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Ring Contraction (ring + contraction)
Selected AbstractsRing Contraction of 3,6-Dihydro-2H -thiopyrans to Thiolanes by an Iodo-Oxyacylation ReactionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2004Andre C. B. Lucassen Abstract Reaction of functionalized 3,6-dihydro-2H -thiopyrans with N -iodosuccinimide in the presence of carboxylic acids results in the stereospecific formation of poly-functionalised thiolanes in good yield. The formation of these thiolanes is believed to proceed through either a nucleophilic or an electrophilic pathway leading to 4,5- cis -substituted derivatives. The use of unsymmetrical 2,2-substituted 3,6-dihydro-2H -thiopyrans gave mixtures of isomers that could be separated in several cases. From a 3-substituted thiopyran a 2,2,3,4,5-pentasubstituted thiolane was obtained. Attempts to use alcohols as external nucleophiles were unsuccessful with NIS, NBS, and N -bromoacetamide. Iodo-azidination with in situ generated IN3 was also unsuccessful. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of the Cyclopentyl Nucleoside (,)-Neplanocin A from D -Glucose via Zirconocene-Mediated Ring ContractionHELVETICA CHIMICA ACTA, Issue 6 2005Two approaches for the conversion of d- glucose to (,) -neplanocin A (2), both based on the zirconocene-promoted ring contraction of a vinyl-substituted pyranoside, are herein evaluated (Scheme,1). In the first pathway (Scheme,2), the substrate possesses the , - d- allo configuration (see 6) such that ultimate introduction of the nucleobase would require only an inversion of configuration. However, this precursor proved unresponsive to Cp2Zr (=[ZrCl2(Cp)2]), an end result believed to be a consequence of substantive nonbonded steric effects operating in a key intermediate (Scheme,5). In contrast, the C(2) epimer (see 7) experienced the desired metal-promoted conversion to an enantiomerically pure polyfunctional cyclopentane (see 5 in Scheme,3). The substituents in this product are arrayed in a manner such that conversion to the target nucleoside can be conveniently achieved by a double-inversion sequence (Scheme,4). Recourse to palladium(0)-catalyzed allylic alkylation did not provide an alternate means of generating 2. [source] A Concise Synthesis of Highly Functionalized ,,,-Unsaturated ,-Butyrolactones Through Ring Contraction of 2H-Pyran-2-ones.CHEMINFORM, Issue 46 2004Diptesh Sil Abstract For Abstract see ChemInform Abstract in Full Text. [source] Ring Contraction in Reactions of 3-Benzoylquinoxalin-2-ones with 1,2-Phenylenediamines.CHEMINFORM, Issue 37 2004Benzoimidazole Rearrangement., Quinoxaline Abstract For Abstract see ChemInform Abstract in Full Text. [source] The Effect of Protecting Groups on Thallium(III)-Promoted Ring Contraction of 3-Alkenols.CHEMINFORM, Issue 39 2002Helena M. C. Ferraz Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Novel Ring Contraction of 3-Hydroxy-2,4(1H,3H)-quinolinediones in Aqueous Alkali.CHEMINFORM, Issue 5 2002The First Convenient Route to 2-Hydroxyindoxyls. Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Thallium Trinitrate-Mediated Ring Contraction of 1,2-Dihydronaphthalenes: An Approach to the Synthesis of Indans.CHEMINFORM, Issue 24 2001Helena M. C. Ferraz Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Synthesis and Reactivity of 23 - tert -Butyl- and 23 -Phenyltetraarylazuliporphyrins: an Analysis of the Effect of Bulky Substituents on Oxidative Ring Contractions to Benzocarbaporphyrins,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2007Jessica A. El-Beck Abstract 6- tert -Butyl- and 6-phenylazulene reacted with pyrrole and benzaldehyde in a molar ratio of 1:3:4 in the presence of BF3·Et2O in chloroform, followed by oxidation with DDQ, to give 23 -substituted tetraphenylazuliporphyrins in 15,20,% yield. Slightly higher yields of the related meso -tetrakis(4-chlorophenyl)azuliporphyrins were obtained using 4-chlorobenzaldehyde. The presence of an electron-donating tert -butyl substituent increased the diatropic character of the azuliporphyrin system as determined by the proton NMR chemical shifts for the internal CH