Electroencephalographic patterns during anesthesia with cyclopropane; correlation with concentration of cyclopropane in arterial blood.
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Anesthesia↗
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Cyclopropane anesthesia. I. Cardiac rate and rhythm during steady levels of cyclopropane anesthesia at normal and elevated end-expiratory carbon dioxide tensions.
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Analgesia↗
Cyclopropane anesthesia. 3. Effects of cyclopropane on respiration and circulation in normal man.
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Anesthesia↗
Electronic and geometrical structures of cyclopropanes: linear correlation of ionization energies with C-C bond lengths in monosubstituted cyclopropanes.
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Journal Article↗
Three-component aldimine addition--cyclopropanation. an efficient new methodology for amino cyclopropane synthesis.
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Journal Article↗
The mmaA2 gene of Mycobacterium tuberculosis encodes the distal cyclopropane synthase of the alpha-mycolic acid.
Infection with Mycobacterium tuberculosis (Mtb) remains a severe global health problem that has prompted an aggressive search for new antibiotic targets and vaccine strategies for this persistent pathogen. Recently, a wide variety of genetic determinants of Mtb pathogenicity have been identified, including several genes involved in the biogenesis of the complex Mtb cell envelope. Among these are the mycolic acid cyclopropane synthases, a family of proteins that modify the major cell envelope lipids of Mtb with a diversity of cyclopropane rings. Despite substantial sequence identity, these proteins catalyze highly specific cyclopropane modifications, including proximal modification of the alpha-mycolate (pcaA) and trans-cyclopropane modification (cmaA2). Here we report the mycolic acid modification function of a third cyclopropane synthase, mmaA2, through the creation and analysis of an M. tuberculosis mmaA2 null mutant. Unexpectedly, mmaA2 is essential for the distal cyclopropane modification of the alpha-mycolate, a function previously attributed to cmaA1. alpha-Mycolates of a cmaA1 null mutant were unaffected, demonstrating that cmaA1 is not required for alpha-mycolate modification. Although fully cyclopropanated methoxymycolates are produced in the mmaA2 mutant, cis-cyclopropanation is impaired, leading to accumulation of unsaturated methoxymycolate derivatives. This study establishes mmaA2 as a distal cyclopropane synthase of the alpha-mycolates of M. tuberculosis and the first cyclopropane synthase to modify both alpha- and oxygenated mycolates. These results expand our knowledge of the biosynthesis of the Mtb cell envelope and will allow further elucidation of the relationship between Mtb pathogenesis and the fine structure of mycolic acids.
Genes, Bacterial↗
The biosynthesis of cyclopropanated mycolic acids in Mycobacterium tuberculosis. Identification and functional analysis of CMAS-2.
The major mycolic acid produced by Mycobacterium tuberculosis contains two cis-cyclopropanes in the meromycolate chain. The gene whose product cyclopropanates the proximal double bond was cloned by homology to a putative cyclopropane synthase identified from the Mycobacterium leprae genome sequencing project. This gene, named cma2, was sequenced and found to be 52% identical to cma1 (which cyclopropanates the distal double bond) and 73% identical to the gene from M. leprae. Both cma genes were found to be restricted in distribution to pathogenic species of mycobacteria. Expression of cma2 in Mycobacterium smegmatis resulted in the cyclopropanation of the proximal double bond in the alpha 1 series of mycolic acids. Coexpression of both cyclopropane synthases resulted in cyclopropanation of both centers, producing a molecule structurally similar to the M. tuberculosis alpha-dicyclopropyl mycolates. Differential scanning calorimetry of purified cell walls and mycolic acids demonstrated that cyclopropanation of the proximal position raised the observed transition temperature by 3 degrees C. These results suggest that cyclopropanation contributes to the structural integrity of the cell wall complex.
Amino Acid Sequence↗
Trans-cyclopropanation of mycolic acids on trehalose dimycolate suppresses Mycobacterium tuberculosis -induced inflammation and virulence.
