bluuebunny/crossref_metadata_2025_split huggingface dataset:
Insertion of Alkynes into the PtSi Bond of Silylplatinum Complexes Leading to the Formation of 4‐Sila‐3‐platinacyclobutenes and 5‐Sila‐2‐platina‐1,4‐cyclohexadienes
Authors: Tanabe Makoto , Osakada Kohtaro 
Published: January 2004

AbstractThe reaction of dimethyl acetylenedicarboxylate (DMAD) with [Pt(SiHPh2)2(PMe3)2] produces cis‐[Pt(CZCZSiHPh2)(SiHPh2)(PMe3)2] (cis‐1, Z = COOMe) and [Pt(CZCZSiPh2)(PMe3)2] (2) depending on the reaction conditions. cis‐1 and 2 are equilibrated in solution at room temperature, and they are isolated by recrystallization of the mixtures. cis‐1 is converted slowly in solution into trans‐[Pt(CZCZSiHPh2)(SiHPh2)(PMe3)2] (trans‐1) via intermediate 2 followed by reaction with H2SiPh2. DMAD also reacts with [Pt(SiHPh2)2(dmpe)] (dmpe = 1,2‐bis(dimethylphosphino)ethane) to afford [Pt(CZCZSiHPh2)(SiHPh2)(dmpe)] (3). Conversion of 3 into 4‐sila‐3‐platinacyclobutene [Pt(CZCZSiPh2)(dmpe)] (4) takes place, accompanied by formation of H2SiPh2, to give an equilibrated mixture of the two complexes. Crystallographic and spectroscopic data of cis‐1, trans‐1, and 3 suggest the presence of an intramolecular interaction between the SiH group of the 3‐sila‐1‐propenyl ligand and Pt via an SiHPt three‐center‐four‐electron bond in the solid state and in solution. DMAD reacts with 2 to give 5‐sila‐2‐platina‐1,4‐cyclohexadiene with π‐coordinated DMAD, [Pt(CZCZSiPh2CZCZ)(DMAD)(PMe3)2] (5), which is also obtained from the reaction of excess DMAD with [Pt(SiHPh2)2(PMe3)2]. Unsymmetrical six‐membered silaplatinacycles without π‐coordinated alkyne, [Pt(CZCZSiPh2CHCX)(PMe3)2] (6: X = COOMe; 7: X = Ph), are prepared analogously from the respective reactions of phenyl acetylene and of methyl acetylene carboxylate with 2. Methyl 2‐butynolate reacts with 2 at 50 °C to form a mixture of the regioisomers [Pt(CZCZSiPh2CMeCZ)(PMe3)2] (8) and [Pt(CZCZSiPh2CZCMe)(PMe3)2] (9).
Palladium‐Catalyzed Cross‐Coupling Reactions of Amines with Alkenyl Bromides: A New Method for the Synthesis of Enamines and Imines
Authors: Barluenga José , Fernández M. Alejandro , Aznar Fernando , Valdés Carlos 
Published: January 2004

AbstractThe palladium‐catalyzed cross‐coupling reaction of alkenyl bromides with secondary and primary amines gives rise to enamines and imines, respectively. This new transformation expands the applicability of palladium‐catalyzed CN bond forming reactions (the Buchwald–Hartwig amination), which have mostly been applied to aryl halides. After screening of different ligands, bases, and solvents, the catalytic combination [Pd2(dba)3]/BINAP in the presence of NaOtBu in toluene gave the best results in the cross‐coupling of secondary amines with 1‐bromostyrene (dba=dibenzylideneacetone, BINAP=2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl). The corresponding enamines are obtained cleanly and in nearly quantitative yields. However, steric hindrance seems to be a limitation of the reaction, as amines carrying large substituents are not well converted. The same methodology can be applied to the coupling of secondary amines with 2‐bromostyrene. Moreover, the reaction with substituted 2‐bromopropenes allows regioselective synthesis of isomerizable terminal enamines without isomerization of the double bond. The best catalytic conditions for the cross‐coupling of 1‐bromostyrene with primary amines include again the use of the Pd0/BINAP/NaOtBu system. The reaction gives rise to the expected imines in very short times and with low catalyst loadings. A set of structurally diverse imines can be prepared by this methodology through variations in the structure of both coupling partners. However, 2‐bromostyrene failed to give good results in this coupling reaction, probably due to product inhibition of the catalytic cycle. Competition experiments of vinyl versus aryl amination reveal that the reaction occurs preferentially on vinyl bromides.
Evidence That Protons Can Be the Active Catalysts in Lewis Acid Mediated Hetero‐Michael Addition Reactions
Authors: Wabnitz Tobias C. , Yu Jin‐Quan , Spencer Jonathan B. 
Published: January 2004

