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At least 469 records · Page 26Linked to original sources
PubMed2003

Analysis of a model reaction system containing cysteine and (E)-2-methyl-2-butenal, (E)-2-hexenal, or mesityl oxide.

Cysteine conjugates, resulting from the addition of cysteine to alpha,beta-unsaturated carbonyl compounds, are important precursors of odorant sulfur compounds in food flavors. The aim of this work was to better understand this chemistry in the light of the unexpected double addition of cysteine to two unsaturated aldehydes. These reactions were studied as a function of pH. When (E)-2-methyl-2-butenal (tiglic aldehyde, 4) was treated with cysteine in water at pH 8, the major product formed was the new compound (4R)-2-(2-[[(2R)-2-amino-2-carboxyethyl]thio]methylpropyl)-1,3-thiazolidine-4-carboxylic acid (6). Under acidic conditions (pH 1), we also observed a double addition, but the second cysteine was linked by a vinylic sulfide bond to form the previously unreported major product, (2R,2'R,E)-S,S'-(2,3-dimethyl-1-propene-1,3-diyl)bis-cysteine (7). When (E)-2-hexenal (12) was treated with cysteine under acidic conditions, the major product was the novel (4R,2' 'R)-2-[2'-(2' '-amino-2' '-carboxyethylthio)pentyl]-1,3-thiazolidine-4-carboxylic acid (13), and the formation of an vinylic sulfide compound analogous to 7 was not observed. Reduction of the acidic crude reaction mixture with NaBH(4) afforded 13 and the cysteine derivative (R)-S-[1-(2-hydroxyethyl)butyl]cysteine (14) in 14% yield. Treating (E)-2-hexenal with cysteine at pH 8 followed by NaBH(4) reduction yielded the new product (3R)-7-propylhexahydro-1,4-thiazepine-3-carboxylic acid (15). Addition of cysteine to mesityl oxide (16), at pH 8, followed by reduction with NaBH(4) furnished (R)-S-(3-hydroxy-1,1-dimethylbutyl)cysteine (3) and the new compound (3R)-hexahydro-5,7,7-trimethyl-1,4-thiazepine-3-carboxylic acid (18).

Aldehydes↗
PubMed2001

Physiologically based clearance/extraction models for compounds metabolized in the nose: an example with methyl methacrylate.

Airstream clearance (with units of volume/time) is the volumetric flow from which chemical would have to be completely removed to account for the net loss in the nose. Extraction is the proportion of airflow from which the chemical is completely removed. Over the past several years we have developed physiologically based clearance-extraction (PBCE) models for the nose to assess the physiological, biochemical, and anatomical factors that control airstream clearance. A generic clearance equation was derived for single airway/tissue compartments that had a separate air region and either one, two, or three underlying tissue regions. For all of these structures, airstream clearance (Cl(sys)) has a common form-Equation (1)-related to tissue clearance (Cltot), gas-phase diffusional clearance (PAgas), airflow (Q), and the mucus air partition coefficient (Hmuc:a). Clsys = CltotHm:aPAgasQ/CltotHm:a(Q + PAgas) + PAgasQ. A physiologically based clearance-extraction (PBCE) model for the whole nose combined three separate nasal tissue regions, each with a four-compartment tissue stack (air, mucus, epithelial tissue, and submucosal region). A steady-state solution of the PBCE model successfully described literature results on the steady-state extraction of methyl methacrylate (MMA) and several other metabolized vapors. Model-derived tissue dosimetry estimates, that is, the amount of MMA metabolized in the target epithelial compartment of the olfactory region, for rats and humans provide dosimetric adjustment factors (DAFs) required in calculating a human reference concentration (RfC) from rodent studies. Depending on the assignment of esterase activities to sustentacular and submucosal regions, the DAFs from the PBCE model varied between 1.6 and 8.0, compared to the default value of 0.145. From the experience with MMA, a minimal data set could be defined for building the PBCE model. It consists of mucus:air and blood:air partition coefficients, metabolic constants for enzymatic hydrolysis in nasal tissues from rat and human tissues, immunohistochemistry of the distribution of these activities in rats and human olfactory tissues, and extraction studies in anesthetized rats to assess the total nasal metabolism of the test compound.