Recent studies have shown that fine structural modifications of Mycobacterium tuberculosis cell envelope lipids mediate host cell immune activation during infection. One such alteration in lipid structure is cis-cyclopropane modification of the mycolic acids on trehalose dimycolate (TDM) mediated by proximal cyclopropane synthase of alpha mycolates (pcaA), a proinflammatory lipid modification during early infection. Here we examine the pathogenetic role and immunomodulatory function of mycolic acid cyclopropane stereochemistry by characterizing an M. tuberculosis cyclopropane-mycolic acid synthase 2 (cmaA2) null mutant (Delta cmaA2) that lacks trans-cyclopropanation of mycolic acids. Although titers of WT and Delta cmaA2 organisms were identical during mouse infection, Delta cmaA2 bacteria were hypervirulent while inducing larger granulomas than WT M. tuberculosis. The hypervirulence of the Delta cmaA2 strain depended on host TNF-alpha and IFN-gamma. Loss of trans-cyclopropanation enhanced M. tuberculosis-induced macrophage inflammatory responses, a phenotype that was transferable with petroleum ether extractable lipids. Finally, purified TDM lacking trans-cyclopropane rings was 5-fold more potent in stimulating macrophages. These results establish cmaA2-dependent trans-cyclopropanation of TDM as a suppressor of M. tuberculosis-induced inflammation and virulence. In addition, cyclopropane stereochemistries on mycolic acids interact directly with host cells to both positively and negatively influence host innate immune activation.
Animals↗
Nonhalogenated alkanes cyclopropane and butane affect neurotransmitter-gated ion channel and G-protein-coupled receptors: differential actions on GABAA and glycine receptors.
BACKGROUND: Anesthetic mechanisms of nonhalogenated alkanes cyclopropane and butane are not understood. This study was designed to look at which neurotransmitter receptors are possible targets for these anesthetics. METHODS: Effects of cyclopropane and butane on eight recombinant receptors expressed in Xenopus oocytes were examined electrophysiologically. To address molecular mechanisms of interaction with glycine and gamma-aminobutyric acid type A (GABA(A)) receptors, cyclopropane was further tested on alpha1(S267C) glycine receptor and alpha2(S270X)beta1 GABA(A) receptors that were mutated to amino acids with larger side chains. RESULTS: Cyclopropane (1, 2, and 5 minimum alveolar concentration [MAC]) potentiated glycine responses by 39, 62, and 161%, respectively, and butane (1 MAC) potentiated by 64% with an increase in apparent affinity for glycine, but yielded barely detectable potentiation of GABA(A) receptors. The efficacy of cyclopropane for glycine receptors was less than isoflurane and halothane. The potentiation by cyclopropane was eliminated for the alpha1(S267C) glycine receptor. Mutant GABA(A) receptors in which the corresponding amino acid was substituted with larger amino acids did not produce significant potentiation. Cyclopropane and butane inhibited nicotinic acetylcholine and N-methyl-D-aspartate receptors, potentiated G-protein-coupled inwardly rectifying potassium channels, and did not change 5-hydroxytryptamine(3A) or muscarinic(1) receptor function. Only cyclopropane markedly inhibited alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors. CONCLUSIONS: Glycine, nicotinic acetylcholine, and N-methyl-D-aspartate receptors are sensitive to nonhalogenated alkanes, and the authors propose that glycine and N-methyl-D-aspartate receptors are good candidates for anesthetic immobility. The authors also suggest that the distinct effects on glycine and GABA(A) receptors are not due to the small volumes of these anesthetics.
Anesthetics↗
Escherichia coli cyclopropane fatty acid synthase: is a bound bicarbonate ion the active-site base?