AbstractThe mechanism of Lewis acid catalysed hetero‐Michael addition reactions of weakly basic nucleophiles to α,β‐unsaturated ketones was investigated. Protons, rather than metal ions, were identified as the active catalysts. Other mechanisms have been ruled out by analyses of side products and of stoichiometric enone–catalyst mixtures and by the use of radical inhibitors. No evidence for the involvement of π‐olefin–metal complexes or for carbonyl–metal‐ion interactions was obtained. The reactions did not proceed in the presence of the non‐coordinating base 2,6‐di‐tert‐butylpyridine. An excellent correlation of catalytic activities with cation hydrolysis constants was obtained. Different reactivities of mono‐ and dicarbonyl substrates have been rationalised. A 1H NMR probe for the assessment of proton generation was established and Lewis acids have been classified according to their propensity to hydrolyse in organic solvents. Brønsted acid‐catalysed conjugate addition reactions of nitrogen, oxygen, sulfur and carbon nucleophiles are developed and implications for asymmetric Lewis acid catalysis are discussed.
Enantioselective Synthesis of Non‐Natural Aromatic α‐Amino Acids
Authors: Krebs Andreas , Ludwig Verena , Pfizer José , Dürner Gerd , Göbel Michael W. 
Published: January 2004

AbstractWe present two complementary methods for the stereoselective synthesis of non‐natural α‐amino acids with aromatic or heteroaromatic side chains. One approach is based on the chemical transformation of methionine, whereas the other applies the stereoselective Myers alkylation of glycine. The resulting product types differ in the linker length between glycine and the aromatic substituent. Since methionine and pseudoephedrine are available in both absolute configurations, R‐ or S‐configured enantiopure amino acids with either C2 or C3 linkers can be obtained on gram scales. In each case the key step of the synthesis is hydroboration of the unsaturated building blocks 9 and 17, followed by palladium‐catalyzed Suzuki cross‐coupling with aryl halides. Attention must in certain cases be paid to the stereochemical integrity when basic Suzuki conditions are applied. Our initial difficulties are reported as well as the final “racemization‐proof” procedures. The protecting groups chosen for the α‐amino acids should be compatible with solid‐phase peptide synthesis. This was confirmed by the successful synthesis of a series of tripeptides.
Extension of Conjugation Leading to Bathochromic or Hypsochromic Effects in OPV Series
Authors: Meier Herbert , Gerold Jürgen , Kolshorn Heinz , Mühling Bastian 
Published: January 2004

AbstractFour OPV series 1–4 (a–d) with a terminal dialkylamino group as electron donor were prepared by Wittig–Horner reactions. To study the influence of the push–pull effect on the long‐wavelength absorption, three of the four series contained terminal acceptor groups (CN, CHO, NO2). The length of the chromophores strongly affects the intramolecular charge transfer (ICT)—an effect which superimposes upon the extension of the conjugation. Increasing numbers n of repeat units cause an overall bathochromic shift for the purely donor‐substituted series 1 a–4 a and the series 1 b–4 b with CN as weak acceptor. The two effects annihilate each other in the series 1 c–4 c with terminal CHO groups, so that the absorption maxima are almost independent of the length of the chromophore. A hypsochromic shift is observed for the series 1 d–4 d, which contains the strong acceptor group NO2. This anomaly disappears on protonation of the dialkylamino group because the push–pull effect disappears in the ammonium salts. The results can be explained by semiempirical quantum mechanics (AM1, INDO/S). The HOMO–LUMO transition, which is mainly responsible for the ICT, becomes less important in the electron transitions S0→S1 when the distance between donor and acceptor is increased. The commonly used VB model, which contains an electroneutral and a zwitterionic resonance structure, is contrasted with a MO model with dipole segments at both ends of the OPV chains. The latter model turned out to be more appropriate—at least for donor–acceptor‐substituted OPVs with n ≥ 2.
First Structural Characterization of Binary AsIIIand SbIIIAzides
Authors: Haiges Ralf , Vij Ashwani , Boatz Jerry A. , Schneider Stefan , Schroer Thorsten , Gerken Michael , Christe Karl O. 
Published: January 2004