resonance, while intermediary results were noted for 23 -phenylazuliporphyrins. Addition of TFA afforded dications with increased aromatic ring currents, but electron-donating substituents (tBu,>,Ph) again produced a larger upfield shift for the internal CH signal due to stabilization of the tropylium character that is required so that the system can attain carbaporphyrin-type aromaticity. The substituted azuliporphyrins reacted with nickel(II) acetate or palladium(II) acetate to give the corresponding organometallic derivatives. In addition, oxidations with tBuOOH and KOH afforded benzocarbaporphyrin products in approximately 50,% yield. The presence of tert -butyl or phenyl substituents did not block these oxidative ring contraction processes, and the rate of reaction was slightly increased compared to 23 -unsubstituted azuliporphyrins. The major products were 22 - tert -butyl or phenyl-substituted benzocarbaporphyrins and minor products with an additional formyl substituent were also isolated. These products are consistent with an initial nucleophilic addition occurring at the position adjacent to the R group on the azulene ring. Detailed mechanisms are proposed to explain these observations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Decarboxylative Ring Contractions and Olefin Insertions of Vinyl Oxazinanones.CHEMINFORM, Issue 47 2006Chao Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] ChemInform Abstract: Ring Contractions of 4-Oxoquinolizine-3-diazonium Tetrafluoroborates, by an Aza Wolff Rearrangement, to Alkyl Indolizine-3-carboxylates.CHEMINFORM, Issue 17 2002Simon Recnik Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Myosin localization during meiosis I of crane-fly spermatocytes gives indications about its role in divisionCYTOSKELETON, Issue 2 2003Rosalind V. Silverman-Gavrila Abstract We showed previously that in crane-fly spermatocytes myosin is required for tubulin flux [Silverman-Gavrila and Forer, 2000a: J Cell Sci 113:597,609], and for normal anaphase chromosome movement and contractile ring contraction [Silverman-Gavrila and Forer, 2001: Cell Motil Cytoskeleton 50:180,197]. Neither the identity nor the distribution of myosin(s) were known. In the present work, we used immunofluorescence and confocal microscopy to study myosin during meiosis-I of crane-fly spermatocytes compared to tubulin, actin, and skeletor, a spindle matrix protein, in order to further understand how myosin might function during cell division. Antibodies to myosin II regulatory light chain and myosin II heavy chain gave similar staining patterns, both dependent on stage: myosin is associated with nuclei, asters, centrosomes, chromosomes, spindle microtubules, midbody microtubules, and contractile rings. Myosin and actin colocalization along kinetochore fibers from prometaphase to anaphase are consistent with suggestions that acto-myosin forces in these stages propel kinetochore fibres poleward and trigger tubulin flux in kinetochore fibres, contributing in this way to poleward chromosome movement. Myosin and actin colocalization at the cell equator in cytokinesis, similar to studies in other cells [e.g., Fujiwara and Pollard, 1978: J Cell Biol 77:182,195], supports a role of actin-myosin interactions in contractile ring function. Myosin and skeletor colocalization in prometaphase spindles is consistent with a role of these proteins in spindle formation. After microtubules or actin were disrupted, myosin remained in spindles and contractile rings, suggesting that the presence of myosin in these structures does not require the continued presence of microtubules or actin. BDM (2,3 butanedione, 2 monoxime) treatment that inhibits chromosome movement and cytokinesis also altered myosin distributions in anaphase spindles and contractile rings, consistent with the physiological effects, suggesting also that myosin needs to be active in order to be properly distributed. Cell Motil. Cytoskeleton 55:97,113, 2003. © 2003 Wiley-Liss, Inc. [source] Further Studies on the Synthesis of meso -Tetraarylazuliporphyrins under Lindsey,Rothemund Reaction Conditions and Their Conversion into BenzocarbaporphyrinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2003Timothy D. Lash Abstract Azulene has been shown to react with pyrrole and a series of aromatic aldehydes in the presence of boron trifluoride etherate to give meso -tetraarylazuliporphyrins 6. Good yields of azuliporphyrins were obtained for benzaldehyde, 4-chlorobenzaldehyde, 4-bromobenzaldehyde, and 4-iodobenzaldehyde, and under dilute conditions p -tolualdehyde gave respectable yields. In each case, substantial amounts of meso -tetraarylporphyrins were also formed and a minor fraction of carbaporphyrin by-products could be detected, but otherwise no other macrocyclic products could be identified. 4-Nitrobenzaldehyde gave relatively poor yields of the corresponding azuliporphyrin, while p -anisaldehyde only gave trace amounts of product. Pentafluorobenzaldehyde gave variable results, although in this case a large number of additional by-products were identified including N -fused pentaphyrin, hexaphyrin, and higher order porphyrinoids, but no expanded azulene-containing macrocycles could be detected. Azuliporphyrins undergo reversible nucleophilic substitution on the seven-membered ring with pyrrolidine, benzenethiol, hydrazine, or benzylamine to give carbaporphyrin adducts. This property appears to facilitate an oxidative ring contraction of azuliporphyrins 6 with tert -butyl hydroperoxide in the presence of potassium hydroxide to produce mixtures of benzocarbaporphyrins 19 and 20. Tetraaryl-benzocarbaporphyrins exhibit slightly reduced diatropic ring currents compared to their meso -unsubstituted counterparts, although their UV/Vis spectra are very porphyrin-like and exhibit strong Soret bands near 450 nm. The benzocarbaporphyrins undergo reversible protonation to give monocationic and dicationic species. The latter involves C -protonation to generate an internal CH2 within the macrocyclic cavity. X-ray crystallography of tetraphenylbenzocarbaporphyrin 19a confirms that the preferred tautomer has the two NHs on either side of the indene subunit, in agreement with previous theoretical and spectroscopic studies. In addition, the presence of phenyl substituents at the 5,20-positions was found to tilt the indene moiety substantially by 27.4(1)° relative to the [18]annulene substructure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis of the Cyclopentyl Nucleoside (,)-Neplanocin A from D -Glucose via Zirconocene-Mediated Ring ContractionHELVETICA CHIMICA ACTA, Issue 6 2005Two approaches for the conversion of d- glucose to (,) -neplanocin A (2), both based on the zirconocene-promoted ring contraction of a vinyl-substituted pyranoside, are herein evaluated (Scheme,1). In the first pathway (Scheme,2), the substrate possesses the , - d- allo configuration (see 6) such that ultimate introduction of the nucleobase would require only an inversion of configuration. However, this precursor proved unresponsive to Cp2Zr (=[ZrCl2(Cp)2]), an end result believed to be a consequence of substantive nonbonded steric effects operating in a key intermediate (Scheme,5). In contrast, the C(2) epimer (see 7) experienced the desired metal-promoted conversion to an enantiomerically pure polyfunctional cyclopentane (see 5 in Scheme,3). The substituents in this product are arrayed in a manner such that conversion to the target nucleoside can be conveniently achieved by a double-inversion sequence (Scheme,4). Recourse to palladium(0)-catalyzed allylic alkylation did not provide an alternate means of generating 2. [source] Synthesis, structure, reactions, and photoelectron spectra of new mixed sulfur-, selenium- or tellurium and silicon- or tin-containing heterocyclesHETEROATOM CHEMISTRY, Issue 5 2007Eric Block More than 40 new 4- to 12-membered ring heterocycles containing various combinations of Group 14 elements (Si and Sn) and Group 16 elements (S, Se, and Te) have been synthesized and fully characterized. Synthesis of these small-ring as well as medium-ring (mesocyclic) heterocycles from ,, ,-dihalides was facilitated by the presence of gem-dialkylsilyl and gem-dialkylstannyl groups in the precursors. Solid-state conformations of the new ring