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Precursor Compound (precursor + compound)
Selected AbstractsRole of menaquinone biosynthesis genes in selenate reduction by Enterobacter cloacae SLD1a-1 and Escherichia coli K12ENVIRONMENTAL MICROBIOLOGY, Issue 1 2009Jincai Ma Summary In this study, we investigated the role of menaquinone biosynthesis genes in selenate reduction by Enterobacter cloacae SLD1a-1 and Escherichia coli K12. A mini-Tn5 transposon mutant of E. cloacae SLD1a-1, designated as 4E6, was isolated that had lost the ability to reduce Se(VI) to Se(0). Genetic analysis of mutant strain 4E6 showed that the transposon was inserted within a menD gene among a menFDHBCE gene cluster that encodes for proteins required for menaquinone biosynthesis. A group of E. coli K12 strains with single mutations in the menF, menD, menC and menE genes were tested for loss of selenate reduction activity. The results showed that E. coli K12 carrying a deletion of either the menD, menC or menE gene was unable to reduce selenate. Complementation using wild-type sequences of the E. cloacae SLD1a-1 menFDHBCE sequence successfully restored the selenate reduction activity in mutant strain 4E6, and E. coli K12 menD and menE mutants. Selenate reduction activity in 4E6 was also restored by chemical complementation using the menaquinone precursor compound 1,4-dihydroxy-2-nathphoic acid. The results of this work suggest that menaquinones are an important source of electrons for the selenate reductase, and are required for selenate reduction activity in E. cloacae SLD1a-1 and E. coli K12. [source] 7-Halogenated 7-Deaza-2,-deoxyxanthine 2,-DeoxyribonucleosidesHELVETICA CHIMICA ACTA, Issue 6 2004Frank Seela The synthesis of the 7-halogenated derivatives 1b (7-bromo) and 1c (7-iodo) of 7-deaza-2,-deoxyxanthosine (1a) is described. A partial Br,I exchange was observed when the demethylation of 6-methoxy precursor compound 4b was performed with Me3SiCl/NaI. This reaction is circumvented by the nucleophilic displacement of the MeO group under strong alkaline conditions. The halogenated 7-deaza-2,-deoxyxanthosine derivatives 1b,c show a decreased S -conformer population of the sugar moiety compared to the nonhalogenated 1a. They are expected to form stronger triplexes when they replace 1a in the 1,dA,dT base triplet. [source] 2-Amino-3-methyl-6-[methyl(phenyl)amino]-5-nitropyrimidin-4(3H)-one: polarized molecules within hydrogen-bonded sheetsACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2009Ricaurte Rodríguez The pyrimidinone ring in the title compound, C12H13N5O3, is effectively planar, despite the presence of five substituents. The bond distances provide evidence for significant polarization of the electronic structure, with charge separation, and the molecules are linked into sheets by a combination of N,H...O and N,H...,(arene) hydrogen bonds. Comparisons are made with the molecular and supramolecular structures of the precursor compound 2-amino-6-[methyl(phenyl)amino]-5-nitropyrimidin-4(3H)-one. [source] Self-Assembly of a Triangle-Shaped, Hexaplatinum-Incorporated, Supramolecular Amphiphile in Solution and at InterfacesCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2009Umamageswaran Maran Dr. Abstract The self-assembly and characterization of a novel supramolecular amphiphile built from a new 60° amphiphilic precursor that incorporates hydrophilic platinum(II) metals and hydrophobic dioctadecyloxy chains is reported. The amphiphilic macrocycle and its precursor compound have been characterized by multinuclear NMR spectroscopy, ESI-MS, and other standard techniques. The coacervate morphology of the amphiphile at the liquid,liquid interface has been studied by using confocal optical microscopy and in situ Raman spectroscopy. The self-assembly of the amphiphilic macrocycle at the air,water interface has been investigated through Langmuir-trough techniques. The study indicates the possible formation of surface micelle-like aggregates. The disparity between the experimental molecular areas and those derived from molecular models support the idea of aggregation. AFM images of the surface aggregates show the formation of a flat topology with arbitrary ridgelike patterns. Reasonable molecular-packing arrangements are proposed to explain the molecular organization within the observed structures. [source] O -Acylated 2-Phosphanylphenol Derivatives , Useful Ligands in the Nickel-Catalyzed Polymerization of EthyleneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2009Dmitry G. Yakhvarov Abstract The title ligands were prepared by O -acylation of 2-diphenylphosphanyl-4-methylphenol (1) or directly by double lithiation of 2-bromo-4-methylphenol and stepwise coupling with ClPPh2 and ClP(O)Ph2 or RC(O)Cl (R = Me, tBu, Ph, 4-MeOC6H4) to afford diphenylphosphinate 2 and carboxylic esters 3a,d. X-ray crystal structure analyses of 3b,d show conformations in which the P -phenyl substituents are rotated away from the ester group and the C(O)O , planes are nearly perpendicular to the phenol ring , plane. O -Acylated phosphanylphenols 2 and 3a,d form highly active catalysts with Ni(1,5-cod)2 (as does 1) for polymerization of ethylene, whereas phosphanylphenyl ethers do not give catalysts under the same conditions. The reason is the cleavage of the O -acyl bond upon heating with nickel(0) precursor compounds in the presence of