AbstractThe highly explosive molecules As(N3)3and Sb(N3)3were obtained in pure form by the reactions of the corresponding fluorides with (CH3)3SiN3in SO2and purification by sublimation. The crystal structures and14N NMR, infrared, and Raman spectra were determined, and the results compared to ab initio second‐order perturbation theory calculations. Whereas Sb(N3)3possesses a propeller‐shaped, pyramidal structure with perfectC3symmetry, the As(N3)3molecule is significantly distorted fromC3symmetry due to crystal packing effects.
Interactions Between Organic Molecules and Water: Rotational Spectrum of the 1:1 Oxetane–Water complex
Authors: Ottaviani Paolo , Giuliano Michela , Velino Biagio , Caminati Walther 
Published: January 2004

AbstractThe 1:1 molecular complex between oxetane and water has been investigated by using free‐jet millimeter‐wave spectroscopy. The rotational spectra of five isotopomers (with H2O, D2O, DOH, HOD and H218O) have been assigned. Partial r0 and rs structures of the complex have been derived. The water moiety lies in the plane of symmetry of oxetane, with the “free” hydrogen E with respect to the ring. The oxetane ring appears to be slightly nonplanar, with the Cβ carbon tilted on the opposite side of the water unity. The three atoms involved in the hydrogen bond adopt a linear arrangement with an Oring⋅⋅⋅H distance of about 1.86 Å, and the angle between the COC bisector and the Oring⋅⋅⋅H bond being ≅106°. Additionally, quantum‐chemical calculations for the complex were performed and were found to be in agreement with the experimental results.
Enzyme‐catalyzed hydrolysis of 18‐methyl eicosanoic acid‐cysteine thioester
Authors: Ganske Franka , Meyer Hartmut H. , Deutz Herbert , Bornscheuer Uwe 
Published: January 2004

Abstract18‐Methyleicosanoic acid (18‐MEA) is the major fatty acid component linked by a cysteine thioester bond within the cuticle at the surface of hair of humans and animals. An excess of 18‐MEA results in fatty hair and a mild method for enzymatic removal was investigated using a range of commercially available hydrolases. Pure 18‐MEA is available from natural sources only in μg quantities, so it was synthesized in gram‐amounts in a 7‐step chemical synthesis at an overall yield of 34%. Starting from 18‐MEA the corresponding thioester with cysteine (Cys‐18‐MEA) serving as model compound was obtained at a yield of 85%. The detection of hydrolases acting on Cys‐18‐MEA was performed using Ellmanns reagent followed by spectrophotometric quantification of 5‐thio‐2‐nitrobenzoic acid at 410 nm. This led to the identification of 6 enzymes with lipase from Pseudomonas cepacia (Amano PS) as the most active one. With Amano PS, 60% conversion of Cys‐18‐MEA was achieved within 5 h‐reaction time at 30 °C. Preliminary results using samples of human hair were also performed and showed that hydrolytic activity is detectable after incubation of the hair with Amano PS.
The role of pancreatic lipase C2‐like domain in enzyme interaction with a lipid‐water interface
Authors: Chahinian Henri , Belle Valérie , Fournel André , Carrière Frédéric 
Published: January 2004

