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PubMed2000

[The compound A concentration in a low-flow anesthesia circuit using the new CO2 absorbent SPHERASORB].

CO2 absorbents convert sevoflurane to fluoromethyl-2,2-difluoro-1-(trifluoromethyl) vinyl ether (compound A), whose toxicity in rats raises concern regarding the safety of sevoflurane in a low-flow system. SPHERASORB is a new CO2 absorbent which does not contain KOH. However, the reaction between SPHERASORB and sevoflurane has not been examined. We compared compound A concentration in a model circuit using SPHERASORB and the commonly used Sodasorb II. The anesthesia circuit was circulated with fresh gas flow at a rate of 1 l.min-1 containing 2% sevoflurane. Compound A concentration was measured hourly and the temperature of CO2 absorbent was monitored. The maximum concentration of compound A in the circuit was 12.2 +/- 1.4 ppm for SPHERASORB and 18.6 +/- 0.4 ppm for Sodasorb II (P < 0.05). The maximum temperature of SPHERASORB was lower than that of Sodasorb II (P < 0.05). SPHERASORB can reduce compound A formation, compared to Sodasorb II.

Absorption↗
PubMed2002

A new pathway for hydroamination. Mechanism of palladium-catalyzed addition of anilines to vinylarenes.

The mechanism of the hydroamination of vinylarenes with anilines catalyzed by phosphine-ligated palladium triflates was uncovered. eta3-Arylethyl diphosphine palladium triflate complexes, which result from migratory insertion of vinylarene into a palladium hydride triflate, were shown to be the resting state of the catalytic cycle. A series of these complexes has been isolated and fully characterized. The [(R)-Tol-BINAP][1-(2-naphthyl)ethyl]palladium triflate derivative 1a was crystallographically characterized. This complex reacted with aniline to form the N-phenethylaniline product in 83% yield. Reaction of the benzylic derivative [(R)-Tol-BINAP](eta3-benzyl)palladium triflate with aniline also formed the N-benzylaniline product in a high 87% yield. Predominant inversion of configuration from the reaction between 1a, which is enantiopure, and aniline showed that external attack of the amine on the eta3-arylethyl ligand occurred to form the product. This product from reaction of aniline with 1a is the opposite enantiomer to that obtained from the catalytic process. Thus, a minor diastereomer gives the major enantiomer in the catalytic cycle, and the major diastereomer gives the minor enantiomer. Consistent with this assertion, kinetic studies showed that the major diastereomer formed product with a rate constant roughly 3.5 times slower than the rate constant for the catalytic process that contains all diastereomers.

Amination↗
PubMed1982

Antimicrobial characteristic of insoluble alkylpyridinium iodide.

Insoluble and soluble alkylpyridinium iodides (C8 to C18) were synthesized. The insoluble agents were quaternized 4-vinylpyridine-divinylbenzene copolymers. The insoluble agent [C12(50)] that contained 50% divinylbenzene and had a C12 alkyl chain was selected as the most suitable insoluble agent. C12(50) showed poor durability of the antibacterial activity, but C12(50), which had lost the activity, was refreshed by washing with ethanol. This washing became ineffective after a few cycles of antibacterial treatment and refreshment. Such C12(50) recovered the activity upon 1.0 N NaOH treatment. The antibacterial activity of C12(50) depended on its surface area. It showed high antimicrobial activity against gram-positive bacteria and also showed activity against gram-negative bacteria and yeasts. But the activities of C12(50) and laurylpyridinium iodide solution were different against some microbes. The antibacterial activities of the agents were investigated against Escherichia coli and Micrococcus luteus under various conditions. The activity of C12(50) was higher at a higher temperature or at a lower cell concentration. The activity of C12(50) decreased on addition of NaCl, glucose, or bovine albumin to the cell suspension or in 0.01 M sodium-potassium phosphate buffer. C12(50) showed less activity when cells were mixed with dead cells or the supernatant of dead cells killed in an autoclave. The mode of action of the laurylpyridinium iodide solution against E. coli and M. luteus was similar to that of C12(50) except for the influence of E. coli cell concentration.

Alkanes↗
PubMed2004

Zirconium-mediated cross-coupling of terminal alkynes and vinyl bromides: selective synthesis of cyclobutene and 1,3-diene derivatives.

