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PubMed2004

Reactivity of (bicyclo[5.1.0]octadienyl)iron(1+) cations: application to the synthesis of cis-2-(2'-carboxycyclopropyl)glycines.

The addition of carbon and heteroatom nucleophiles to (bicyclo[5.1.0]octadienyl)Fe(CO)(2)L(+) cations 5 or 8 (L = CO, PPh(3)) generally proceeds via attack at the dienyl terminus on the face of the ligand opposite to iron to generate 6-substituted (bicyclo[5.1.0]octa-2,4-diene)iron complexes (11 or 13). In certain cases, these products are unstable with respect to elimination of a proton and the nucleophilic substituent to afford (cyclooctatetraene)Fe(CO)(2)L (4 or 7). Decomplexation of 13f, arising from addition of phthalimide to 8, gave N-(bicyclo[5.1.0]octa-3,5-dien-2-yl)phthalimide (19). Oxidative cleavage of 19 (RuCl(3)/NaIO(4)) followed by esterification gave the cyclopropane diester 22, which upon hydrolysis gave cis-2-(2'-carboxycyclopropyl)glycine (CCG-III, 18) (eight steps from 4, 43% overall yield). This methodology was also utilized for preparation of stereospecifically deuterated CCG-III (d-18) and optically enriched (-)-18. Deprotonation of 22 resulted in cyclopropane ring opening to afford the benzoindolizidine (23).

Bridged Bicyclo Compounds↗
PubMed1976

[Reactivation of phosphorylated acetylcholinesterase (AChE): quaternary salts of vinylogous pyridinaldoxims (author's transl)].

Application of Wittig reaction to 4-pyridinecarboxaldehyde leads to 4-beta-formylvinylpyridine (62%). The corresponding oxime (4-(2)) can be quaternized with alpha,alpha'-bis-(chloromegonin), and with methyliodide one to 4-PAM (4-(3)). In this case the formal insertion of an ethylenic double bond between the pyridinium ring and the aldoxime group decreases the ability to reactivate phosphorylated acetylcholinesterase (AChE).

Acetylcholinesterase↗
PubMed2005

[Photovoltaic character of organic EL devices MEH-PPV/Alq3].

An organic photovoltaic(PV) cell, ITO/MEH-PPV/Alq3/LiF/Al, was fabricated. The MEH-PPV and Alq3 are the electron-acceptor and donor in the cell, respectively. The respond region matchs the adsorption of Alq3 film. Under UV light with 0.5 mW x cm(-2), the cell shows a short-circuit current of 2.4 microA x cm(-2), open-circuit voltage of 2.6 V, a fill factor of 0.71, and a power conversion efficiency of 0.9%. It was found that the PV cell indicates electroluminescence (EL) performance and could emit orange light at DC voltage. The maximum luminance is about 1 000 cd x cm(-2) at 15 V.

Aluminum↗
PubMed2004

1-alkoxyvinyl esters: renaissance of half-century-old acyl donors with potential applicability.

Among the various kinds of acyl donors, the 1-alkoxyvinyl esters have characteristic features, such as a high reactivity under nearly neutral conditions and the generation of neutral and volatile esters as single coproducts. Although their use in organic syntheses began in the middle of the 1950s, no significant progress has been seen. This is probably because the existing method of preparing alkoxyvinyl esters used toxic mercuric salts and was not totally applicable for those esters having functionalized acyl moieties. We have discovered that the use of a catalytic amount of the less toxic [RuCl2(p-cymene)]2 effectively accelerates the addition of carboxylic acids to ethoxyacetylene to give ethoxyvinyl esters bearing a variety of functionalized acyl groups in high yields. This discovery has opened a new avenue for developing new reactions and new synthetic methodologies based on the design and use of these acyl donors with suitable functional groups. Such examples include (i) the installation of hydrophilic acyl moieties on biologically active compounds, (ii) asymmetric Pummerer-type reactions, (iii) aromatic Pummerer-type reactions, (iv) the lipase-catalyzed desymmetrization of symmetrical 1,3-diols, and (v) lipase-catalyzed domino reactions. Future possibilities for these acyl donors are also discussed.

Catalysis↗
PubMed2003

Sevoflurane degradation by carbon dioxide absorbents may produce more than one nephrotoxic compound in rats.

