Chemoenzymatic synthesis of chiral 2,2'-bipyridine ligands and their N-oxide derivatives: applications in the asymmetric aminolysis of epoxides and asymmetric allylation of aldehydes.

A series of enantiopure 2,2'-bipyridines have been synthesised from the corresponding cis-dihydrodiol metabolites of 2-chloroquinolines. Several of the resulting hydroxylated 2,2'-bipyridines were found to be useful chiral ligands for the asymmetric aminolysis of meso-epoxides leading to the formation of enantioenriched amino alcohols (-->84% ee). N-oxide and N,N'-dioxide derivatives of these 2,2'-bipyridines, including separable atropisomers, have been synthesised and used as enantioselective organocatalysts in the asymmetric allylation of aldehydes to give allylic alcohols (-->86% ee).

Azaspiracid: first evidence of protein binding in shellfish.

The occurrence of azaspiracid (AZA) toxins in contaminated shellfish has been the focus of much research. The present study investigated the binding properties of these toxins in mussels of the species Mytilus edulis. The work involved extraction of proteins and AZAs from contaminated mussel hepatopancreas and examination of the extracts by isoelectric focusing (IEF), size exclusion chromatography (SEC) and sodium docecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Liquid chromatography coupled with tandem mass spectrometry analysis (LC-MS/MS) was also performed in this study to identify AZAs. Blank mussels were subjected to the same purification and analytical procedures. AZAs were found to be weakly bound to a protein with a molecular weight of 45 kDa, in samples of contaminated mussels. This protein, which was abundant in contaminated mussels, was also present in blank mussels, albeit at much lower concentrations. It was further noted that a 22 kDa protein was also present only in contaminated mussel samples.

Chiral aspects of the human metabolism of ethosuximide.

Ethosuximide is a chiral drug substance primarily indicated for the treatment of absence seizures. This drug is used clinically as the racemate. The human urinary metabolites of ethosuximide (I) have been studied using chiral gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The metabolites identified were the previously reported unchanged ethosuximide (I) enantiomers, all four stereoisomers of 2-(1-hydroxyethyl)-2-methylsuccinimide (II), and the four stereoisomers of 2-ethyl-3-hydroxy-2-methylsuccinimide (III). Through chemical derivatization methodology and GC/MS (using electron impact ionization [EI] and chemical ionization [CI] techniques) two enantiomers of a previously unreported metabolite of ethosuximide, 2-ethyl-2-hydroxymethylsuccinimide (VI), have been identified.

The distinctive isotopic signature of plant-derived chloromethane: possible application in constraining the atmospheric chloromethane budget.

Chloromethane (CH(3)Cl) is the most abundant halocarbon in the atmosphere. Although largely of natural origin it is responsible for around 17% of chlorine-catalysed ozone destruction. Sources identified to date include biomass burning, oceanic emissions, wood-rotting fungi, higher plants and most recently tropical ferns. Current estimates reveal a shortfall of around 2 million ty(-1) in sources versus sinks for the halocarbon. It is possible that emissions from green plants have been substantially underestimated. A potentially valuable tool for validating emission flux estimates is comparison of the delta13C value of atmospheric CH(3)Cl with those of CH(3)Cl from the various sources. Here we report delta13C values for CH(3)Cl released by two species of tropical ferns and show that the isotopic signature of CH(3)Cl from pteridophytes like that of CH(3)Cl from higher plants is quite different from that of CH(3)Cl produced by biomass burning, fungi and industry. delta13C values for CH(3)Cl produced by Cyathea smithii and Angiopteris evecta were respectively -72.7 per thousand and -69.3 per thousand representing depletions relative to plant biomass of 42.3 per thousand and 43.4 per thousand. The characteristic isotopic signature of CH(3)Cl released by green plants should help constrain their contribution to the atmospheric burden when reliable delta13C values for all other major sources of CH(3)Cl are obtained and a globally averaged delta13C value for atmospheric CH(3)Cl is available.

Quantification of urinary excretion of ethosuximide enantiomers and their major metabolites in the rat.