Cyclopropane synthases catalyze the cyclopropanation of unsaturated fatty acid using S-adenosyl-L-methionine as the methylene donor. The crystal structure of three cyclopropane synthases from Mycobacterium tuberculosis showed a bicarbonate ion bound in the active site that was proposed to act as a general base in the reaction mechanism [Huang, C., Smith, V., Glickman, M. S., Jacobs, W. R., and Sacchettini, J. C. (2002) J. Biol. Chem. 277, 11559-11569]. Because the in vitro activity of M. tuberculosis cyclopropane synthases has not yet been reported and because the ligands of the bicarbonate ion are all strictly conserved in cyclopropane synthases, we used the closely related Escherichia coli cyclopropane fatty acid synthase for this study. The putative ligands that share a hydrogen bond with the bicarbonate through their side chains were mutated. H266A, Y317F, E239A, and E239Q mutants were thus constructed and purified, and their catalytic efficiencies were 5.3, 0.7, 0.2, and <0.02%, respectively. C139 that is bound to the bicarbonate by its NH amide had already been mutated to serine in a previous work, and this mutant retains 31% of the activity of the wild-type enzyme. Kinetic analyses and binding studies using spectrofluorimetry showed that these mutations affected the catalytic constant rather than the binding of the substrates. While addition of free bicarbonate had almost no effect on the wild-type enzyme activity, all mutants, with the exception of E239A and E239Q, were rescued by the addition of free bicarbonate. The catalytic efficiencies of the rescued mutants were 85, 16, and 14% for C139S, H266A, and Y317F, respectively. This effect was specific to bicarbonate. The kinetic parameters of the rescued mutants were determined, and it is shown that the rescuing effect is due to an increase in kcat. These data are interpreted by assuming that the E. coli cyclopropane fatty acid synthase specifically binds a bicarbonate ion that is involved in catalysis, as proposed for the M. tuberculosis enzymes, and that mutation of the bicarbonate ligands decreases the affinity for that ion. However, because the E239Q mutation could not be rescued, we propose that E239 forms a catalytic dyad with the bicarbonate to perform the proton abstraction necessary in the chemical pathway to the cyclopropane ring.
Bicarbonates↗
Asymmetric inter- and intramolecular cyclopropanation of alkenes catalyzed by chiral ruthenium porphyrins. Synthesis and crystal structure of a chiral metalloporphyrin carbene complex.
Extensive investigations of asymmetric intermolecular cyclopropanation of terminal alkenes with diazoacetates catalyzed by ruthenium porphyrin [Ru(P*)(CO)(EtOH)] (1, H2P = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9-yl]porphyrin) and the application of catalyst 1 to asymmetric intramolecular cyclopropanation of allylic or homoallylic diazoacetates are described. The intermolecular cyclopropanation of styrene and its derivatives with ethyl diazoacetate afforded the corresponding cyclopropyl esters in up to 98% ee with high trans/cis ratios of up to 36 and extremely high catalyst turnovers of up to 1.1 x 10(4). Examination of the effects of temperature, diazoacetate, solvent, and substituent in the intermolecular cyclopropanation reveals that (i) both enantioselectivity and trans selectivity increase with decreasing temperature, (ii) sterically encumbered diazoacetates N2CHCO2R, such as R = Bu(t), and donor solvents, such as diethyl ether and tetrahydrofuran, are beneficial to the trans selectivity, and (iii) electron-donating para substituents on styrene accelerate the cyclopropanations, with the log(k(X)/k(H)) vs sigma(+) plot for para-substituted styrenes p-X-C6H4CH=CH2 (X = MeO, Me, Cl, CF3) exhibiting good linearity with a small negative rho(+) value of -0.44 +/- 0.09. In the case of intramolecular cyclopropanation, complex 1 promoted the decomposition of a series of allylic diazoacetates to form the cyclopropyl lactones in up to 85% ee, contributing the first efficient metalloporphyrin catalyst for an asymmetric intramolecular cyclopropanation. Both the inter- and intramolecular cyclopropanations were proposed to proceed via a reactive chiral ruthenium carbene intermediate. The enantioselectivities in these processes were rationalized on the basis of the X-ray crystal structures of closely related stable chiral carbene complexes [Ru(P*)(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CH=CH2)] (3) obtained from reactions of complex 1 with N2CPh2 and N2C(Ph)CO2CH2CH=CH2, respectively.
Journal Article↗
Isotope effects and the nature of selectivity in rhodium-catalyzed cyclopropanations.