Algorithms↗
PubMed1995

Nephrotoxicity in rats undergoing a one-hour exposure to compound A.

We previously demonstrated that rats experienced renal injury when exposed for 3-12 h to 50 ppm or more of a vinyl ether called Compound A [CF2 = C(CF3)OCH2F], a compound produced by CO2 absorbents acting on sevoflurane. These durations of exposure exceed the average duration of clinical anesthesia. We now report the effect of a 1-h exposure to 0, 100, 150, 200, 400, 600, or 800 ppm of Compound A in oxygen in 145 Wistar rats. Twenty-four hours after exposure, we obtained kidney and liver specimens for microscopic examination, applying hematoxylin and eosin, and (separately) an immunochemical marker (PCNA) for cell proliferation (regeneration). Compared with results from control rats (those breathing oxygen for 1 h), renal injury (defined as necrosis of the outer strip of the outer medullary layer or "corticomedullary junction necrosis") occurred at and above 200 ppm. Exposure to 150 ppm produced cell regeneration (i.e., stimulated cell proliferation). We conclude that the threshold concentrations for nephrotoxicity (i.e., minimal toxicity) for a 1-h exposure to Compound A exceed the maximum concentrations (particularly those at low inflow rates) reported in clinical practice by a factor of 2-3. If these threshold effects in rats apply to humans, one 1-h exposure to sevoflurane probably would not alter usual measures of renal function.

Animals↗
PubMedDate not supplied

Comparative metabolism and disposition of 1-chloro- and 3-chloro-2-methylpropene in rats and mice.

A recent 2-year carcinogenicity study found that gavage administration of 3-chloro-2-methylpropene (CMP), containing 5% 1-chloro-2-methylpropene (dimethylvinyl chloride, DMVC), caused forestomach neoplasms in rats and mice. Similar chronic studies revealed that DMVC caused forestomach neoplasms in both rats and mice; neoplasms of the nasal and oral cavities were observed in rats but not in mice. In the current studies we have investigated the metabolic basis of these differences. Daily doses of 150 mg/kg of 2-[14C]DMVC or 2-[14C]CMP were administered to rats for 1, 2, or 4 consecutive days. One daily dose of 150 mg/kg of DMVC was administered to mice. Both DMVC and CMP were rapidly metabolized; however, CMP was cleared at a slightly lower rate. Rats exhaled approximately 25 and 10% of the DMVC and CMP as CO2, respectively. Mice exhaled 25% of the DMVC as CO2. Rats expired 30% of the administered DMVC unchanged in the 24 hr after dosing compared to only 7% of the administered CMP. Mice expired 5% of the administered DMVC in the same time period. This observation may explain the occurrence of tumors in the nasal and oral cavities of rats treated with DMVC but not in rats treated with CMP or in mice treated with DMVC in 2-year carcinogenicity studies. The 24-hr urinary excretion in rats was 35% of the administered DMVC compared to 58% of CMP. Mice excreted 47% of the administered DMVC in 24 hr in the urine. An unusual urinary metabolite of DMVC, 2-amino-6-methyl-4-thia-5-heptene-1,7-dioic acid, was identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylation↗
PubMed2004

Reactive coupling of 4-vinylaniline with hydrogen-terminated Si(100) surfaces for electroless metal and "synthetic metal" deposition.

Pristine and resist-patterned Si(100) substrates were etched by aqueous HF to produce hydrogen-terminated silicon (H-Si(100)) surfaces. The H-Si(100) surface was then subjected to UV-induced reactive coupling of 4-vinylaniline (VAn) to produce the VAn monolayer-modified silicon (VAn-Si) surface. The VAn-Si surface was first functionalized with a "synthetic metal" by oxidative graft polymerization of aniline with the aniline moieties of the coupled VAn molecules. The composition and topography of the VAn-Si and polyaniline (PAn)-grafted VAn-Si (PAn-VAn-Si) surfaces were characterized by X-ray photoelectron spectroscopy and atomic force microscopy, respectively. The doping-undoping (protonation-deprotonation) and redox-coupling (metal reduction) behavior, as well as the electrical conductivity, of the surface-grafted PAn were found to be similar to those of the aniline homopolymer. The VAn-Si surface was also funtionalized by the electroless plating of copper. Not only did the VAn layer provide chemisorption sites for the palladium catalyst, in the absence of prior sensitization by SnCl2, during the electroless plating process, it also served as an adhesion promotion layer and a low-temperature diffusion barrier for the electrolessly deposited copper. Finally, micropatterning of the grafted PAn and of the electrolessly deposited copper were demonstrated on the resist-patterned VAn-Si surfaces.