A diastereoselective synthesis of 1,3-butadiene or cyclobutene derivatives by a zirconium-mediated reaction of alkenyllithium compounds and vinyl bromides is reported. The key steps involve the generation of zirconocene-alkyne complexes from haloalkenes and subsequent coupling with alkenyl bromides. Thus, formally the process supposes the cross-coupling reaction between a terminal alkyne and an alkenyl bromide. Moreover, the use of butyl vinyl ether instead of vinyl bromide as the unsaturated system allows an alternative access to different 1,3-butadiene regioisomers.

Journal Article↗
PubMed2003

Ruthenium-catalyzed vinylsilane synthesis and cross-coupling as a selective approach to alkenes: benzyldimethylsilyl as a robust vinylmetal functionality.

[reaction: see text] Ruthenium-catalyzed alkyne hydrosilylation or silyl-alkyne Alder ene reactions provide entry into benzyldimethylsilyl (BDMS)-substituted alkenes. The BDMS-vinylsilanes are further elaborated through mild palladium-catalyzed cross coupling and show significant stability to intervening synthetic operations, including silyl ether deprotection.

Alkenes↗
PubMed2006

Blood-brain barrier traversal by African trypanosomes requires calcium signaling induced by parasite cysteine protease.

In this study we investigated why bloodstream forms of Trypanosoma brucei gambiense cross human brain microvascular endothelial cells (BMECs), a human blood-brain barrier (BBB) model system, at much greater efficiency than do T. b. brucei. After noting that T. b. gambiense displayed higher levels of cathepsin L-like cysteine proteases, we investigated whether these enzymes contribute to parasite crossing. First, we found that T. b. gambiense crossing of human BMECs was abrogated by N-methylpiperazine-urea-Phe-homopheylalanine-vinylsulfone-benzene (K11777), an irreversible inhibitor of cathepsin L-like cysteine proteases. Affinity labeling and immunochemical studies characterized brucipain as the K11777-sensitive cysteine protease expressed at higher levels by T. b. gambiense. K11777-treated T. b. gambiense failed to elicit calcium fluxes in BMECs, suggesting that generation of activation signals for the BBB is critically dependant on brucipain activity. Strikingly, crossing of T. b. brucei across the BBB was enhanced upon incubation with brucipain-rich supernatants derived from T. b. gambiense. The effects of the conditioned medium, which correlated with ability to evoke calcium fluxes, were canceled by K11777, but not by the cathepsin B inhibitor CA074. Collectively, these in vitro studies implicate brucipain as a critical driver of T. b. gambiense transendothelial migration of the human BBB.

Animals↗
PubMed1996

Identification in rat bile of glutathione conjugates of fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether, a nephrotoxic degradate of the anesthetic agent sevoflurane.

Recent studies have indicated that the nephrotoxicity of fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether ("Compound A"), a breakdown product of the inhaled anesthetic sevoflurane, may be mediated by a reactive intermediate(s) generated via the cysteine conjugate beta-lyase pathway. In order to gain a better understanding of glutathione (GSH)-dependent metabolism of Compound A, the present study was carried out with the primary goal of detecting and characterizing Compound A--GSH conjugates. By means of ionspray LC-MS/MS and NMR spectroscopy, a total of four GSH conjugates ("A1-A4") were identified from the bile of rats dosed intraperitoneally with Compound A. A1 and A2 were identified as two diastereomers of S-[1,1-difluoro-2-(fluoromethoxy)-2-(trifluoromethyl)ethyl]glutath ione, while A3 and A4 were identified as (E)- and (Z)-S-[1-fluoro-2-(fluoromethoxy)-2-(trifluoromethyl)-vinyl]glutat hione, respectively. Quantitative analyses indicated that approximately 29% of the administered dose of Compound A was excreted into the bile in the form of the above GSH conjugates over a period of 6 h. Studies conducted in vitro demonstrated that the reaction of Compound A with GSH was catalyzed by both rat liver cytosolic and microsomal glutathione S-transferases (GST), with the two enzyme systems exhibiting different product selectivities. Formation of these GSH conjugates also occurred nonenzymatically at an appreciable rate. These results indicate that spontaneous and enzyme-mediated conjugation with GSH represents a major pathway of metabolism of Compound A in rats. Conjugation of Compound A with GSH in vivo appeared to be catalyzed preferentially by microsomal rather than cytosolic GST, based on comparison of biliary, microsomal, and cytosolic metabolic profiles. By analogy with other haloalkenes, further metabolism of the corresponding cysteine conjugates of Compound A by renal cysteine conjugate beta-lyase may lead to the formation of reactive acylating agents, which would be expected to bind covalently to cellular macromolecules and cause organ-selective nephrotoxicity.