systems have been determined by X-ray crystallography. Oxidation of mixed S(Se, Te)/Si eight-membered ring mesocycles as well as 1,5-dithia-, 1,5-diselena-, and 1,5-ditelluracyclooctane with NOPF6 gave dications, which can be characterized by NMR. On treatment with nucleophiles, mesocyclic dications or the corresponding radical cations underwent ring contraction to give five- or six-membered ring heterocycles. The ionization energies of the above conformationally constrained ,-disilanyl sulfides and selenides were determined by photoelectron spectroscopy. These ionization energies reflect substantial (0.53--0.75 eV) orbital destabilizations. The basis for these destabilizations was investigated by theoretical calculations, which reveal geometry-dependent interaction between sulfur or selenium lone pair orbitals and ,-orbitals, especially Si,Si ,-orbitals. These results suggest facile redox chemistry for these compounds and significantly extend the concept of ,-stabilization of electron-deficient centers. © 2007 Wiley Periodicals, Inc. 18:509,515, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20333 [source] Retro-ene reactions in heterocyclic synthesis. v. a novel synthetic method for 1,3,5-triazine-2,4(1H,3H)-dionesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2007The Late Kunio Ito N - t -Butylamidines 1 on heating with diphenyl carbonate (2) at 150-180° gave the 1,3,5-triazine-2,4(1H,3H)-dione derivatives 5. Acylation of amidines 1 and cyclocondensation of the resulting carbamates 3 gave [1,3,5,7]tetrazocine-2,6-dione derivatives 4, and subsequent retro-ene reaction and ring contraction afforded triazine derivatives 5. [source] Theoretical study of protonated xylenes: ethene elimination and H,C-scrambling reactionsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2004Bjørnar Arstad Abstract Quantum chemical calculations have been carried out to investigate various unimolecular rearrangements that can take place in protonated gas-phase xylenes. Hydrogen and methyl group ring migrations were investigated. The barriers for hydrogen migrations are lower than the barriers for methyl group migrations. Mechanisms for ring expansion to seven-membered rings, and for contraction to five-membered rings were studied. Both of these mechanisms can eventually lead to ethene elimination. The most favourable ring expansion step goes through a 1,3-hydrogen shift from a methyl group onto the arenium ring, forming a protonated methylcycloheptatriene. Interconversions between various ring-expanded forms have been investigated. Re-contraction can lead to an ethylbenzenium ion that could subsequently split off ethene. Alternatively, the xylenium ion can contract to a five-membered ring. The immediate product is a bicyclic ion (bicyclo[3.1.0]hexane skeleton) that can rearrange further to give an ethylbenzenium ion, or the five-ring system can split off ethene, and be converted into a cyclopentadienyl ion that can isomerize into a benzenium ion. Stable structures and transition states are calculated both at the B3LYP/cc-pVTZ//B3LYP/6-311G(d,p) and at the MP2/cc-pVTZ//MP2/6-31G(d) levels. The energies needed for ring expansion or ring contraction are not very different, and the calculations suggest that both reaction paths are possible, but the energy needed for actually splitting off an ethene molecule is lower along the expansion path. Copyright © 2004 John Wiley & Sons, Ltd. [source] SEPH, a Cdc7p orthologue from Aspergillus nidulans, functions upstream of actin ring formation during cytokinesisMOLECULAR MICROBIOLOGY, Issue 1 2001Kenneth S. Bruno In the filamentous fungus, Aspergillus nidulans, multiple rounds of nuclear division occur before cytokinesis, allowing an unambiguous identification of genes required specifically for cytokinesis. As in animal cells, both an intact microtubule cytoskeleton and progression through mitosis are required for actin ring formation and contraction. The sepH gene from A. nidulans was discovered in a screen for temperature-sensitive cytokinesis mutants. Sequence analysis showed that SEPH is 42% identical to the serine,threonine kinase Cdc7p from fission