A chiral gas chromatographic assay has been developed for quantitative analysis of ethosuximide and its major metabolites in rat urine. The extraction procedure was found to be precise and reproducible. Recovery was in the range of 94-98%, intraday CV(%) was 0.92% for (S)-ethosuximide (50 microg/ml) and 0.51% for (R)-ethosuximide (50 microg/ml). Interday CV(%) was 1.12% for (S)-ethosuximide and 0.72% for (R)-ethosuximide. The limit of detection was determined to be around 0.01 microg/ml for each enantiomer. Following administration of rac-ethosuximide by i.v., i.p. and oral routes, unchanged ethosuximide was detected in urine up to 72 h after drug administration. The appearance of all detected metabolites occurred within 24 h of drug administration. Significantly more (S)-ethosuximide was excreted unchanged than (R)-ethosuximide with all three routes studied. A substantial amount of the drug was eliminated as the 2-(1-hydroxyethyl)-2-methylsuccinimide (2 pairs of diastereoisomers). Much less drug was eliminated as the 2-ethyl-3-hydroxy-2-methylsuccinimide with only one diastereoisomer observed. Examination of the one pair of diastereoisomers of 2-(1-hydroxyethyl)-2-methylsuccinimide that was resolved showed preferential excretion of one isomer. Comparison of both pairs of diastereoisomers showed that one pair was formed in preference to the other with a ratio of approximately 0.8:1. It is concluded that stereoselective metabolism of ethosuximide occurs.

Isolation of lipid and 2-alkylcyclobutanones from irradiated foods by supercritical fluid extraction.

The 2-alkylcyclobutanone method was adopted as a European Standard (EN1785) and MAFF Validated Method (MAFF V37) in 1996 for the detection of irradiated food containing fat. As the method requires a relatively long period (ca 2 days) of time for extraction of the 2-alkylcyclobutanones from a foodstuff, a means was sought to increase the speed at which these irradiation markers could be isolated while at the same time decreasing the amount of organic solvents required. Thus, the technique of supercritical fluid extraction (SFE) was investigated. Results showed that SFE can be used for the rapid extraction (60 min) of lipid from irradiated foods such as chicken, pork, liquid whole egg, ground beef, and from the seeds of irradiated mango and papaya with only 10 mL n-hexane being necessary for collection of the extracted sample. A method was also developed whereby the 2-alkylcyclobutanones can be selectively extracted from irradiated foods without prior extraction of the lipid. The sample extract, in 10 mL n-hexane, is purified through a Florisil SPE cartridge which is washed with 10 mL n-hexane and the 2-alkylcyclobutanones eluted with 10 mL 2% diethyl ether in n-hexane before analysis by gas chromatography/mass spectrometry. 2-Dodecylcyclobutanone and 2-tetradecylcyclobutanone were selectively extracted from irradiated chicken meat, liquid whole egg, ground beef, and mango as well as from beef burgers and baked products containing irradiated ground beef and liquid whole egg, respectively. Using this method, samples can be analyzed for irradiation treatment within 6 h as opposed to the 2-day period required for the EN1785/MAFF V37 validated method.

Structural and functional analysis of the phosphonoacetate hydrolase (phnA) gene region in Pseudomonas fluorescens 23F.

The Pseudomonas fluorescens 23F phosphonoacetate hydrolase gene (phnA) encodes a novel carbon-phosphorus bond cleavage enzyme whose expression is independent of the phosphate status of the cell. Analysis of the regions adjacent to the phosphonoacetate hydrolase structural gene (phnA) indicated the presence of five open reading frames (ORFs). These include one (phnR) whose putative product shows high levels of homology to the LysR family of positive transcriptional regulators. Its presence was shown to be necessary for induction of the hydrolase activity. 2-Phosphonopropionate was found to be an inducer (and poor substrate) for phosphonoacetate hydrolase. Unlike phosphonoacetate, which is also an inducer of phosphonoacetate hydrolase, entry of 2-phosphonopropionate into cells appeared to be dependent on the presence of a gene (phnB) that lies immediately downstream of phnA and whose putative product shows homology to the glycerol-3-phosphate transporter. RNA analysis revealed transcripts for the phnAB and phnR operons, which are transcribed divergently; the resulting mRNAs overlapped by 29 nucleotide bases at their 5' ends. Transcripts of phnAB were detected only in cells grown in the presence of phosphonoacetate, whereas transcripts of phnR were observed in cells grown under both induced and uninduced conditions. The expression of three additional genes found in the phnA region did not appear necessary for the degradation of phosphonoacetate and 2-phosphonopropionate by either Pseudomonas putida or Escherichia coli cells.

