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PubMed1966

The effects of cyclopropane, halothane and ether on central baroreceptor pathways.

1. The reductions in arterial pressure and preganglionic sympathetic activity evoked by aortic nerve stimulation in the rabbit were studied before and during administration of constant inspired concentrations of the inhalation anaesthetics cyclopropane, halothane, and ether. The background anaesthetic was pentobarbitone, gallamine triethiodide was given, and pulmonary ventilation was with 100% oxygen.2. During light pentobarbitone anaesthesia, aortic nerve stimulation usually induced similar reductions in arterial pressure and preganglionic discharge, expressed as the maximum percentage reduction from prestimulation levels. There were two components in the sympathetic responses, attributable to A and C fibre excitation in the aortic nerve, which was also shown to contain a third fibre group with properties similar to those of B fibres.3. The arterial pressure, heart rate, and preganglionic sympathetic responses to aortic nerve stimulation were rapidly and profoundly inhibited by 50% cyclopropane, which also produced arterial hypertension.4. Halothane (3%) significantly inhibited the depressor responses, but even in the presence of severe hypotension the arterial pressure could usually be further reduced by aortic nerve stimulation. The inhibitory effects of 2% halothane were slow in onset and not pronounced. In the concentrations used, these actions of halothane were significantly less than those of cyclopropane.5. The inhibitory effects of ether on the depressor responses were roughly intermediate between those of cyclopropane and halothane; complete suppression of the responses occurred with high ether concentrations, which were also liable to cause circulatory collapse.6. It is concluded that the three anaesthetics significantly inhibit impulse transmission through central baroreceptor pathways; the implications of the findings are discussed in relation to the different circulatory actions of these anaesthetics.

Action Potentials↗
PubMed2003

Expression of a cloned cyclopropane fatty acid synthase gene reduces solvent formation in Clostridium acetobutylicum ATCC 824.

The cyclopropane fatty acid synthase gene (cfa) of Clostridium acetobutylicum ATCC 824 was cloned and overexpressed under the control of the clostridial ptb promoter. The function of the cfa gene was confirmed by complementation of an Escherichia coli cfa-deficient strain in terms of fatty acid composition and growth rate under solvent stress. Constructs expressing cfa were introduced into C. acetobutylicum hosts and cultured in rich glucose broth in static flasks without pH control. Overexpression of the cfa gene in the wild type and in a butyrate kinase-deficient strain increased the cyclopropane fatty acid content of early-log-phase cells as well as initial acid and butanol resistance. However, solvent production in the cfa-overexpressing strain was considerably decreased, while acetate and butyrate levels remained high. The findings suggest that overexpression of cfa results in changes in membrane properties that dampen the full induction of solventogenesis. The overexpression of a marR homologous gene preceding the cfa gene in the clostridial genome resulted in reduced cyclopropane fatty acid accumulation.

1-Propanol↗
PubMedDate not supplied

Comparative effects of dextroamphetamine and reserpine on halothane and cyclopropane anesthetic requirements.

Cyclopropane minimum alveolar concentration (MAC) values in dogs following intravenous administration of 0.5, 1 or 2 mg/kg of dextroamphetamine were 27.8, 28.4, and 28.4 volumes percent, respectively. Those values did not differ significantly from each other but were 44 percent greater than average control (no dextroamphetamine(MAC values. Halothane MAC values following the same dextroamphetamine doses were 1.51, 1.71, and 1.64 volumes percent. These values were 75 percent greater than average controls, and this increase was significantly more than the 44 percent noted with cyclopropane. In contrast, 2 mg/kg of reserpine decreased halothane MAC 20 percent vut decreased cyclopropane MAC 40 percent- the difference between the two anesthetics again being statistically significant. These results suggest that alteration of anesthetic potency by centrally active adrenergic drugs depends on the sympathetic activity induced by the anesthetic. Conversely, this suggests that anesthetics may influence their own potency by altering central nervous system adrenergic activity.

Animals↗
PubMed2003

Electronically tuned chiral ruthenium porphyrins: extremely stable and selective catalysts for asymmetric epoxidation and cyclopropanation.