The mechanism of the dirhodium tetracarboxylate catalyzed cyclopropanation of alkenes with both unsubstituted diazoacetates and vinyl- and phenyldiazoacetates was studied by a combination of (13)C kinetic isotope effects and density functional theory calculations. The cyclopropanation of styrene with methyl phenyldiazoacetate catalyzed by Rh(2)(octanoate)(4) exhibits a substantial (13)C isotope effect (1.024) at the terminal olefinic carbon and a smaller isotope effect (1.003-1.004) at the internal olefinic carbon. This is consistent with a highly asynchronous cyclopropanation process. Very similar isotope effects were observed in a bisrhodium tetrakis[(S)-N-(dodecylbenzenesulfonyl)prolinate] (Rh(2)(S-DOSP)(4) catalyzed reaction, suggesting that the chiral catalyst engages in a very similar cyclopropanation transition-state geometry. Cyclopropanation with ethyl diazoacetate was concluded to involve an earlier transition state, based on a smaller terminal olefinic isotope effect (1.012-1.015). Density functional theory calculations (B3LYP) predict a reaction pathway involving complexation of the diazoesters to rhodium, loss of N(2) to afford a rhodium carbenoid, and an asynchronous but concerted cyclopropanation transition state. The isotope effects predicted for reaction of a phenyl-substituted rhodium carbenoid with styrene match within the error of the experimental values, supporting the accuracy of the theoretical calculations and the rhodium carbenoid mechanism. The accuracy of the calculations is additionally supported by excellent predictions of reaction barriers, stereoselectivity, and reactivity trends. The nature of alkene selectivity and diastereoselectivity effects in these reactions is discussed, and a new model for enantioselectivity in Rh(2)(S-DOSP)(4)-catalyzed cyclopropanations is presented.
Alkenes↗
Cyclopropane-derived peptidomimetics. design, synthesis, and evaluation of novel Ras farnesyltransferase inhibitors.
Trisubstituted cyclopropanes have previously been established as rigid replacements of dipeptide arrays in several biological systems. Toward further evaluating the utility of these dipeptide mimics in the design of novel CA(1)A(2)X-based inhibitors of Ras farnesyltransferase (FTase), the conformationally constrained, diastereomeric pseudopeptides CAbuPsi[COcpCO]FM 7-9, the flexible analogue CAbuPsi[CHOHCH(2)]FM (10), and the tetrapeptide CAbuFM (6) were prepared. The orientations of the two peptide backbone substituents and the phenyl group on the cyclopropane rings in 7-9were specifically designed to probe selected topological features of the hydrophobic binding pocket of the A(2) subsite of FTase. The syntheses of the requisite trisubstituted cyclopropane carboxylic acid 22 and the diastereomeric cyclopropyl lactones 32a,b featured diastereoselective intramolecular cyclopropanations of chiral allylic diazoacetates and a new method for introducing side chains onto the C-terminal amino acid of cyclopropane-derived dipeptide replacements via the opening of an N-Boc-aziridine with an organocuprate. These cyclopropane intermediates were then converted into the targeted FTase inhibitors 7-9 by standard peptide coupling techniques. The pseudopeptides 7-9 were found to be competitive inhibitors of Ras FTase with IC(50)s of 1055 nM for 7, 760 nM for 8, and 7200 nM for 9. The flexible analogue 10 of these constrained inhibitors exhibited a IC(50) of 320 nM and hence was slightly more potent than 7 and 8. All of these pseudopeptides were less potent than the tetrapeptide parent CAbuFM (6), which had an IC(50) of 38 nM. Because 7 and 8 are approximately equipotent, it appears that the orientation of the peptide backbone substituents on the cyclopropane rings in 7 and 8 do not have any significant effect on binding affinity and that multiple binding modes are possible without significant changes in affinity. On the other hand, this flexibility does not extend to the orientation of the side chain of the A(2) residue as 7 and 8 were both nearly 1 order of magnitude more potent than 9. Comparison of the relative potencies of 6 and 10 suggests that the amide linkage between the A(1) and the A(2) residues of CA(1)A(2)X-derived FTase inhibitors is important.
