Chiral micellar electrokinetic chromatography-atmospheric pressure photoionization of benzoin derivatives using mixed molecular micelles. (17/26)

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Effects of Litchi chinensis fruit isolates on prostaglandin E(2) and nitric oxide production in J774 murine macrophage cells. (18/26)

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A continuum of progress: applications of N-hetereocyclic carbene catalysis in total synthesis. (19/26)

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Spectroscopic and electrochemical characterization of some Schiff base metal complexes containing benzoin moiety. (20/26)

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Microwave-assisted efficient synthesis of 2-hydroxydeoxybenzoins from the alkali degradation of readily prepared 3-aryl-4-hydroxycoumarins in water. (21/26)

This paper describes an operationally simple, green and efficient approach for the synthesis of 2-hydroxydeoxybenzoins bearing diverse substituents from the microwave-assisted alkali degradation of 3-aryl-4-hydroxycoumarins in water. The latter compounds were readily prepared from the intramolecular Claisen condensation reaction of methyl 2-(2-arylacetoxy)benzoates in the presence of Cs2CO3-acetone, in excellent yields and without laborious workup procedures. This method is highly atom-economic and thus applicable for the large-scale synthesis of 2-hydroxydeoxybenzoins.  (+info)

Benzaldehyde lyase, a novel thiamine PPi-requiring enzyme, from Pseudomonas fluorescens biovar I. (22/26)

Pseudomonas fluorescens biovar I can grow on benzoin as the sole carbon and energy source. This ability is due to benzaldehyde lyase, a new type of enzyme that irreversibly cleaves the acyloin linkage of benzoin, producing two molecules of benzaldehyde. Benzaldehyde lyase was purified 70-fold and found to require catalytic amounts of thiamine PPi (TPP) and a divalent cation as cofactors. Optimal activity was obtained with a 1.0 mM concentration of Mn2+, Mg2+, or Ca2+. Gel permeation chromatography indicated a native molecular weight of 80,000, whereas the enzyme migrated in sodium dodecyl sulfate-containing polyacrylamide gels as a single polypeptide with a molecular weight of 53,000. Benzaldehyde lyase is highly specific; of a variety of structurally related compounds tested, only benzoin and anisoin (4,4'-dimethoxybenzoin) acted as substrates, their apparent Kms being 9.0 x 10(-3) and 3.25 x 10(-2) mM, respectively. A catalytic mechanism for the enzyme is proposed.  (+info)

Mechanism of oxidative C alpha-C beta cleavage of a lignin model dimer by Phanerochaete chrysosporium ligninase. Stoichiometry and involvement of free radicals. (23/26)

The hemoprotein ligninase of Phanerochaete chrysosporium Burds. catalyzes the oxidative cleavage of lignin model dimers between C alpha and C beta of their propyl side chains. The model dimers hitherto used give multiple products and complex stoichiometries upon enzymatic oxidation. Here we present experiments with a new model dimer, 1-(3,4-dimethoxyphenyl)-2-phenylethanediol (dimethoxyhydrobenzoin, DMHB) which is quantitatively cleaved by ligninase in air to give benzaldehyde and veratraldehyde according to the stoichiometry: 2DMHB + O2----2PhCHO + 2Ph(OMe)2CHO. Catalytic amounts of H2O2 are required for this aerobic reaction. Under anaerobic conditions, ligninase uses H2O2 as the oxidant for cleavage: DMHB + H2O2----PhCHO + Ph(OMe)2CHO. Electron spin resonance experiments done in the presence of spin traps, 2-methyl-2-nitrosopropane or 5,5-dimethyl-1-pyrroline-N-oxide, show that C alpha-C beta cleavage yields alpha-hydroxybenzyl radicals as intermediate products. Under anaerobic conditions, these radicals react further to give the final aldehyde products. In air, O2 adds to the carbon-centered radicals, probably giving alpha-hydroxybenzylperoxyl radicals which fragment to yield superoxide, benzaldehyde, and veratraldehyde. These results lead us to propose a mechanism for C alpha-C beta cleavage in which attack by ligninase and H2O2 on the methoxylated ring of DMHB yields a cation radical, which then cleaves to give either benzaldehyde and an alpha-hydroxy(dimethoxybenzyl) radical or veratraldehyde and an alpha-hydroxybenzyl radical (cf. Kersten, P. J., Tien, M., Kalyanaraman, B., and Kirk, T.K. (1985) J. Biol. Chem. 260, 2609-2612; Snook, M. E., and Hamilton, G. A. (1974) J. Am. Chem. Soc. 96, 860-869). Similar mechanisms probably apply to the enzymatic C alpha-C beta cleavage of natural lignin.  (+info)

Possible initial steps in the catabolism of 1,2-diphenylethanone (deoxybenzoin) by Pseudomonas fluorescens DB-5. (24/26)

A natural bacterial strain, identified as Pseudomonas fluorescens DB-5, was isolated in enrichment cultures containing 1,2-diphenylethanone as the only source of carbon and energy. On the basis of characteristic features observed in the mass spectra of degradation intermediates, it is proposed that metabolism of 1,2-diphenylethanone is initiated by two hydroxylations on the benzyl ring. Phenol, presumably arising from the benzoyl ring, was transiently detected as a catabolic intermediate.  (+info)