We report the use of three enantiomerically pure and electronically tuned ruthenium carbonyl porphyrin catalysts for the asymmetric cyclopropanation and epoxidation of a variety of olefinic substrates. The D(4)-symmetric ligands carry a methoxy, a methyl or a trifluoromethyl group at the 10-position of each of the 9-[anti-(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene)]-substituents at the meso-positions of the porphyrin. Introduction of a CF(3)-substituent in this remote position resulted in greatly improved catalyst stability, and turnover numbers of up to 7500 were achieved for cyclopropanation, and up to 14,200 for epoxidation, with ee values typically >90 % and approximately equal to 80 %, respectively. In one example, the axial CO ligand at the ruthenium was exchanged for PF(3), resulting in the first chiral ruthenium porphyrin with a PF(3) ligand reported to date. In cyclopropanations with ethyl diazoacetate, the latter catalyst performed exceedingly well, and gave a 95 % ee in the case of 1,1-diphenylethylene as substrate.

Journal Article↗
PubMed2004

Theoretical insights into the role of a counterion in copper-catalyzed enantioselective cyclopropanation reactions.

The effect of a coordinating counteranion on the mechanism of Cu(I)-catalyzed cyclopropanation has been investigated extensively for a medium-sized reaction model by means of theoretical calculations at the B3LYP/6-31G(d) level. The main mechanistic features are similar to those found for the cationic (without a counteranion) mechanism, the rate-limiting step being nitrogen extrusion from a catalyst-diazoester complex to generate a copper-carbene intermediate. The cyclopropanation step takes place through a direct carbene insertion of the metal-carbene species to yield a catalyst-product complex, which can finally regenerate the starting complex. However, the presence of the counteranion has a noticeable influence on the calculated geometries of all the intermediates and transition structures. Furthermore, the existence of a preequilibrium with a dimeric form of the catalyst, together with a higher activation barrier in the insertion step, explains the lower yield of cyclopropane products observed experimentally in the presence of chloride counterion. The stereochemical predictions of a more realistic model (made by considering a chiral bis(oxazoline)-copper(i) catalyst) have been rationalized in terms of the lack of significant steric repulsions, and the model shows good agreement with the low enantioselectivities observed experimentally for these kinds of catalytic systems.

Journal Article↗
PubMed2000

A novel mycolic acid cyclopropane synthetase is required for cording, persistence, and virulence of Mycobacterium tuberculosis.

Colonial morphology of pathogenic bacteria is often associated with virulence. For M. tuberculosis, the causative agent of tuberculosis (TB), virulence is correlated with the formation of serpentine cords, a morphology that was first noted by Koch. We identified a mycobacterial gene, pcaA, that we show is required for cording and mycolic acid cyclopropane ring synthesis in the cell wall of both BCG and M. tuberculosis. Furthermore, we show that mutants of pcaA fail to persist within and kill infected mice despite normal initial replication. These results indicate that a novel member of a family of cyclopropane synthetases is necessary for lethal chronic persistent M. tuberculosis infection and define a role for cyclopropanated lipids in bacterial pathogenesis.

Animals↗
PubMed2001

Mechanism of olefin cyclopropanation by diazomethane catalyzed by palladium dicarboxylates: a density functional study.

The reaction of diazomethane with ethylene in the presence of palladium diformate has been studied through density functional calculations. Several mechanistic paths leading to the formation of cyclopropane have been studied. The results obtained show that the reaction of palladium diformate with diazomethane is more favorable than the reaction with ethylene. The reaction with diazomethane may lead to two different isomeric complexes: a methylene-inserted complex and a palladium-carbene complex. Insertion of methylene is the most favorable process, but the resulting complex is not suitable for cyclopropanation. The reaction with two additional diazomethane molecules makes the formation of the bismethylene-inserted palladium-carbene complex favorable. Attack of ethylene on this palladium-carbene complex leads to the formation of cyclopropane.

Journal Article↗
PubMed2002

Novel approach for catalytic cyclopropanation of alkenes via (2-furyl)carbene complexes from 1-benzoyl-cis-1-buten-3-yne.