Aniline Compounds↗
PubMed2002

A general, highly enantioselective method for the synthesis of D and L alpha-amino acids and allylic amines.

Catalytic and enantioselective synthesis of amino acids is a subject of intense interest in the field of asymmetric catalysis. Traditionally, researchers have concentrated their efforts largely on the design and discovery of enantiopure catalysts for the Strecker reaction, alkylation of tert-butyl gylcinate-benzophenone, electrophilic amination of carbonyl compounds, and hydrogenation of N-acyl-aminoacrylic acid; however, the scope of these reactions is limited. In this paper, we report on a different approach to amino acids based on an expeditious route to enantiopure allylic amines. A highly enantioselective and catalytic vinylation of aldehydes leads to allylic alcohols that are then transformed to the allylic amines via Overman's [3,3]-sigmatropic rearrangement of imidates. Oxidative cleavage of the allylic amines furnishes the amino acids in good yields and excellent ee's. The scope and utility of this method are demonstrated by the synthesis of challenging allylic amines and their subsequent transformation to valuable nonproteinogenic amino acids, including both D and L configured (1-adamantyl)glycine.

Alcohols↗
PubMed1987

Synthesis and antifungal activity of new 1-vinylimidazoles.

Carbonyl compounds I were subjected to an imidazole transfer reaction with N,N'-sulfinyldiimidazole or N,N'-carbonyldiimidazole to obtain the diimidazole II and the monoimidazole III. Various 1-vinylimidazoles IV, derived from o-hydroxyacetophenones by imidazole transfer reaction, were alkylated to furnish the title compounds V. The structure-activity relationships of these 1-vinylimidazole compounds V are described.

Candida albicans↗
PubMed1965

THE MAGNESIUM-ION-DEPENDENT CLEAVAGE OF THE VINYL ETHER LINKAGE OF BRAIN ETHANOLAMINE PLASMALOGEN.

1. There was a significant decrease in the amount of endogenous ethanolamine phospholipids when preparations of whole brain were incubated in bicarbonate-Ringer solutions, leading in particular to the hydrolysis of vinyl ether groups. 2. The hydrolysis of ethanolamine phospholipids in such preparations was abolished in the absence of bivalent cations. 3. An enzyme present in extracts of acetone-dried brain powders that cleaved the vinyl ether linkage in ethanolamine plasmalogen maximally at pH 7.4 required Mg(2+) for activity. 4. The cleavage of the vinyl ether linkage of an ethanolamine lysoplasmalogen was enhanced in the presence of Mg(2+) but the requirement was not absolute.

Brain↗
PubMedDate not supplied

The Microsponge Delivery System (MDS): a topical delivery system with reduced irritancy incorporating multiple triggering mechanisms for the release of actives.

The Microsponge Delivery System (MDS) is a unique technology for the controlled release of topical agents and consists of macroporous beads, typically 10-25 microns in diameter, loaded with active agent. When applied to the skin, the MDS releases its active ingredient on a time mode and also in response to other stimuli (rubbing, temperature, pH, etc). MDS technology is being used currently in cosmetics, over-the-counter (OTC) skin care, sunscreens and prescription products. By delivering the active gradually to the skin, MDS-benzoyl peroxide formulations, for example, have excellent efficacy with minimal irritation. These are typical benefits from the use of the MDS.

Acne Vulgaris↗
PubMed2005

Synthesis of the 3-methylene-2-vinyltetrahydropyran unit; the hallmark of the sesquiterpene, hodgsonox.

[structure: see text] The synthesis of some simple compounds containing the previously unreported 3-methylene-2-vinyltetrahydropyran system, a unique feature of the liverwort metabolite, hodgsonox is reported. Key features are the creation of an acrolein substituted in the alpha-position with a three-carbon chain bearing a terminal electrophilic site, addition of a vinyl group, and cyclization.

Magnetic Resonance Spectroscopy↗