Showing papers on "Carboxylic acid published in 1991"

Carbonylation: Direct Synthesis of Carbonyl Compounds

Abstract: 1. Introduction.- 2. Reaction Mechanisms in Carbonylation Chemistry.- 3. Practical Aspects.- 4. Synthesis of Aldehydes.- 5. Synthesis of Ketones.- 6. Synthesis of Carboxylic Acids.- 7. Synthesis of Esters.- 8. Synthesis of Amides and Further Carboxylic Acid Derivatives.- 9. Synthesis of Lactones.- 10. Synthesis of Lactams and Related N-Heterocycles.- 11. Decarbonylation Reactions.- 12. Catalyst Preparations and Recovery of Precious Metals.- Appendixes.- 1. Suppliers of Transition Metal Catalysts and Reagents.- 2. Carbon Monoxide Suppliers.- 3. Gas Monitors.- 4. Suppliers of Autoclave Equipment.- References.

Recognition of a cell-surface oligosaccharide of pathogenic Salmonella by an antibody Fab fragment.

Abstract: The 2.05 angstrom (A) resolution crystal structure of a dodecasaccharide-Fab complex revealed an unusual carbohydrate recognition site, defined by aromatic amino acids and a structured water molecule, rather than the carboxylic acid and amide side chains and a structured water molecule, rather than the carboxylic acid and amide side chains that are features of transport and other carbohydrate binding proteins. A trisaccharide epitope of a branched bacterial lipopolysaccharide fills this hydrophobic pocket (8 A deep by 7 A wide) in an entropy-assisted association (association constant = 2.05 x 10(5) liters per mole, enthalpy = -20.5 +/- 1.7 kilojoules per mole, and temperature times entropy = +10.0 +/- 2.9 kilojoules per mole). The requirement for the complementarity of van der Waals surfaces and the requirements of saccharide-saccharide and protein-saccharide hydrogen-bonding networks determine the antigen conformation adopted in the bound state.

Process for producing homogeneous modified copolymers of ethylene/alpha-olefin carboxylic acids or esters

Abstract: A homogeneous, random interpolymer of ethylene and an alpha-olefinically unsaturated carboxylic acid or ester having melt indices from 0.1 to 300 grams/10 minutes, as determined by ASTM D-1238 (190 °C/2160 grams), is improved during its manufacture when made in a substantially constant environment in a stirred autoclave under substantially steady-state conditions of temperature, pressure, and flow rates, said temperature and pressure being sufficient to produce a single phase reaction, using a free-radical initiator, said improvement being obtained by the use of a minor amount of a telogenic modifier in the reaction mixture, the process being further characterized by the use of either, or both, of (a) a temperature which is lower than that which would be required without the presence of the telogen, or (b) a pressure which is higher than that which would be required without the presence of the modifier.

Complexation of nucleotide bases by molecular tweezers with active site carboxylic acids: effects of microenvironment

Abstract: In chloroform-d molecular tweezer 1 forms a 1:l complex (Job plot) with 9-propyladenine (4). Changes in the UV-visible absorption spectrum of 1 upon addition of 4 and the changes 1 and 4 induce in each other's IH NMR spectrum are consistent with those of a complex comprised of hydrogen bonds and a-stacking interactions. The microenvironment around the carboxylic acid group in 1 markedly alters its complexation behavior relative to a simple carboxylic acid such as butyric acid (Lancelot, G. J. Am. Chem. SOC. 1977, 99,7037-7042). The association constants for the 1-4 and butyric acid-5 complexes are 25000 M-' (298 K) and 160 M-' (303 K), respectively. Butyric acid prefers a type 1 hydrogen bonding pattern while 1 adopts a type 7 pattern. The nucleotide base selectivities follow the order G > C > A > U for butyric acid and A > G >> C > U for 1. The presence of protic solvents markedly decreases the strength of the complex between 1 and 4. Two analogues of 1 have also been studied, molecular tweezer 2 and 3. Both lack the dimethylamino substituent found in 1, while 3 has a spacer unit that is fully oxidized. The association constants for the 2-4 and 3-4 complexes are 14000 and 120000 M-I, respectively.