AbstractHuman pancreatic lipase (HPL) consists of two functional domains: an N‐terminal catalytic domain (N‐HPL), and a β‐sandwich C‐terminal domain (C‐HPL) involved in the binding process between HPL and colipase. Structural similarities between C‐HPL and C2 domains have suggested another function in lipase‐lipid interactions. C2 domains occur in a wide range of proteins involved in phospholipid interactions, in signal transduction (phosphoinositide‐specific phospholipase C, protein kinase C, cytosolic phospholipase A2), membrane traffic (synaptotagmin I, rabphilin), and membrane disruption (perforin).In this paper, we review experiments supporting an absolute requirement of C‐HPL for interfacial binding of HPL. N‐HPL and C‐HPL were produced as individual polypeptides, and their partitioning between the water phase and a lipid interface was assessed using trioctanoin emulsions or the monomolecular film technique. Using monoclonal antibodies and site‐directed mutagenesis, the contribution to lipase‐lipid interactions of an exposed hydrophobic loop (β5') present in C‐HPL was investigated. The β5' loop is located on the same side of HPL as the hydrophobic loops surrounding the active site, and has the same topology as the CBR3 loop found in C2 domains. Based on structural homology between C‐HPL and C2 domains, a model of HPL orientation at a lipid interface is proposed.
An integrated microbial/enzymatic process for production of rhamnolipids and L‐(+)‐rhamnose from rapeseed oil with Pseudomonas sp. DSM 2874
Authors: Trummler Klaus , Effenberger Franz , Syldatk Christoph 
Published: January 2004

AbstractThe object of this paper is the development of a biotechnological process for production of rhamnolipids by Pseudomoas sp. DSM 2874. The product obtained from rapeseed oil was found to be a mixture of up to four glycolipids (rhamnolipid 1 ‐ 4), L‐(+)rhamnose and (R, R)‐3‐(3‐hydroxydecanoyloxy) decanoic acid. An HPLC‐method was developed for identification and quantification of rhamnolipids and fatty acids, using an evaporative light scattering detector. Growing cells under nitrogen limiting conditions and resting cells were used for rhamnolipid production with triglycerides as C‐source. Best results and product yields (up to 45 g l‐1 of mixtures of rhamnolipid 1 and rhamnolipid 3) were obtained using resting cells in a fed batch process with rapeseed oil as C‐source. Product composition was found to be strongly dependent on the process conditions. Using the fungal enzyme Naringinase it was possible to cleave the glycosidic bond between the two rhamnose units of rhamnolipid 3, and the bond between L‐(+)‐rhamnose and (R, R)‐3‐(3‐hydroxydecanoyloxy) decanoic acid of rhamnolipid 1. The latter reaction occurred at a much lower rate. Direct addition of Naringinase to resting cells in an integrated microbial/enzymatic process was possible and resulted in an alteration of product composition from a rhamnolipid 1 and rhamnolipid 3 mixture to rhamnolipid 1 only.
Improvement of lipase stability in the presence of commercial triglycerides
Authors: Pirozzi Domenico 
Published: January 2004

AbstractSeveral compounds generated by atmospheric oxidation of triglycerides, such as hydroperoxides and secondary products, may cause significant lipase inactivation in low‐water medium. Activity decay is usually time‐dependent and shows a non‐linear dependence on inactivating compound concentration.As the effect of very dilute poisons becomes much more significant in continuous operations, stability tests were performed in the presence of oxidized oils in batch and continuous reactors. Experimental results show that the stability of Novozyme 435 is affected by secondary products of oxidation more than by hydroperoxides.Involvement of sulphydryl groups in the mechanism of lipase interaction with two aldehydes, 4‐hydroxynonenal (4‐HNE) and malondialdehyde (MDA), has been demonstrated by blocking the lipase sulphydryl groups with pHMB pre‐treatment. The preliminary neutralization 4‐HNE and MDA with albumin also increased enzyme stability.
Lipase‐catalyzed synthesis of designer acylglycerols rich in residues of eicosapentaenoic, docosahexaenoic, conjugated linoleic, and/or stearic acids
Authors: Torres Carlos F. , Lin Betty , Moeljadi Marlina , Hill, Jr. Charles G. 
Published: January 2004

