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Selective Manner (selective + manner)
Selected AbstractsA Synthesis Detour to Planar-Diastereoisomeric Ferrocene Derivatives around an Unexpected Rearrangement of ortho -Lithiated Kagan's Template [S(S)] - (p -Tolylsulfinyl)ferroceneHELVETICA CHIMICA ACTA, Issue 4 2007Immo Weber Abstract Usually, ortho lithiation of Kagan's template 1 and quenching with electrophiles leads highly diastereoselectively to planar-chiral 1,2-disubstituted ferrocenes. Surprisingly, lithiation of 1 with lithium diisopropylamide (LDA) followed by addition of paraformaldehyde afforded regioisomer (+)-{[S(S)] - [4-(2-hydroxyethyl)phenyl]sulfinyl}ferrocene (2), which was converted to (+)-{[S(S)] - {4-{2-[(methylsulfonyl)oxy]ethyl}phenyl}sulfinyl}ferrocene (3) (Scheme,1). The desired diastereoisomer (l)-1-(hydroxymethyl)-2-(p -tolylsulfinyl)ferrocene (5) in turn could also be obtained by ortho lithiation of 1 with LDA but by quenching with DMF to yield aldehyde 4 first, which then was reduced with NaBH4 to 5. Finally, target compound (l)-1-[(dimethylamino)methyl]-2-(p -tolylsulfinyl)ferrocene (6) was obtained by substitution of the OH group of 5 under mild conditions or directly by ortho lithiation of 1 with lithio-2,4,6-triisopropylbenzene (=2,4,6-triisopropylphenyl)lithium; LTP) followed by quenching with N,N -dimethylmethyleneiminium chloride. At low temperatures, reaction of 1 with LDA leads, via the preferred diastereoisomeric transition state ,exo'- 7 and under extrusion of a (diisopropylamine)lithium complex of type 8, in a highly selective manner, to diastereoisomeric ortho -lithiated chelate (l)- 9 (Scheme,2). The reaction of 1 to 2 is explained by a rearrangement of (l)- 9 to {[S(S)],[4-(lithiomethyl)phenyl]sulfinyl}ferrocene 10, which is acid-catalyzed by coordinated diisopropylamine in complexes of type 8. This rearrangement is not observed if LTP is used as base or, in case LDA is applied, if the electrophile is sufficiently reactive at low temperatures. [source] Selective Preparation of Diamondoid Fluorides[1]ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Hartmut Schwertfeger Abstract The selective fluorination of diamantane, triamantane, [121]tetramantane, and [1(2,3)4]pentamantane bromides and alcohols was achieved by using the fluorinating agents silver fluoride (AgF) and diethylaminosulfur trifluoride (DAST). Various mono-, di-, tri- and even tetrafluorinated diamondoid derivatives were prepared and characterized. We were also able to prepare the amino fluoro and the fluoro alcohol derivatives of diamantane from the corresponding monoprotected diamondoid diols. These reactions can be carried out in a highly selective manner and proceed without isomerizations. The fluorinated, unequally disubstituted derivatives are valuable compounds for the exploration of electronic, pharmacological, and material properties of functionalized diamondoids. [source] Chemoenzymatic Route to Both Enantiomers of a 1-Isopropyl-3a-methyloctahydroinden-4-one Derivative: A Synthetic Intermediate for Sesqui- and DiterpenoidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2005Shigeo Fujieda Abstract On the way to a chemoenzymatic synthesis of a key intermediate for sesquiterpenoids and diterpenoids, 2-methyl-2-(4-methyl-3-oxopentyl)-1,3-cyclohexanedione was reduced with the whole cells of yeast biocatalysts. Torulaspora delbrueckii NBRC10921 reduced a cyclic ketone of three carbonyl groups in an enantiofacially selective manner (re -face attack), but there was poor enantiotopic group selectivity between two carbonyl groups on the cyclohexane ring to yield a mixture of diastereomeric products. Candida floricola IAM13115 reduced mainly the pro -(R) carbonyl group. In contrast, the reduction proceeded in an enantiofacially poorly selective manner to give another set of diastereomeric products. In both cases, another carbonyl group on the side chain worked as a ,trapping arm' of the resulting secondary alcohol. The diastereomeric products were effectively separated as the ,syn' or ,cis' isomer exclusively exist in the intramolecular hemiacetal structure, while ,anti' or ,trans' isomer being an equilibrated mixture of cyclic hemiacetal and open-chain hydroxyketone (ca. 0.7,:,1). Starting separately from the enantiomerically enriched products as above, both enantiomers of the target compound, a key intermediate for terpenoids, were efficiently prepared via