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PubMed1996

Comparison of the gas-phase basicities and relative methylation nucleophilicities of carbonyl-containing compounds.

The gas-phase basicities and relative methylation nucleophilicities of a series of simple cyclic carbonyl-containing compounds were evaluated in order to understand the low reactivities of some barbiturates and anti-convulsants in the gas phase. The gas-phase basicities were determined by the bracketing method, and the relative methylation nucleophilicities were characterized by monitoring ion-molecule reactions with CH3OCH2+ ions from dimethyl ether. Heats of formation were calculated for the protonated and methylated structures in order to estimate the favored sites of protonation and methylation. As shown in this paper, the positions of the carbonyl groups have a striking effect on the relative gas-phase basicities and methylation rates within a related series of compounds. For those compounds with two carbonyl groups in 1,2 positions, the methylation efficiency is enhanced by a factor of 100 over those compounds with two carbonyl groups in the 1,3 or 1,4 positions. This large difference is attributed to the variation in molecular dipole moments of the three cyclohexanediones and the relative positions of the two carbonyl groups. Cyclohexane-1,2-dione has the greatest dipole moment, leading to the highest interaction energy with the CH3OCH2+ reactant, and has the capability for cooperative interaction during the attack on CH3OCH2+ and subsequent rapid methyl cation transfer between the two carbonyl groups, thus enhancing the reaction rate and product stability. The order of gas-phase basicities is also strongly influenced by the number and positions of the carbonyl groups and the presence of a nitrogen atom in the ring. For example, glutarimide, which has two carbonyl groups surrounding a nitrogen atom in the ring, has a gas-phase basicity that is about 10 kcal mol-1 less than that of cyclohexane-1,3-dione. This result is attributed to the restriction of partial hydrogen-bond formation between the two carbonyl groups in glutarimide because of increased planarity of the ring due to the nitrogen atom.

Anticonvulsants↗
PubMed2000

[8-(Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl], the inhibitor of intracellular calcium mobilization, blocked mitogen-induced T cell proliferation by interfering with the sustained phase of protein kinase C activation.

The physiological role of IP(3)-dependent Ca(2+) release in T cell activation was in question due to the contradictory findings that [8-(Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl] (TMB-8), an inhibitor of intracellular Ca(2+) mobilization, blocked T cell proliferation, curtailing specifically the level of released Ca(2+) did not affect T cell activation and T cell line lacking IP(3) receptor was defective in IL-2 production in response to TCR/CD3 ligand. In the present study we found that TMB-8 inhibited Concanavalin A (Con A)- but not PMA/Ionomycin-induced T cell proliferation in a reversible and dose-dependent manner. The kinetic study revealed that TMB-8 exerted the inhibitory effect at a very early step of T cell activation. The Ca(2+) ionophore ionomycin augmented instead of overcoming the inhibitory effect of TMB-8, although the same doses of ionomycin alone had no effect on Con A-induced T cell proliferation. PMA the metabolically stable, but not diacylglycerol (DAG) the metabolically labile, activator of protein Kinase C (PKC) completely overcome the antiproliferative effect of TMB-8. A specific DAG lipase inhibitor RHC80267 also overcome the effect of TMB-8. Taken together, these results showed that the process of Ca(2+) release through IP(3) receptor, not the released Ca(2+), is essential for the sustained phase of PKC activation during T cell proliferation.

Animals↗
PubMed1998

Fibroblast growth factor receptor signaling in Xenopus retinal axon extension.