PURPOSE: Degradation of sevoflurane by carbon dioxide absorbents produces compound A, a vinyl ether. In rats, compound A can produce renal corticomedullary necrosis. We tested whether other compounds produced by sevoflurane degradation also could produce corticomedullary necrosis. METHODS: Two groups of rats were exposed for four hours to sevoflurane 2.5% delivered through a container filled with fresh Sodasorb and heated to 30 degrees C or to 50 degrees C, respectively. Compound A was added to produce an average concentration of 120 ppm in both groups. A third (control) group received 2.5% sevoflurane that did not pass through absorbent, and no compound A was added. RESULTS: As determined by gas chromatography, the higher temperature produced more volatile breakdown products, including compound A. Median necrosis of the corticomedullary junction in the 50 degrees C group [10% (quartiles 1.0%-7.8%); n = 20] exceeded that in the 30 degrees C group [5% (6.5%-15%); n = 18; P < 0.02], and both exceeded the median necrosis in the control group [0% (0.0%-0.2%); n = 10; P < 0.02]. The respective mean +/- SD values for these three studies were: 12.8 +/- 16.7%, 5.3 +/- 4.4%, and 0.3 +/- 0.5%. CONCLUSION: Degradation products of sevoflurane other than compound A can cause or augment the renal injury in rats produced by compound A.

Absorption↗
PubMedDate not supplied

Sevoflurane degradation product concentrations with soda lime during prolonged anesthesia.

STUDY OBJECTIVES: To evaluate the decomposition of sevoflurane in soda lime during prolonged sevoflurane anesthesia in humans. To evaluate for evidence of renal or hepatotoxicity as a result of exposure to these sevoflurane degradation compounds. DESIGN: Prospective evaluation in healthy volunteers. SETTING: Clinical research unit and postanesthesia care unit of a university hospital. PATIENTS: Six healthy male volunteers. INTERVENTIONS: Subjects were anesthetized with sevoflurane 1 to 1.2 minimum alveolar concentration for greater than 9 hours with a semiclosed circuit anesthetic technique (5-liter total flow) with fresh soda lime as the absorbent. MEASUREMENTS AND MAIN RESULTS: Laboratory tests of renal and hepatic function were performed before anesthesia and 1 and 5 days after anesthesia. During sevoflurane anesthesia, inhalation and exhalation circuit limb gas samples were obtained for degradation compound analysis. Only one degradation product, fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether (compound A), was detected. Inhalation concentration was maximal (7.6 +/- 1.0 ppm) at 2 hours and did not increase further after this time point. There were no differences in preanesthesia and postanesthesia tests of hepatic and renal function. CONCLUSIONS: Levels of the degradation compound (compound A) produced in semiclosed circuit sevoflurane anesthesia with soda lime are well below potential toxic levels and thus appear safe. When sevoflurane is administered under these conditions for prolonged anesthesia, concentrations of compound A do not continue to increase throughout anesthesia.

Adsorption↗
PubMed2005

Investigations of step-growth thiol-ene polymerizations for novel dental restoratives.

OBJECTIVES: The goal of this work was to investigate the feasibility of formulating novel dental restorative materials that utilize a step-growth thiol-ene photopolymerization. Particularly, we are aiming to significantly reduce the polymerization shrinkage and shrinkage stress while retaining adequate physical properties as compared to current dimethacrylatre-based systems. METHODS: The thiol-ene system is composed of a 4:3 molar mixture of triallyl-1,3,5-triazine-2,4,6-trione (TATATO) and pentaerythritol tetramercaptopropionate (PETMP). The simultaneous measurement of shrinkage stress and functional group conversion was performed. Solvent extraction of unreacted monomers and dynamic mechanical analysis on the polymer networks that were formed were also studied. Flexural strength was measured for both filled and unfilled PETMP/TATATO and Bis-GMA/TEGDMA systems. RESULTS: Photopolymerization of PETMP/TATATO occurs at a much higher rate, with the maximum polymerization rate six times faster, than Bis-GMA/TEGDMA cured under the identical conditions. The results from the simultaneous measurement of shrinkage stress and conversion showed that the onset of shrinkage stress coincides with the delayed gel point conversion, which is predicted to be 41% for the 3:4 stoichiometric PETMP/TATATO resin composition. The maximum shrinkage stress developed for PETMP/TATATO was about 0.4 MPa, which was only approximately 14% of the maximum shrinkage stress of the Bis-GMA/TEGDMA system. Adequate flexural strength and flexural modulus values were obtained for both filled and unfilled PETMP/TATATO systems. SIGNIFICANCE: The dramatically reduced shrinkage stress, increased polymerization rate, significance increased functional group conversion, and decreased leachable species are all benefits for the use-of thiol-ene systems as potential dental restorative materials.