AbstractLipase‐catalyzed glycerolysis of a commercial acylglycerol (TG500), rich in eicosapentaenoic residues, and subsequent reaction of the product acylglycerols via esterification and/or transesterification reactions were investigated for the purpose of preparing acylglycerols enriched in particular fatty acid residues. An immobilized lipase from Candida antarctica (fraction B) was employed as biocatalyst for these reactions. The effects of enzyme loading, molar ratio of substrates, type of acyl donor, and use of a continuous purge stream of nitrogen were evaluated. The transesterification reactions were carried out using the ethyl esters of 3 different fatty acids, namely stearic, conjugated linoleic, and docosahexaenoic acids. Final yields of triacylglycerols of 75‐80% were obtained for the transesterification reactions with the 3 different types of fatty acid ethyl esters.
Thermomyces lanuginosus lipase catalyzed transesterification of sterols by methyl oleate
Authors: Weber Nikolaus , Weitkamp Petra , Mukherjee Kumar D. 
Published: January 2004

AbstractPlant steryl and stanyl esters are effective in lowering plasma cholesterol concentration by inhibiting the absorption of cholesterol from small intestine. They are, therefore, used as constituents of special margarines, which are commercially available as functional foods with the ability to reduce blood cholesterol levels. An enzymatic method has been developed for the preparation of oleic acid esters of sterols and stanols in high yield by transesterification of methyl oleate with the 3‐hydroxy group in vacuo (20‐40 hPa) at moderate temperature (80 °C) using immobilized lipase preparation from Thermomyces lanuginosus (Lipozyme TL IM®) as biocatalyst. Neither an organic solvent nor a drying agent are required. Cholesterol and stanols such as 5α‐cholestanol and sitostanol have been converted at similar rates and in near‐quantitative yields (>95%) to the corresponding oleic acid esters.
Enzymatic fatty acid exchange in glycero‐phospholipids
Authors: Adlercreutz Patrick , Lyberg Ann‐Marie , Adlercreutz Dietlind 
Published: January 2004

AbstractLipases can be used to exchange fatty acids in the sn‐1 position of glycerophospholipids and phospholipase A2 is useful for the corresponding exchange reaction in the sn‐2 position. In both cases, the exchange can be done in a one‐step acidolysis process or in a two‐step process. In the latter case, the original fatty acid in the desired position is removed by enzymatic hydrolysis or alcoholysis and after isolation of the resulting lysophospholipid, the new fatty acid is introduced, using the same enzyme, in an esterification reaction. Several synthesis examples from the literature are reviewed. Incorporation of a new fatty acid into the sn‐1 position is more favourable than incorporation into the sn‐2 position because of the magnitudes of the equilibrium constants of the reactions and because lipases can be used at much lower water activity than phospholipase A2. With the consecutive use of both enzymes highly pure products with defined fatty acids in both positions can be obtained.
In vitro and in vivo biosynthesis of wax diesters by an unspecific bifunctional wax ester synthase/acyl‐CoA:diacylglycerol acyltransferase from Acinetobacter calcoaceticus ADP1
Authors: Kalscheuer Rainer , Uthoff Stefan , Luftmann Heinrich , Steinbüchel Alexander 
Published: January 2004

AbstractAcinetobacter calcoaceticus ADP1 possesses a bifunctional wax ester synthase/acyl‐CoA:diacylglycerol acyltransferase (WS/DGAT) catalyzing the biosynthesis of wax esters and triacylglycerols. The unspecificity of WS/DGAT was used for in vitro and in vivo biosynthesis of wax diesters consisting of 1, 16‐hexadecanediol esterified with longchain fatty acids. An in vitro assay employing the membrane fraction of recombinant Escherichia coli XL1‐Blue expressing wax/dgat coding for WS/DGAT and using 1, 16‐hexadecanediol and 1‐14 C‐palmitoyl‐CoA as substrates resulted in the production of 2 radiolabeled substances as revealed by autoradiography suggesting the acylation of one or both hydroxy groups of 1, 16‐hexadecanediol by WS/DGAT. For in vivo biosynthesis of wax diesters, the knock‐out mutant A. calcoaceticus ADP1acr1 | Km was generated by disruption of acr1 coding for acyl‐CoA reductase which caused the inability to synthesize fatty alcohols and, thus in consequence, wax esters. Co‐cultivation of A. calcoaceticus ADP1acr1 | Km on gluconate and 1, 16‐hexadecanediol in nitrogen‐limited mineral salts medium resulted in the accumulation of a mixture of wax diesters of 1, 16‐hexadecanediol esterified with palmitic and oleic acid as revealed by electron impact ionization mass spectrometry. 1‐Monopalmitoylglycerol could also be utilized as an alternative acyl acceptor by the unspecific WS/DGAT in vitro resulting in the synthesis of 1, 2‐ and 1, 3‐dipalmitoylglycerol, whereas 1‐oleoylglycerol‐3‐phosphate (lysophosphatidic acid) was not accepted.
N‐[4‐(dicyanomethylazo)phenyl]‐2‐saccharin‐2‐ylacetamide in the synthesis of pyridazine and pyrimidine derivatives
Authors: Aly A. A. , Nassar S. A. 
Published: January 2004