stereoselective ring closure under pinacol coupling reaction conditions. Furthermore, a daucane sesquiterpene intermediate, a hydroazulene derivative, was provided after one-carbon homologation of the six-membered ring. [source] Combined tissue factor pathway inhibitor and thrombomodulin deficiency produces an augmented hypercoagulable state with tissue-specific fibrin depositionJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 1 2008S. A. MARONEY Summary.,Background and Objective:,Tissue factor pathway inhibitor (TFPI) and thrombomodulin (TM) are endothelial-associated anticoagulant proteins thought to control hemostasis in specific vascular beds. Here, we have examined the consequences of TFPI deficiency in the presence of a compounding procoagulant state caused by reduced TM function. Methods and results:,TFPI+/,/TMpro/pro mice are born at less than expected frequency in either TFPI+/,/TMpro/+ or TMpro/pro mothers but are born at near the expected frequency in TMpro/+ mothers. Adult TFPI+/,/TMpro/pro mice have elevated thrombin,antithrombin complex and increased thrombus volume in an electrical injury model of venous thrombosis. In striking contrast to mice with single deficiency of TFPI or TM, TFPI+/,/TMpro/pro mice exhibit augmented fibrin deposition not only in the liver, but also in the cerebral microvasculature. Conclusions:,TFPI+/,/TMpro/pro mice exhibit partial intrauterine lethality when carried by mothers with an underlying prothrombotic state, providing the first experimental evidence in an animal model that TFPI-dependent control of hemostasis in the vascular bed of the placenta fulfills a critical role for successful pregnancy outcome. In addition to the placenta, partial TFPI deficiency interacts with decreased TM function in an organ selective manner to produce fibrin deposition in other specific vascular beds, the liver and brain. [source] The production of route directions: investigating conditions that favour conciseness in spatial discourseAPPLIED COGNITIVE PSYCHOLOGY, Issue 1 2004Marie-Paule Daniel The study reported here investigated the effects of conditions expected to favour conciseness in the production of route directions. In Experiment 1, two groups of undergraduates were invited to give written descriptions of the route connecting two well-known places on their university campus. The control group received standard instructions, and the other group was instructed to produce route directions that were as concise as possible, while remaining sufficiently informative to guide a pedestrian to the goal. Not surprisingly, instructions to be concise resulted in an overall shortening of descriptions, but this occurred in a selective manner. In particular, actions and action-landmark combinations were the least affected, whereas the number of landmarks mentioned without being associated with actions, as well as of details describing landmarks, was considerably reduced. Furthermore, landmarks situated at points on the route involving a decision about changing direction underwent less reduction than other landmarks. In Experiment 2, conditions were created where conciseness was brought into play without any explicit instructions to be concise. Undergraduates were asked to work in groups of three, and each group was assigned the task of producing a single description. The results showed that the descriptions produced by a group were shorter than those produced by individuals. This was interpreted as reflecting that in the absence of any conciseness instructions, the feedback developed within groups during the production of route directions led to effective selection of the information content. Interestingly, the items relating actions and landmarks were almost fully preserved in the group descriptions. In Experiment 3, conciseness was shown to be further increased by combining instructions for conciseness and group production. Altogether, the three experiments revealed the primary role of propositions linking action prescriptions and landmarks at points on the route where key actions have to be taken. Copyright © 2003 John Wiley & Sons, Ltd. [source] Swelling Induced Detachment of Chondrocytes Using RGD-Modified Poly(N -isopropylacrylamide) Hydrogel BeadsBIOTECHNOLOGY PROGRESS, Issue 3 2002Mee Ryang Kim Thermally sensitive poly( N -isopropylacrylamide, NIPAAm) hydrogel beads conjugated with a cell adhesive motif, GRGDY, were prepared and utilized as cell culture