yeast. Signalling through the Septation Initiation Network (SIN), which includes Cdc7p and the GTPase Spg1p, is emerging as a primary regulatory pathway used by fission yeast to control cytokinesis. A similar group of proteins comprise the Mitotic Exit Network (MEN) in budding yeast. This is the first direct evidence for the existence of a functional SIN,MEN pathway outside budding and fission yeast. In addition to SEPH, potential homologues were also identified in other fungi and plants but not in animal cells. Deletion of sepH resulted in a viable strain that failed to septate at any temperature. Interestingly, quantitative analysis of the actin cytoskeleton revealed that sepH is required for construction of the actin ring. Therefore, SEPH is distinct from its counterpart in fission yeast, in which SIN components operate downstream of actin ring formation and are necessary for ring contraction and later events of septation. We conclude that A. nidulans has components of a SIN,MEN pathway, one of which, SEPH, is required for early events during cytokinesis. [source] Pharmacology and immunological actions of a herbal medicine ASHMITM on allergic asthmaPHYTOTHERAPY RESEARCH, Issue 7 2010Tengfei Zhang Abstract Allergic asthma is a chronic and progressive inflammatory disease for which there is no satisfactory treatment. Studies reported tolerability and efficacy of an anti-asthma herbal medicine intervention (ASHMI) for asthma patients, developed from traditional Chinese medicine. To investigate the pharmacological actions of ASHMI on early- and late-phase airway responses (EAR and LAR), Ovalbumin (OVA)-sensitized mice received 6 weeks of ASHMI treatment beginning 24,h following the first intratracheal OVA challenge. EAR were determined 30,min following the fourth challenge and LAR 48,h following the last challenge. ASHMI effects on cytokine secretion, murine tracheal ring contraction and human bronchial smooth muscle cell prostaglandin (PG) production were also determined. ASHMI abolished EAR, which was associated with significantly reduced histamine, leukotriene C4, and OVA-specific IgE levels, as well as LAR, which was associated with significantly reduced bronchoalveolar lavage fluid (BALF) eosinophils, decreased airway remodeling, and lower Th2 cytokine levels in BALF and splenocyte cultures. Furthermore, ASHMI inhibited contraction of murine tracheal rings and increased production of the potent smooth muscle relaxer PGI2. ASHMI abrogation of allergic airway responses is associated with broad effects on asthma pathological mechanisms. Copyright © 2009 John Wiley & Sons, Ltd. [source] Selegiline, an MAO-B inhibitor, attenuates airway smooth muscle contraction in the rat tracheaJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 7 2004Maki Yoshimura Selegiline is widely used for Parkinson's disease and sometimes for Alzheimer's disease. It is reported to affect intracellular Ca2+ concentration. Since intracellular Ca2+ is partly regulated by phosphatidylinositol (PI) response and is important for smooth muscle contraction, selegiline may affect airway smooth muscle tension. We examined the effects of selegiline on acetylcholine (ACh)- and KCl-induced contractile and PI responses in rat trachea. The trachea was cut into 3-mm-wide ring segments or 1-mm-wide slices. ACh (3 ,M, 50% effective dose) or KCl (40mM) was added, and ring relaxation was induced by the addition of selegiline. Tracheal slices were incubated with [3H]myo -inositol and 3 ,M ACh in the presence of selegiline, and [3H]inositol monophosphate (IP1) was measured. Selegiline dose-dependently attenuated ACh- and KCl-induced tracheal ring contractions. Fifty-percent inhibitory doses (ID50) of selegiline against ACh- and KCl-induced contraction were 120±30 ,M and 80±20 ,M, respectively. Basal and ACh-induced IP1 accumulation were 2.20±0.20 Bq and 7.88±0.23 Bq, respectively, and selegiline at a dose of 1000 ,M attenuated ACh-induced IP1 accumulation (5.44±0.30 Bq). These results suggest that selegiline inhibits contractile responses through the inhibition of voltage-operated Ca2+ channels and the PI response. [source] | ||||||||||||||||