Animals↗
PubMed2001

An efficient method for the preparation of 1'alpha-branched-chain sugar pyrimidine ribonucleosides from uridine: the first conversion of a natural nucleoside into 1'-substituted ribonucleosides.

The 1'alpha-phenylselenouridine derivative 13 was successfully synthesized by enolization of the 3',5'-O-TIPDS-2'-ketouridine 8, and was subjected to a radical reaction with a vinylsilyl tether--an efficient procedure for preparing 1'alpha-branched-chain sugar pyrimidine nucleosides. Successive treatment of 8 with LiHMDS and PhSeCl in THF at < -70 degrees C gave the desired 1'-phenylseleno products in 85% yield as an anomeric mixture of the 1'alpha-product 11 and the 1'beta-product 12 (11/12= 2.5:1). Highly stereoselective reduction at the 2'-carbonyl of the 1'alpha-product 11 occurred from the beta-face by using NaBH4/CeCl3 in MeOH, and subsequent introduction of a dimethylvinylsilyl tether at the 2'-hydroxyl gave the radical reaction substrate 14. The photochemical radical atom-transfer reaction of 14 by using a high-pressure mercury lamp proceeded effectively in benzene to give the exo-cyclized PhSe-transferred product 18, in which (PhSe)2 proved to be essential as an additive for radical atom-transfer cyclization reactions. Subsequent phenylseleno-group elimination of 18 gave the sugar-protected 1'alpha-vinyluridine. With this procedure, 1'alpha-vinyluridine (22) and -cytidine (25), designed to be potential antitumor agents, were successfully synthesized. This study is the first example of functionalization at the anomeric 1'-position of a nucleoside by starting from a natural nucleoside to produce a ribo-type 1'-modified nucleoside.

Cyclization↗
PubMed2006

A highly active palladium catalyst for intermolecular hydroamination. Factors that control reactivity and additions of functionalized anilines to dienes and vinylarenes.

We report a catalyst for intermolecular hydroamination of vinylarenes that is substantially more active for this process than catalysts published previously. With this more reactive catalyst, we demonstrate that additions of amines to vinylarenes and dienes occur in the presence of potentially reactive functional groups, such as ketones with enolizable hydrogens, free alcohols, free carboxylic acids, free amides, nitriles, and esters. The catalyst for these reactions is generated from [Pd(eta(3)-allyl)Cl](2) (with or without added AgOTf) or [Pd(CH(3)CN)(4)](BF(4))(2) and Xantphos (9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene), which generates complexes with large P-Pd-P bite angles. Studies on the rate of the C-N bond-forming step that occurs by attack of amine on an eta(3)-phenethyl and an eta(3)-allyl complex were conducted to determine the effect of the bite angle on the rate of this nucleophilic attack. Studies on model eta(3)-benzyl complexes containing various bisphosphines showed that the nucleophilic attack was faster for complexes containing larger P-Pd-P bite angles. Studies of substituted unsymmetrical and unsubstituted symmetrical model eta(3)-allyl complexes showed that nucleophilic attack on complexes ligated by Xantphos was faster than on complexes bearing ligands with smaller bite angles and that nucleophilic attack on unsymmetrical allyl complexes with larger bite angle ligands was faster than on unsymmetrical allyl complexes with smaller bite angle ligands. However, monitoring of catalytic reactions of dienes by (31)P NMR spectroscopy showed that the concentration of active catalyst was the major factor that controlled rates for reactions of symmetrical dienes catalyzed by complexes of phosphines with smaller bite angles. The identity of the counterion also affected the rate of attack: reactions of allylpalladium complexes with chloride counterion occurred faster than reactions of allylpalladium complexes with triflate or tetrafluoroborate counterion. As is often observed, the dynamics of the allyl and benzyl complexes also depended on the identity of the counterion.

Alkenes↗