Fibroblast growth factor receptors (FGFRs) and N-cadherin both regulate axon extension in developing Xenopus retinal ganglion cells (RGCs). Cultured cerebellar neurons have been shown to require FGFR activity for N-cadherin-stimulated neurite outgrowth, raising the possibility that N-cadherin is a FGFR ligand. To investigate this possibility in the developing visual system, retinal neurons were transfected with a dominant-negative FGFR (XFD) and plated on purified N-cadherin substrates. XFD-expressing neurons extended markedly shorter processes than control GFP-expressing neurons, implicating a role for FGFRs in N-cadherin-stimulated neurite outgrowth. To examine whether N-cadherin and FGFRs share the same pathway or use distinct second messenger pathways, specific inhibitors of implicated signaling molecules were added to neurons stimulated by N-cadherin, basic fibroblast growth factor (bFGF), or brain-derived nerve factor (BDNF) (which stimulates RGC outgrowth by a FGFR-independent mechanism). Diacylglycerol (DAG) lipase and Ca2+/calmodulin kinase II inhibitors both significantly reduced outgrowth stimulated by N-cadherin or bFGF but not by BDNF. Furthermore, we show that inhibiting DAG lipase activity in RGC axons extending in vivo toward the optic tectum reversibly slows axon extension without collapsing their growth cones. Thus, a common second-messenger signaling pathway mediating both N-cadherin- and bFGF-stimulated neurite extension is consistent with a model in which N-cadherin directly modulates the FGFR or a model whereby both FGFR and N-cadherin regulate the same second-messenger system.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMedDate not supplied

Quantitative TLC determination of formaldehyde in hard tissues of teeth.

Levels of formaldehyde, which is formed within cells as an indispensable part of biological processes, have been determined by means of TLC in hard tissues of human teeth, with and without pathological changes. A wide variety of formaldehyde levels was determined according to the physiological state of a tooth. The results show that caries can be of immense importance in the process of formaldehyde formation and its release in hard tissues of human teeth.

Chromatography, Thin Layer↗
PubMed1999

Measurement of formaldehyde as dimedone adduct and potential formaldehyde precursors in hard tissues of human teeth by overpressured layer chromatography.

Simple, automatic overpressured layer chromatographic methods for the parallel determination of endogenous formaldehyde in the form of dimedone adduct and potential formaldehyde generators (betaines) in hard tissues of human teeth are described together with an efficient densitometric evaluation. These simple procedures involve the special preparation of teeth and extraction of formaldehyde, of different binding force in teeth, with methanol containing dimedone, and the isolation of betaines with an aqueous solution of methanol.

Automation↗
PubMed2000

Efficient asymmetric synthesis of alpha-alkylated 1, 4-cyclohexanedione derivatives, important chiral building blocks in the synthesis of natural products.

Alkylation of 1,4-cyclohexanedione monoethylene acetal SAMP-hydrazone with various electrophiles (10 examples given) and subsequent cleavage of the hydrazones with saturated oxalic acid furnished highly enantiomerically enriched alpha-alkylated mono-protected 1,4-cyclohexanedione derivatives in high yields and enantiomeric excesses of ee = 28, 80->/=99%. Reduction of the ketones gave the corresponding alcohols in good yields with high enantiomeric excesses (ee = 80->/=98%) and cis/trans-ratios of usually 85:15.

Alcohols↗
PubMed2000

Catalysis of the addition of benzenethiol to 2-cyclohexen-1-ones by uranyl-salophen complexes: a catalytic metallocleft with high substrate specificity.

The base induced addition of benzenethiol to 2-cyclohexen-1-one and its 4,4-, 5,5- and 6,6-dimethyl derivatives is catalysed by a salophen-uranyl based metallocleft 2 in chloroform solution with high turnover efficiency and low product inhibition. Analysis of rate data coupled with equilibrium measurements for complexation of the catalyst with the enone reactants and addition products shows that the catalytic mechanism involves the three main steps typical of single-substrate enzymatic processes, namely substrate binding and recognition, transformation of the bound substrate, and release of the reaction product. Unlike the reference salophen-uranyl 1, catalyst 2 is endowed with a structured binding site responsible for a high degree of substrate specificity among the investigated enones, due to recognition of their shape and size.

Antinematodal Agents↗
PubMed2000

HPLC-OPLC-MS investigation of change of formaldehyde and its generators in human teeth of different physiological stage.