3-Mercaptopropionic Acid↗
PubMed2002

Towards alpha- or beta-D-C-glycosyl compounds by tin-catalyzed addition of glycosyl radicals to acrylonitrile and vinylphosphonate, and flexible reduction of tetra-O-acetyl-alpha-D-glucopyranosyl bromide with cyanoborohydride.

Photo-induced radical addition of acetylated alpha-D-glucopyranosyl bromide (1). to acrylonitrile or diethyl vinylphosphonate, in the presence of catalytic amounts of tri-n-butyltin chloride and sodium (or tetra-n-butylammonium) cyanoborohydride in excess, allowed efficient preparations of alpha-configurated nonononitrile and 2-(alpha-D-glucopyranosyl)-ethylphosphonate (79, 70% yields, respectively). These conditions led to 2-(alpha-D-manno-, and galactopyranosyl)-ethylphosphonates in 68 and 76% yields. Similarly, radical addition of acetylated 1-bromo-beta-D-glucopyranosyl chloride (2). to acrylonitrile or diethyl vinylphosphonate afforded mainly intermediate chlorides which, upon radical reduction with excess tri-n-butyltin hydride, afforded the corresponding beta anomers (40 and 38%, respectively) by sequential C-C and C-H bond formation. Stereocontrol relies on the alpha-stereoselective quenching of D-glycopyranos-1-yl radicals. We found also that UV light irradiation of 1 with excess NaBH(3)CN in tert-butanol afforded either 1,3,4,6-tetra-O-acetyl-2-deoxy-alpha-D-arabino-hexopyranose (65% after crystallization) or, when 10% mol thiophenol was added, 2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-glucitol (79%). These are simple, tin-free, and easily controlled conditions, which compare well with known preparations of these reduced sugars.

Acetylation↗
PubMed2000

Spectra and structure of silicon containing compounds. XXVII. Raman and infrared spectra, conformational stability, vibrational assignment and ab initio calculations of vinyldichlorosilane.

The infrared (3200-30 cm(-1) spectra of gaseous and solid and the Raman spectra of liquid (3200-30 cm(-1), with quantitative depolarization values, and solid vinyldichlorosilane, CH2=CHSiHCl2, have been recorded. Both the gauche and the cis conformers have been identified in the fluid phases. Variable temperature (105-150 degrees C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data the enthalpy difference has been determined to be 20 +/- 5 cm(-1) (235 +/- 59 J mol(-1) with the gauche conformer the more stable rotamer. It was not possible to obtain a single conformer in the solid even with repeated annealing of the sample. The experimental enthalpy difference is in agreement with the prediction from MP2/6-311 + G(2d,2p) ab initio calculations with full electron correlation. However, when smaller basis sets, i.e. 6-31G(d) and 6-311 + G(d,p) were utilized the cis conformer was predicted to be the more stable form. Complete vibrational assignments are proposed for both conformers based on infrared contours, relative infrared and Raman intensities, depolarization values and group frequencies, which are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations. From the frequencies of the Si-H stretches, the Si-H bond distance of 1.474 A has been determined for both the gauche and the cis conformers. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G(d), 6-311 + G(d,p) and 6-311 + (2d,2p) basis sets at level of Hartree-Fock (RHF) and/or Moller Plesset to the second order (MP2) with full electron correlation. The potential energy terms for the conformer interconversion have been obtained from the MP2/6-31G(d) calculations. The results are discussed and compared with those obtained for some similar molecules.

Molecular Conformation↗
PubMed2003

Hydrogen bond directed highly regioselective palladium-catalyzed allylic substitution.

The palladium-catalyzed allylic substitution of 5-vinyloxazolidinones and derivatives was investigated. Unusual and high regioselectivity for the branched product was observed. The regioselectivity was influenced by the type of substrate, the solvents, and the nucleophile. Imide-type nucleophiles were found to be directed to the internal carbon (branched:linear, 75:25 to >98:2), whereas sulfonamides, amines, and malonates added only to the terminal carbon of the allyl complex. Relatively nonpolar solvents such as toluene and THF favored the branched product (97:3 and 95:5, respectively). Acetonitrile and dichloromethane afforded lower regioselectivity (50:50 and 67:33, respectively), and the use of the protic solvent ethanol resulted in reversal of the regioselectivity (12:88). The directing group on the substrate was important. Amides afforded almost complete formation of the branched product, and carbamates gave a 50:50 mixture of regioisomers with phthalimide as the nucleophile. Evidence for direction of the nucleophile via hydrogen bonding was obtained by replacing the hydrogen of the amide with a methyl, resulting in the production of only the normal linear product.

Allyl Compounds↗