. On the plasma membrane shallow depressions could be observed. n‐Alkane deposits were localized within the cell wall and at the plasma membrane. Periplasmic multilamellar structures appear in connection with n‐alkane accumulation. Their participation in hydrocarbon assimilation and the nature of the lamellar structures are discussed.
Dependence of the mycelial growth pattern on the individually regulated cell cycle in Streptomyces granaticolor
Authors: Kretschmer S. 
Published: June 2010

AbstractThe growth behaviour of Streptomyces granaticolor ETH 7437 was studied by the microculture technique. The kinetics of growth and branching were recorded and, since elongation was found to be restricted to apical elongation sites (e‐sites), the rate of elongation per site (α) was determined as well. The mycelia grew exponentially. Initially the growth was dependent on α of the germ tube, but after the start of branching, growth paralleled the exponential increase of the number of branches while α attained a constant average value.Further, for liquid grown mycelia shown about the same growth kinetics the cellular structure was determined after cell wall staining. Three types of cells could be distinguished: apical branchless cells (20%), non‐apical branchless cells (20%) and non‐apical cells with one branch each (60%). Since both the apical and the branched cells possessed an e‐site, 80% of the cells must have been growing at the time of sampling.Combining detailed data obtained from both the alive and the stained mycelia a model was elaborated, which may reflect the events taking place on the cellular level during mycelial growth. The model is based on the assumption that each cell behaves as an independent unity with respect to its cell cycle. But, in contrast to the behaviour of single cell bacteria, in mycelia the two daughter cells formed upon division are neither equivalent nor uniform. Here, the sister cells differ in length, shape and possession of an e‐site. Only one of the daughter cells receives the e‐site of the mother cell, while the other starts its own cell cycle by generating a new e‐site at the cylindrical part of its envelope. Regarding the length of sister cells the degree of heterogeneity increases with the age of the corresponding region of the mycelium, and eventually some cells lose the ability to generate an e‐site, i. e. to grow.With this model the kinetic and structural peculiarities of the mycelial growth of Streptomyces granaticolor can be explained.
Production of glucose isomerase by genus Streptomyces
Authors: Suekane M. , Iizuka H. 
Published: June 2010

AbstractScreening for glucose isomerases was done using 46 species and 63 strains of Streptomyces type cultures. Glucose isomerase was found in a wide range of these species. The intracellular glucose isomerase of S. olivochromogenes showed the highest fructose conversion ratio. The apparent extracellular glucose isomerase activities were observed for several strains of Streptomyces, Streptomyces venezuelae had the highest apparent extracellular glucose isomerase activity.The glucose isomerase yield was improved from 1.95 units/ml to 7.5 units/ml by induced mutation and culturing condition studies. This increase isomerase yield has made it possible to produce glucose isomerase industrially.
Effect of temperature on chlorophyll stability of some subaerial blue‐green algae
Authors: Tripathi S. N. 
Published: June 2010

AbstractChlorophyll stability index of eight subaerial blue‐green algal species, collected from their natural habitats, i.e., bark of trees, soil and roof‐tops and from cultures, has been determined. The algae from natural habitats showed greater chlorophyll stability compared to those algae from cultures. Among the natural algae, high chlorophyll stability was observed in the algae inhabiting adverse habitats. A slight modification in the method of MURTY and MAJUMDER (1962) for determination of chlorophyll stability index has been made. Here the total percentage loss in the amount of Chl a of heated sample in relation to its unheated sample has been considered as chlorophyll stability index.
Non‐invasive time‐course imaging of apoptotic cells by confocal Raman micro‐spectroscopy
Authors: Zoladek Alina , Pascut Flavius C. , Patel Poulam , Notingher Ioan 
Published: June 2010

AbstractConfocal Raman micro‐spectroscopy (CRMS) was used to measure time‐course spectral images of live cells undergoing apoptosis without using molecular labels or other invasive procedures. Human breast cancer cells (MDA‐MB‐231) were exposed to 300 µM etoposide to induce apoptosis, and Raman spectral images were acquired from the same cells at 2‐h intervals over a period of 6 h. The purpose‐built inverted confocal Raman micro‐spectrometer integrated an environmental enclosure and wide‐field fluorescence imaging. These key instrumental elements allowed the cells to be maintained under sterile physiological conditions (37 °C, 5% CO2) and enabled viability and apoptosis assays to be carried out on the cells at the end of CRMS measurements. The time‐course spectral images corresponding to DNA Raman bands indicated an increase in signal intensity in apoptotic cells, which was attributed to DNA condensation. The Raman spectral images of lipids indicated a high accumulation of membrane phospholipids and highly unsaturated non‐membrane lipids in apoptotic cells. This study demonstrates the potential of CRMS for label‐free time‐course imaging of individual live cells. This technique may become a useful tool for in vitro toxicological studies and testing of new pharmaceuticals, as well as other time‐dependent cellular processes, such as cell differentiation, cell cycle and cell–cell interactions. Copyright © 2010 John Wiley & Sons, Ltd.