The reaction of conjugated ene-yne-ketones 3 with a variety of alkenes in the presence of a catalytic amount of Cr(CO)(5)(THF) at room temperature gives (2-furyl)cyclopropanes in good yields. These cyclopropanation reactions proceed via (2-furyl)carbene-chromium intermediates 4 formed in situ from ene-yne-ketones 3. Late transition metals, such as [RuCl(2)(CO)(3)](2), [RhCl(cod)](2), PdCl(2), and PtCl(2), also catalyze effectively the cyclopropanation of styrene with 3.

Journal Article↗
PubMed2005

The activity of Escherichia coli cyclopropane fatty acid synthase depends on the presence of bicarbonate.

Cyclopropane fatty acid (CFA) synthases catalyze the formation of cyclopropane rings on isolated and unactivated olefinic bonds within various fatty acids; the methylene carbon is derived from the activated methyl group of (S)-adenosylmethionine. The E. coli enzyme is the prototype for this class of enzymes, which include the cyclopropane mycolic acid (CMA) synthases, which are potential targets for the design of antituberculosis agents. Crystal structures of several CMA synthases have recently been solved, and electron density attributed to a bicarbonate ion was found in or near the active site. Because a functional assay for CMA synthases has not been developed, the relevance of the bicarbonate ion has not been established. CFA synthase is 30-35% identical to the CMA synthases that have been analyzed structurally, suggesting that the mechanisms of these enzymes are conserved. In this work, we show that indeed the activity of CFA synthase requires bicarbonate, and that it is inhibited by borate, a planar trigonal molecule that mimics the structure of bicarbonate. We also show that substitutions of the conserved amino acids that act as ligands to the bicarbonate ion based on the structure of CMA synthases result in drastic losses in the activity of the protein.

Bicarbonates↗
PubMed2005

Enantiospecific Sn(II)- and Sn(IV)-catalyzed cycloadditions of aldehydes and donor-acceptor cyclopropanes.

A cycloaddition strategy for the synthesis of highly enantioenriched 2,5-cis-disubstituted tetrahydrofurans has been developed. In the presence of catalytic Sn(OTf)2 or SnCl4, a range of aldehydes will undergo formal [3 + 2] cycloadditions with a scalemic donor-acceptor cyclopropane to form optically active heterocycles. Mechanistic studies support an unusual SN2 attack by the aldehyde on the activated cyclopropane. Through this mechanism, stereochemical information contained in the cyclopropane is effectively transferred to the tetrahydrofuran products.

Journal Article↗
PubMed2006

Vinyldiazolactone as a vinylcarbene precursor: Highly selective C-H insertion and cyclopropanation reactions.

Vinylcarbenes are versatile synthetic intermediates, capable of asymmetric cyclopropanation and insertion into unactivated C-H bonds. The vinyldiazolactone precursor to the metal vinylcarbene possesses superior stability in comparison to previously known vinyldiazoacetates and, for the first time, allows the use of Z-vinylcarbenes in asymmetric C-H insertion and cyclopropanation reactions. Dirhodium azetidinone ligated compounds are optimal catalysts. Cyclopropanation coupled with the Cope rearrangement provides access to trans-3,4-disubstituted hydroazulenes.

Alkenes↗
PubMed2002

An improved synthesis of cyclopropanes from stabilized phosphonates and 1,2-dioxines.

Addition of stabilized Horner-Wadsworth-Emmons (HWE) phosphonates to substituted 1,2-dioxines leads to diastereomerically pure di- and trisubstituted cyclopropanes in high yields and represents a viable alternative to ylides in the cyclopropanation reaction involving 1,2-dioxines. While yields are comparable, reaction times with these stabilized phosphonates were accelerated and the diastereoselectivity for this cyclopropanation reaction was significantly greater than for the previously reported examples employing ylides.

Journal Article↗
PubMed2004

A novel class of tunable zinc reagents (RXZnCH2Y) for efficient cyclopropanation of olefins.