ethylene. The precursors are P-coordinated Ni0 complexes, which are formed at room temperature, such as 4d obtained from 3d and Ni(cod)2 (in a 2:1 molar ratio), and characterized by multinuclear NMR spectroscopy. Upon heating in the presence of ethylene, the precatalysts are activated. Catalysts 2Ni and 3a,dNi convert ethylene nearly quantitatively, 2Ni slowly, and 3a,dNi rapidly, into linear polyethylene with vinyl and methyl end groups, and in the latter case, C(O)R end groups are also detectable. This proves insertion of Ni0 into the O,C(O)R bond of 3a,d ligands for formation of the primary catalyst. Termination of the first chain growing cycle by ,-hydride elimination changes the mechanism to the phosphanylphenolate,NiH initiated polymerization providing the main body of the polymer. A small retardation in the ethylene consumption rate with 3a,dNi catalysts relative to that observed for 1Ni and stabilization of the catalyst, which gives rise to reproducibly high ethylene conversion, is observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Heterobimetallic Systems Containing Organometallic and Classical Coordination Sites: Effects of Subtle Changes in the Werner-Type SiteEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2005Tianlu Sheng Abstract Several highly unsymmetrical heterodinuclear Mn/Zn complexes are reported, in which an organometallic CpMn-(CO)2 fragment and a classical Werner-type zinc coordination unit are arranged in close proximity by means of a bridging pyrazolate. Ligand scaffolds differing in the chelate size of the tripodal tetradentate {N4} binding site, and different coligands for zinc are employed. Both the zinc-devoid precursor compounds and the bimetallic complexes with zinc(II) nested in the tris(pyridylalkyl)amine type {N4} compartment have been characterized by X-ray crystallography. Structural and spectroscopic features as well as the redox potentials of the MnI/MnII couple indicate slight effects of the redox-inactive Werner-type subunit on the properties of the organometallic site. Oxidation is highly localized at the organometallic manganese site, as is evidenced by IR and EPR spectroscopy and supported by DFT calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] The role of cysteine and cysteine,S conjugates as odour precursors in the flavour and fragrance industry ,FLAVOUR AND FRAGRANCE JOURNAL, Issue 6 2008Christian Starkenmann Abstract Volatile sulphur compounds are important odorants in the flavour and fragrance industries. Recent developments in the field have reinvigorated sulphur compound research, particularly with regard to the precursor compounds of volatile thiols. The present review concentrates on the role of cysteine and cysteine,S conjugates as precursor compounds for a variety of aromas and examines the chemical and enzymatic pathways of degradation and biotransformation. Cysteine is an important source of sulphur in flavour chemistry and may be degraded into hydrogen sulphide, which can further participate in other reactions. Direct reactions of cysteine and the pathways particular to various flavours and fragrances are discussed, with an emphasis on the precursor compounds cysteine,S conjugates. The importance of cysteine precursors in plants, including onion, wine, passion fruit, bitter orange, asparagus and bell pepper and the formation of natural scents in cats and humans are discussed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Diastereo- and Enantioselective Intramolecular [2+2],Photocycloaddition Reactions of 3-(,,-Alkenyl)- and 3-(,,-Alkenyloxy)-Substituted 5,6-Dihydro-1H -pyridin-2-onesCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2010Dominik Albrecht Dr. Abstract 3-(,,-Alkenyl)-substituted 5,6-dihydro-1H -pyridin-2-ones 2,4 were prepared as photocycloaddition precursors either by cross-coupling from 3-iodo-5,6-dihydro-1H -pyridin-2-one (8) or,more favorably,from the corresponding ,-(,,-alkenyl)-substituted ,-valerolactams 9,11 by a selenylation/elimination sequence (56,62,% overall yield). 3-(,,-Alkenyloxy)-substituted 5,6-dihydro-1H -pyridin-2-ones 5 and 6 were accessible in 43 and 37,% overall yield from 3-diazopiperidin-2-one (15) by an ,,,-chloroselenylation reaction at the 3-position followed by nucleophilic displacement of a chloride ion with an ,-alkenolate and oxidative elimination of selenoxide. Upon irradiation at ,=254,nm, the precursor compounds underwent a clean intramolecular [2+2] photocycloaddition reaction. Substrates 2 and 5, tethered by a two-atom chain, exclusively delivered the respective crossed products 19 and 20, and substrates 3, 5, and 6, tethered by longer chains, gave the straight products 21,23. The completely regio- and diastereoselective photocycloaddition reactions proceeded in 63,83,% yield. Irradiation in the presence of the chiral templates (,)- 1 and (+)- 31 at ,75,°C in toluene rendered the reactions enantioselective with selectivities varying between 40 and 85,%,ee. Truncated template rac - 31 was prepared as a noranalogue of the well-established template 1 in eight steps and 56,% yield from the Kemp triacid (24). Subsequent resolution delivered the enantiomerically pure templates (,)- 31 and (+)- 31. The outcome of the reactions is compared to the results achieved with 4-substituted 5,6-dihydro-1H -pyridin-2-ones and quinolones. 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