Convergent functional groups. X. Molecular recognition of neutral substrates

Abstract: Complexation de molecules pinces avec des derives de l'adenine et des nucleosides puriques et pyrimidiques

Reforming of ethanol-dehydrogenation to ethyl acetate and steam reforming to acetic acid over copper-based catalysts

Abstract: The title reactions, 2CH3CH2OH→CH3COOC2H5+2H2 and CH3CH2OH+H2O→CH3COOH+2H2, were carried out over copper-based catalysts (Cu, Cu/SiO2, Cu/ZrO2, Cu/Al2O3, Cu/MgO, and Cu/ZnO). The selectivities to ethyl acetate and acetic acid markedly depended upon the supports used. Acetaldehyde was formed by the dehydrogenation of ethanol and transformed to either ethyl acetate or acetic acid through steps in which a nucleophilic addition of ethanol (or ethoxide ions) or water (or hydroxide ions) to acetaldehyde occurred. The rates of the transformation steps to ethyl acetate and acetic acid were appreciably affected by the kinds of supports used. The transformation steps proceeded slowly, compared with the dehydrogenation step.

Fluorescent fatty acids derived from dipyrrometheneboron difluoride dyes

Abstract: This invention relates to improved fluorescent fatty acid analogs derived from dipyrrometheneboron difluoride ("BDY") dyes that absorb light at wavelengths longer than 480 nm. The BDY fluorophore or a derivative thereof is incorporated at various locations along the alkyl portion of the fatty acid ("BDY fatty acid"). The general formula of a BDY fatty acid is as follows: ##STR1## wherein at least one of the substituents R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 is a carboxylic acid terminated alkyl residue containing 5 to 22 carbon atoms. The remaining substituents, singly or in any combination, are: additional alkyl or arylalkyl residues containing 1 to 16 aliphatic carbon atoms, or aryl or heteroaryl residues, or hydrogen. Symmetrically substituted BDY fluorophores are conveniently synthesized from a single pyrrole precursor in a "one-pot" reaction. Alternatively, BDY fatty acids are synthesized from two different pyrrole precursors. The combination of fatty acids with these electrically neutral, photostable, strongly colored, and mostly highly fluorescent BDY dyes having relatively narrow absorption and emission spectra results in an improved fluorescent probe particularly useful for studying natural and synthetic lipid membranes and related areas.

Transport of monocarboxylic acids at the blood-brain barrier: studies with monolayers of primary cultured bovine brain capillary endothelial cells.

Abstract: The kinetics and mechanism of the transport of monocarboxylic acids (MCAs) were studied by using primary cultured bovine brain capillary endothelial cells. Concentration-dependent uptake of acetic acid was observed, and the kinetic parameters were estimated as follows: the Michaelis constant, Kt, was 3.41 +/- 1.87 mM, the maximum uptake rate, Jmax, was 144.7 +/- 55.7 nmol/mg of protein/min and the nonsaturable first-order rate constant, Kd, was 6.66 +/- 1.98 microliters/mg of protein/min. At medium pH below 7.0, the uptake rate of [3H]acetic acid increased markedly with decreasing medium pH, whereas pH-independent uptake was observed in the presence of 10 mM acetic acid. An energy requirement for [3H]acetic acid uptake was also demonstrated, because metabolic inhibitors (2,4-dinitrophenol and rotenone) reduced significantly the uptake rate (P less than .05). Carbonylcyanide-p-trifluoro-methoxyphenylhydrazone, a protonophore, inhibited significantly the uptake of [3H]acetic acid at medium pH of 5.0 and 6.0, whereas 4,4'-diisothiocyanostilben-2,2'-disulfonic acid did not. Several MCAs inhibited significantly the uptake rate of [3H]acetic acid, whereas di- and tricarboxylic acids did not. The uptake of [3H]acetic acid was competitively inhibited by salicylic acid, with an inhibition constant, Ki, of 3.60 mM, suggesting a common transport system between acetic acid and salicylic acid. Moreover, at the medium pH of 7.4, salicylic acid and valproic acid inhibited significantly the uptake of [3H]acetic acid, demonstrating that the transport of MCA drugs could also be ascribed to the MCA transport system at the physiologic pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and structure of molecular tweezers containing active site functionality

Abstract: A series of molecules has been synthetized in which a functional group is buried inside an aromatic binding cleft. These novel compounds, called «molecular tweezers», have a methyl ester, a carboxylic acid or a nitrile in their clefts

4-(Tetrazolylalkyl)piperidine-2-carboxylic acids. Potent and selective N-methyl-D-aspartic acid receptor antagonists with a short duration of action.