A class of zinc reagents (RXZnCH(2)Y) generated with an appropriate organozinc is very effective for the cyclopropanation of olefins. The reactivity and selectivity of these reagents can be regulated by tuning the electronic and steric nature of the RX group on Zn. A reasonable level of enantioselectivity was obtained for the cyclopropanation of unfunctionalized olefins when a chiral (iodomethyl)zinc species was used, providing a valuable approach for the asymmetric cyclopropanation of unfunctionalized olefins.

Journal Article↗
PubMed2003

Ruthenium-catalyzed cyclopropanation of alkenes using propargylic carboxylates as precursors of vinylcarbenoids.

Intermolecular cyclopropanation reactions of various alkenes with propargylic carboxylates 1 are catalyzed by [RuCl2(CO)3]2 to give vinylcyclopropanes 2 in good yields. The key intermediate of the reaction is a vinylcarbene complex generated in situ by nucleophilic attack of a carbonyl oxygen of the carboxylates to an internal carbon of the alkyne activated by the ruthenium complex. A variety of transition-metal compounds other than the Ru compound can also be employed in this system. Similar cyclopropanation proceeds with conjugated dienes as well to give trans-vic-divinylcyclopropane derivatives and cycloheptadiene derivatives 5, the latter being thermally derived from the initially formed cis-vic-isomers via Cope-type rearrangement. The present reaction is chemically equivalent to the transition metal-catalyzed cyclopropanation reaction using alpha-diazoketones as carbenoid precursors.

Journal Article↗
PubMed2003

Diastereoselective and enantioselective cyclopropanation of alkenes catalyzed by cobalt porphyrins.

Cobalt(II) porphyrin complexes were shown to be general and efficient catalysts for selective cyclopropanation of alkenes with ethyl diazoacetate (EDA). The catalytic system can operate with alkenes as limiting reagents, requiring only stoichiometric amounts of EDA. The protocol is performed in one-pot fashion without the need of slow addition of EDA. The diastereoselectivity of the current system can be tuned by using different porphyrin ligands or additives, giving either trans- or cis-dominant cyclopropanes. The asymmetric cyclopropanation was also demonstrated with the use of chiral cobalt porphyrin complexes.

Journal Article↗
PubMed2004

Catalytic cyclopropanation of alkenes via (2-furyl)carbene complexes from 1-benzoyl-cis-1-buten-3-yne with transition metal compounds.

The reaction of alkenes with conjugated ene-yne-ketones, such as 1-benzoyl-2-ethynylcycloalkenes, with a catalytic amount of Cr(CO)(5)(THF) gave 5-phenyl-2-furylcyclopropane derivatives in good yields. The key intermediate of this cyclopropanation is a (2-furyl)carbene complex generated by a nucleophilic attack of carbonyl oxygen to an internal alkyne carbon in pi-alkyne complex or sigma-vinyl cationic complex. A wide range of late transition metal compounds, such as [RuCl(2)(CO)(3)](2), [RhCl(cod)](2), [Rh(OAc)(2)](2), PdCl(2), and PtCl(2), also catalyzes the cyclopropanation of alkenes with ene-yne-ketones effectively. When the reactions were carried out with dienes as a carbene acceptor, the more substituted or more electron-rich alkene moiety was selectively cyclopropanated with the (2-furyl)carbenoid intermediate.

Journal Article↗
PubMed2006

CpRuCl(PPh3)2-catalyzed cyclopropanation of bicyclic alkenes with tertiary propargylic acetates.

The electron-rich cyclopentadienylruthenium complex CpRuCl(PPh3)2 turns out to be an efficient catalyst for the regio- and stereoselective cyclopropanation of bicyclic alkenes with tertiary propargylic carboxylates. The reaction provides 1,2,3-trisubstituted cyclopropanes in high yields as a single stereoisomer instead of the expected cyclobutenes via [2 + 2] cycloaddition. Functional groups such as ethers, esters, alcohols, phenols, ketones, esters, carboxylic anhydrides, nitriles, halides, sulfones, imides, carbamates, and azines are tolerated with the catalyzed reaction. An efficient cyclopropanation of cyclobutenes was also demonstrated, providing the strained bicyclo[2.1.0(1,3)]pentane framework.

Journal Article↗