Taking into consideration the unquestionable intracellular occurrence of formaldehyde (HCHO) and its generators in cells of plant, animal and human organisms as well as in body fluids it was resolved to determine their levels in hard tissues of physiologically and pathologically changed teeth. The aim of the work was to determine the relationship between the level of HCHO and the levels of its generators in pathologically changed teeth, mainly carietic teeth as tooth caries is still a serious and commonly occurring problem. The occurrence of HCHO (captured as its dimedone adduct) and some of its potential generators was demonstrated in the hard tissues of healthy and pathological human teeth by means of OPLC, HPLC and MS analyses. It was established that the measurable level of HCHO was increased in the carietic teeth in comparison with healthy ones. In the case of paradontic tooth sample, a dramatic increase of HCHO was observed and at the same time the level of betaines was decreased considerably. The obtained results give a new insight into the pathology of hard tissues of teeth in strong correlation with the phases of stress syndrome.

Betaine↗
PubMedDate not supplied

An improved NMR method for the quantification of alpha-acids in hops and hop products.

A new and independent method for the quantification of alpha-acids in hops and hop products has been developed. NMR was used as a qualitative method for the complete assignment of all 1H- and 13C-NMR signals of the three main alpha-acids, cohumulone (1), humulone (2) and adhumulone (3). In a 13C two-dimensional INADEQUATE experiment, the 13C-NMR spectrum of 1 was unambiguously assigned via the carbon-carbon connectivities. Use of NMR as a quantitative method allowed quantification of the pure and individual alpha-acids 1 and 2, and the determination of the absolute concentration of solutions of these compounds. Quantification of alpha-acids by NMR is less complicated and more reliable than the methods used until now.

Cyclohexanones↗
PubMed2001

Mesotrione: a new selective herbicide for use in maize.

Mesotrione is a new herbicide being developed for the selective pre- and post-emergence control of a wide range of broad-leaved and grass weeds in maize (Zea mays). It is a member of the benzoylcyclohexane-1,3-dione family of herbicides, which are chemically derived from a natural phytotoxin obtained from the Californian bottlebrush plant, Callistemon citrinus. The compound acts by competitive inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), a component of the biochemical pathway that converts tyrosine to plastoquinone and alpha-tocopherol. Mesotrione is an extremely potent inhibitor of HPPD from Arabidopsis thaliana, with a Ki value of c 6-18 pM. It is rapidly taken up by weed species following foliar application, and is distributed within the plants by both acropetal and basipetal movement. Maize is tolerant to mesotrione as a consequence of selective metabolism by the crop plant. Slower uptake of mesotrione, relative to susceptible weed species, may also contribute to its utility as a selective herbicide for use in maize.

4-Hydroxyphenylpyruvate Dioxygenase↗
PubMed1978

Biosynthesis in theory and practice: structure determinations.

Classical appraoches to structure determinations of natural molecules can be assisted by biosynthetic considerations. Application of these needs some structural evidence, based on degradations and spectra, as to biogenetic type. This evidence can be effectively supplemented by incorporations of precursors labelled with 14C, 13C or 15N, as appropriate, with examinations of the distributions of label in the product. Several examples of both classical and incorporation techniques are reviewed.

Alkaloids↗
PubMed1985

Antiarthritic drugs containing thiol groups scavenge hypochlorite and inhibit its formation by myeloperoxidase from human leukocytes. A therapeutic mechanism of these drugs in rheumatoid arthritis?

We investigated the effect of antiarthritic drugs containing thiol groups, such as D-penicillamine, tiopronin (N-[2-mercaptopropionyl]glycine), sodium aurothiomalate, and aurothioglucose, on the chlorinating activity of myeloperoxidase purified from human leukocytes. Hypochlorite, the reactive product of the reaction catalyzed by myeloperoxidase, was effectively scavenged by these antiarthritic drugs, and in addition, D-penicillamine and tiopronin inhibited myeloperoxidase itself. The above-mentioned effects of these drugs were observed at concentrations that occur in the serum of rheumatoid arthritis patients treated with these agents. We suggest that the therapeutic effect of these antiarthritic drugs may be due to the protection of tissues against the reactive HOCI released by activated granulocytes at inflamed sites.

Amino Acids, Sulfur↗