Abstract: We have prepared a series of cis-4-(tetrazolylakyl)piperidine-2-carboxylic acids as potent and selective N-methyl-D-aspartic acid (NMDA) receptor antagonists. NMDA antagonists may prove to be useful therapeutic agents, for instance, as anticonvulsants, in the treatment of neurodegenerative disorders such as Alzheimer's disease and in the prevention of neuronal damage that occurs during cerebral ischemia. The compounds prepared were evaluated in vitro in both receptor binding assays [( 3H]CGS-19755, [3H]AMPA, and [3H]kainic acid) and in a cortical-wedge preparation (versus NMDA, quisqualic acid, and kainic acid) to determine affinity, potency, and selectivity. The new amino acids were also evaluated in vivo for their ability to block NMDA-induced convulsions in neonatal rats and NMDA-induced lethality in mice. The most potent compound of this series, 15 (LY233053), selectively displaced [3H]CGS-19755 binding with an IC50 of 107 +/- 7 nM and selectively antagonized responses due to NMDA in a cortical-wedge preparation with an IC50 of 4.2 +/- 0.4 microM. Compound 15 blocked both NMDA-induced convulsions in neonatal rats (minimum effective dose (MED) = 20 mg/kg ip) and NMDA-induced lethality in mice (MED = 5 mg/kg ip). This is the first example of an NMDA receptor antagonist that incorporates a tetrazole moiety as an omega-acid bioisostere. These amino acid antagonists are also unique from their phosphonic acid counterparts in that they have a shorter duration of action in vivo. For the treatment of acute disorders such as stroke, where an NMDA antagonist would be administered parenterally, the shorter duration of action may be beneficial, e.g., allowing for better dosage control. The combination of potent NMDA receptor antagonism and a short duration of action may make these compounds useful therapeutic agents in the treatment of a variety of neurological disorders.

Sorption of carboxylic acid from carboxylic salt solutions at PHS close to or above the pKa of the acid, with regeneration with an aqueous solution of ammonia or low-molecular-weight alkylamine

Abstract: Carboxylic acids are sorbed from aqueous feedstocks at pHs close to or above the acids' pH a into a strongly basic organic liquid phase or onto a basic solid adsorbent or moderately basic ion exchange resin. the acids are freed from the sorbent phase by treating it with aqueous alkylamine or ammonia thus forming an alkylammonium or ammonium carobxylate which dewatered and decomposed to the desired carboxylic acid and the alkylamine or ammonia.

Chiral synthesis via organoboranes. 30. Facile synthesis, by the Matteson asymmetric homologation procedure, of .alpha.-methyl boronic acids not available from asymmetric hydroboration and their conversion into the corresponding aldehydes, ketones, carboxylic acids, and amines of high enantiomeric purity

Abstract: 2-(α-Methylalkyl)- or 2-(α-arylethyl)-1,3,2-dioxaborinanes, RMeHC*BO 2 (CH 2 ) 3 (R=alkyl or aryl), of very high enantiomeric purity, not available from asymmetric hydroboration, can be prepared by the Matteson asymmetric homologation procedure of optically pure pinanediol or 2,3-butanediol boronate esters with (di-chloromethyl)lithium, LiCHCl 2 , conveniently generated in situ in THF at −78°C, followed by reaction with either a Grignard reagent or an alkyllithium, with subsequent removal of the chiral auxiliaries. α-Methyl boronic esters thus obtained are readily converted into the corresponding aldehydes by the reaction with [methoxy(phenylthio)methyl]lithium [LiCH(OMe)SPh] (MPML) and mercuric chloride, followed by oxidation with hydrogen peroxide in a pH 8 buffer medium. The two-phase aqueous chromic acid procedure can be used to oxidize these aldehydes to the corresponding α-methyl carboxylic acids of very high enantiomeric purity without significant racemization

Analysis of condensates from wood smoke : components derived from polysaccharides and lignins

Abstract: A feasibility study has been carried out of the analysis of total condensate (at {minus}50C) of smoke from smoldering combustion of wood. All of the phenol and furan components in the aqueous condensate were extracted into methylene chloride and the extract was analyzed by GC/MS. The same homologues of guaiacol and syringol derived from lignin were detected as have been described in earlier studies, but in addition, a series of furan derivatives were found. The latter are believed to arise from pyrolysis of polysaccharides. The carboxylic acids in the condensates were analyzed by titration and subsequent GC/MS. Acetic acid was the dominant volatile acid found, with a trace of propanoic, but no significant formic acid.

Novel catalytic enantioselective protonation (proton transfer) in Michael addition of benzenethiol to α-acrylacrylates: synthesis of (S)-naproxen and α-arylpropionic acids or esters

Abstract: A novel synthesis of optically active 2-phenylpropionic acids or esters via catalytic enantioselective protonation in the Michael addition of benzenethiol to 2-phenylacrylates is described; the synthetic utility is further demonstrated by the asymmetric synthesis of (S)-Naproxen.