Alkyl and Aryl Transferases↗
The effects of cyclopropane carboxylate on hepatic pyruvate metabolism.
The effects of cyclopropane carboxylate on gluconeogenesis and pyruvate decarboxylation from [1-14C]-labeled pyruvate and lactate were investigated in perfused livers from fasted rats. With high concentrations of pyruvate (greater than or equal to 0.5 mM) in the perfusion medium, infusion of cyclopropane carboxylate inhibited pyruvate decarboxylation and gluconeogenesis by 30 and 40%, respectively. With low, more physiological concentrations of pyruvate (50 microM) or with lactate (1 mM), cyclopropane carboxylate, at a concentration which elicits maximal inhibition of pyruvate decarboxylation from pyruvate (greater than or equal to 0.5 mM), did not affect either pyruvate decarboxylation or gluconeogenesis. Evidence is presented for the rapid formation of the coenzyme-A ester of cyclopropane carboxylate in perfused livers. Infusion of l-(-)carnitine (20 mM) prevented the inhibitory effects of cyclopropane carboxylate on pyruvate decarboxylation and gluconeogenesis from pyruvate (greater than or equal to 0.5 mM). Interestingly, no decrease in the tissue level of cyclopropanecarboxyl-CoA occurs under these conditions. The present study suggests that cyclopropane carboxylate, through a presently ill-defined mediator, inhibits pyruvate decarboxylation and gluconeogenesis by interfering with the pyruvate----oxalacetate----phosphoenolpyruvate----pyruvate cycle when pyruvate (greater than or equal to 0.5mM) supports gluconeogenesis.
Acyl Coenzyme A↗
Positional specificity of cyclopropane ring formation from cis-octadecenoic acid isomers in Escherichia coli.
An unsaturated fatty acid auxotroph of Escherichia coli was grown with a series of cis-octadecenoate isomers in which the location of the double bond varied from positions 3 to 17. Each of these fatty acid isomers was incorporated into the cellular lipids, but cyclopropane derivatives were formed to at least a 3-fold greater extent from the cis-9 and cis-11 isomers than from any other positional isomers. The extent of cyclopropane acid formation was observed to be highly dependent on the rate of shaking of the culture. A culture shaking at 340 rev./min converted 8.7% of its oleate to the cyclopropane derivative at stationary phase, whereas a parallel culture shaken at 110 rev./min converted 66% of the oleate to a cyclopropane acid. The inability to observe selectivity or form derivatives from isomers other than the cis-9 and cis-11 isomers seems to be due to enzyme specificity rather than a secondary affect of the abnormal unconverted fatty acids on the cell, because the cis-9 isomer is converted to its cyclopropane derivative even in cells grown with abnormal unreactive positional isomers. The preferred substrates for cyclopropanecarboxylic acid formation contained a cis ethylenic bond at either the 9 position or the (n-7) position. In combination with results of previous studies the specificity reported here supports a concetpt that two different enzymes may participate in cyclopropane ring synthesis. One enzyme activity may recognize its substrate by the distance from the pi-bond to the carboxyl group and the other by the distance to the methyl group.
Cell Division↗
The effects of cyclopropane carboxylic acid on hepatic pyruvate metabolism.
The effects of the hypoglycemic agent, cyclopropane carboxylate, on the metabolism of various substrates that enter the mitochondrion via the mitochondrial monocarboxylate transporter were investigated in perfused rat livers. Metabolism of pyruvate, branched-chain alpha-keto acids, acetoacetate and, to a lesser extent beta-hydroxybutyrate, were all inhibited by cyclopropane carboxylate. In addition, the stimulation of pyruvate decarboxylation by beta-hydroxybutyrate at low pyruvate concentrations because of exchange of extramitochondrial pyruvate with intramitochondrially generated acetoacetate, was abolished by cyclopropane carboxylate. Gluconeogenesis from alanine, which is not transported via the monocarboxylate translocator, was not inhibited by low concentrations of cyclopropane carboxylate. Cyclopropane carboxylate also inhibited fatty acid oxidation, as measured by ketone body production. These results support previous findings that the hypoglycemic agent, cyclopropane carboxylate, exerts at least some of its metabolic effects at the level of the mitochondrial monocarboxylate transporter.