AbstractN‐[4‐(Dicyanomethylazo)phenyl]‐2‐saccharin‐2‐ylacetamide (2) proved to be a convenient precursor for the synthesis of a variety of pyridazine and pyrimidine derivatives 4a,b,6, and 7. Also a series of substituted pyrimidines 10–16 were prepared from the reaction of N‐[4‐(2‐amino‐1‐cyano‐2‐substitutedvinylazo)phenyl]‐2‐(saccharin‐2‐yl)acetamide 9a,b with different reagents via initial addition to either the cyano or amino group, followed by cyclization. Some of the synthesized heterocycles were screened for their biological activity. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 15:2–8, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10194
Experimental and theoretical studies on some new pyrrol‐2,3‐diones formation
Authors: Yildirim Ismail , Kandemirli Fatma 
Published: January 2004

Abstract4‐Benzoyl‐5‐phenyl‐2,3‐furandione (1) reacts with asymmetric disubstituted urea derivatives like 1,1‐dimethylurea (2a) and 1,1‐diethylurea (2b) by the elimination of a H2O molecule to give the 4‐benzoyl‐1‐(N,N‐dialkylcarbamyl)‐5‐phenyl‐2,3‐pyrroldiones 3a and 3b. The structures of 3a,b were determined by the 13C NMR, 1H NMR, IR spectroscopic data and elemental analyses. The electronic structures of the reactants, their transition states, intermediate states, and final products of the reactions were investigated on the basis of AM1 and ab initio (DFT) methods. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 15:9–14, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10204
Heterobimetallic heterocyclic derivatives of indium(III)
Authors: Bansal Seema , Singh Yashpal , Singh Anirudh 
Published: January 2004

AbstractReactions of InCl3 with potassium salts of bifunctional tridentate (L1H2HOC6H4CH NCH2CHMeOH) and monofunctional bidentate (L2HHOC6H4CHN‐i‐Bu) Schiff bases in 1:1 and 1:2 molar ratio in benzene afford complexes In(L1)Cl and In(L2)2Cl, respectively. On reaction with potassium isopropoxymetallates KB(O‐i‐Pr)4, KAl(O‐i‐Pr)4, KTi(O‐i‐Pr)5, and KNb(O‐i‐Pr)6, they produce interes‐ ting heterobimetallic heterocyclic complexes. These are characterized by elemental (N, B, Al, Ti, and Nb) analyses, molecular weight measurements, and spectral [IR, NMR (1H, 13C, 11B, and 27Al)] studies. Probable structures are suggested for them. © 2003 Wiley Periodicals, Inc. 15:21–25, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10206
Cyclobutane‐substituted diacetamido sulfides and 2,5‐diacylthiophenes
Authors: Koparır Metin , Cansız Ahmet , Ahmedzade Misir , Çetin Ahmet 
Published: January 2004

AbstractA general and convenient route for the synthesis of 2,5‐di[1‐methyl‐1‐arylcyclobutane‐3‐yl]‐ thiophenes 4a–c and bis[1‐methyl‐1‐arylcyclobutane‐3‐yl]‐2‐(2‐oxyethtylamido)thiazole sulfides 7a–c is reported. The characterization of these compounds was obtained by elemental analyses, IR, 13C, and 1H NMR techniques. © 2003 Wiley Periodicals, Inc. 15:26–31, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/.hc10207