substrate for chondrocytes. They were produced to be uniform in size and distribution by using calcium alginate as a temporal mold. The RGD moieties were introduced, in a spatially selective manner, to the surface of the beads by conjugating GRGDY under the precollapsed state at a higher temperature above the lower critical solution temperature (LCST). These RGD-conjugated polyNIPAAm beads demonstrated a reversible swelling and deswelling behavior around the LCST, which enabled the chondrocytes attached on the surface of collapsed beads at 37 °C to readily detach when the temperature was shifted below 37 °C. The cell detachment percentage was largely affected by the temperature-dependent reswelling extent of the collapsed RGD-modified beads. [source] Multivalent Binding of Small Guest Molecules and Proteins to Molecular Printboards inside MicrochannelsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2008Manon Abstract ,-Cyclodextrin (,-CD) monolayers have been immobilized in microchannels. The host,guest interactions on the ,-CD monolayers inside the channels were comparable to the interactions on ,-CD monolayers on planar surfaces, and a divalent fluorescent guest attached with a comparable binding strength. Proteins were attached to these monolayers inside microchannels in a selective manner by employing a strategy that uses streptavidin and orthogonal linker molecules. The design of the chip, which involved a large channel that splits into four smaller channels, allowed the channels to be addressed separately and led to the selective immobilization of antibodies. Experiments with labeled antibodies showed the selective immobilization of these antibodies in the separate channels. [source] Selective Guest Encapsulation by a Cobalt-Assembled Cage MoleculeCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005Roger G. Harrison Prof. Abstract Metal-assembled resorcinarene-based cages enclose space and entrap organic molecules from water. Addition of cobalt(II) ions to a neutral, aqueous solution of a resorcinarene that has iminodiacetic acids attached to its upper rim results in the formation of cages. These cages not only entrap organic molecules, but they do so in a selective manner. Guests with optimum size, shape, and polarity are preferentially entrapped. For example, selection of p -xylene is twenty thousand times more favorable than that of m -xylene. The enthalpy of resorcinarene deprotonation and cage formation was calculated by performing calorimetry studies and ranged from ,305 to ,348 kJ,mol,1. The change in enthalpy of guest encapsulation varied by as much as 43 kJ,mol,1. The differences in change in free energy of guest encapsulation varied by ,16 kJ,mol,1. The changes in enthalpy and free energy of guest encapsulation were used to calculate the changes in entropy, which ranged from ,97 to +37 J,mol,1,K,1. An enthalpy,entropy compensation of guest encapsulation was observed. [source] Nickel-Catalyzed Mizoroki,Heck- versus Michael-Type Addition of Organoboronic Acids to ,,,-Unsaturated Alkenes through Fine-Tuning of LigandsCHEMISTRY - AN ASIAN JOURNAL, Issue 11 2007Pao-Shun Lin Abstract Various arylboronic acids reacted with activated alkenes in the presence of [Ni(dppe)Br2], ZnCl2, and H2O in CH3CN at 80,°C to give the corresponding Mizoroki,Heck-type addition products in good to excellent yields. Furthermore, 1,equivalent of the hydrogenation product of the activated alkene was also produced. By tuning the ligands of the nickel complexes and the reaction conditions, Michael-type addition was achieved in a very selective manner. Thus, various p- and o- substituted arylboronic acids or alkenylboronic acid reacted smoothly with activated alkenes in CH3CN at 80,°C for 12,h catalyzed by Ni(acac)2, P(o -anisyl)3, and K2CO3 to give the corresponding Michael-type addition products in excellent yields. However, for m- substituted arylboronic acids, the yields of Michael-type addition products are very low. The cause of this unusual meta -substitution effect is not clear. By altering the solvent or phosphine ligand, the product yields for m- substituted arylboronic acids were greatly improved. In contrast to previous results in the literature, the present catalytic reactions required water for Mizoroki,Heck-type products and dry reaction conditions for Michael-type addition products. Possible mechanistic pathways for both addition reactions are proposed. [source] | ||||||||||