Animals↗
1,2,3-trisubstituted cyclopropanes as conformationally restricted peptide isosteres: application to the design and synthesis of novel renin inhibitors.
The 1,2,3-trisubstituted cyclopropanes 6 and 7 are the first members of a novel class of isosteric replacements for peptide linkages that are more generally represented by the dipeptide mimics 2 and 3. These unique peptide surrogates are specifically designed to lock a section of a peptide backbone in an extended beta-strand conformation (phi-angle restriction) while simultaneously enforcing one of two specifically defined orientations for the amino acid side chain (chi 1-angle restriction). Methods were first developed for the stereoselective, asymmetric synthesis of the trisubstituted cyclopropanes 15a-d, 18a-d, 22a-d, and 23a-d (Scheme II), by an efficient approach featuring the Rh2(S-MEPY)4 (11) and Rh2(R-MEPY)4 (20) catalyzed cyclization of the allylic diazoacetates 10a-d to give the optically active lactones 12a-d and 21a-d, respectively, in up to greater than or equal to 94% enantiomeric excess. Nucleophilic opening of the lactone ring of 12a-d gave the corresponding morpholine amides 14a-d. By exploiting tactics that allowed for selective epimerization of one of the two functionalized side chains on the cyclopropane nucleus, 14a-d were transformed into the two series of diastereoisomeric morpholine amide carboxylic acids 15a-d and 18a-d. Epimerization of the morpholine amide group on 14a-d followed by Jones oxidation of the intermediate alcohols gave 15a-d. Alternatively, initial oxidation of the primary alcohol groups in 14a-d followed by selective, base-catalyzed inversion alpha to the aldehyde function and then Jones oxidation gave the diastereomeric dicarboxylic acid derivatives 18a-d. In a similar fashion, the enantiomeric lactones 21a-d were converted into the two corresponding enantiomeric series of dicarboxylic acid derivatives 22a-d and 23a-d. Inhibitors of aspartic proteinases, of which renin is a typical example, are known to bind to the enzyme active site cleft in an extended conformation. Thus, in order to evaluate the efficacy of 1,2,3-trisubstituted cyclopropanes as rigid replacements of beta-strand secondary structure in pseudopeptidic ligands, 15a-d, 18a-d, 22a-d, and 23a-d were incorporated at the P3 subsite of the potential renin inhibitors 24a-h and 25a-h by coupling with the tripeptide replacement 8. A significant number of substances inhibited renin at nanomolar concentrations. On the basis of this preliminary test, 1,2,3-trisubstituted cyclopropanes do appear to constitute a viable new class of peptide mimics. Since the stereochemistry at each carbon on the cyclopropane ring may be altered, these novel replacements may also function as stereochemical probes to establish the conformation of pseudopeptide ligands bound to their macromolecular targets.
Amino Acid Sequence↗
The cardiovascular effects of cyclopropane in the intact, decerebrate and pithed rabbit preparations.
1 The anaesthetic cyclopropane was given to intact, decerebrate and pithed unanaesthetized rabbit preparations to determine the relative importance in vivo of its central and peripheral cardiovascular effects. 2 Cyclopropane elevated both the heart rate and the mean arterial pressure in the intact rabbit. 3 In the decerebrate rabbit, cyclopropane elevated the heart rate and efferent cervical preganglionic nerve activity and diminished the magnitude of these components of the aortic baroreceptor reflex, the mean arterial pressure being unaffected. 4 Apart from slight myocardial depression, cyclopropane was largely without effect in the pithed rabbit. 5 It is concluded that cyclopropane produces its cardiovascular effects by supra-collicular activation eliciting an elevation of mean arterial pressure, a central sub-collicular activation producing an increase in heart rate, and that in vivo the peripheral effects of cyclopropane are of minimal importance in comparison to these central effects.
Animals↗