Large carbon isotope fractionation associated with oxidation of methyl halides by methylotrophic bacteria.

The largest biological fractionations of stable carbon isotopes observed in nature occur during production of methane by methanogenic archaea. These fractionations result in substantial (as much as approximately 70 per thousand) shifts in delta(13)C relative to the initial substrate. We now report that a stable carbon isotopic fractionation of comparable magnitude (up to 70 per thousand) occurs during oxidation of methyl halides by methylotrophic bacteria. We have demonstrated biological fractionation with whole cells of three methylotrophs (strain IMB-1, strain CC495, and strain MB2) and, to a lesser extent, with the purified cobalamin-dependent methyltransferase enzyme obtained from strain CC495. Thus, the genetic similarities recently reported between methylotrophs, and methanogens with respect to their pathways for C(1)-unit metabolism are also reflected in the carbon isotopic fractionations achieved by these organisms. We found that only part of the observed fractionation of carbon isotopes could be accounted for by the activity of the corrinoid methyltransferase enzyme, suggesting fractionation by enzymes further along the degradation pathway. These observations are of potential biogeochemical significance in the application of stable carbon isotope ratios to constrain the tropospheric budgets for the ozone-depleting halocarbons, methyl bromide and methyl chloride.

Continuous flow stable isotope methods for study of delta(13)C fractionation during halomethane production and degradation.

Gas chromatography/mass spectrometry/isotope ratio mass spectrometry (GC/MS/IRMS) methods for delta(13)C measurement of the halomethanes CH(3)Cl, CH(3)Br, CH(3)I and methanethiol (CH(3)SH) during studies of their biological production, biological degradation, and abiotic reactions are presented. Optimisation of gas chromatographic parameters allowed the identification and quantification of CO(2), O(2), CH(3)Cl, CH(3)Br, CH(3)I and CH(3)SH from a single sample, and also the concurrent measurement of delta(13)C for each of the halomethanes and methanethiol. Precision of delta(13)C measurements for halomethane standards decreased (+/-0.3, +/-0.5 and +/-1.3 per thousand) with increasing mass (CH(3)Cl, CH(3)Br, CH(3)I, respectively). Given that carbon isotope effects during biological production, biological degradation and some chemical (abiotic) reactions can be as much as 100 per thousand, stable isotope analysis offers a precise method to study the global sources and sinks of these halogenated compounds that are of considerable importance to our understanding of stratospheric ozone destruction.

Carbon isotope ratios for chloromethane of biological origin: potential tool in determining biological emissions.

Chloromethane (CH3Cl) with a global atmospheric burden of 5.3 million t is the most abundant halocarbon in the atmosphere. However, the origin of ca. 50% of the estimated annual global input of 4 million t of the gas to the atmosphere has yet to be determined. As the oceanic contribution to the global CH3Cl flux is now tightly constrained, an important terrestrial source is either underestimated or unrecognized. It has recently been proposed that higher plants may represent a CH3Cl source of sufficient magnitude to resolve the global budget imbalance. A potentially useful tool in validating CH3Cl emission flux estimates is comparison of the carbon isotope ratio of atmospheric CH3Cl with those of CH3Cl originating from various sources. Here we report the first measurements of delta13C for CH3Cl produced biologically. The CH3Cl released by the higher plant species Batis maritima and Solanum tuberosum was dramatically depleted in 13C with respect to plant tissue (delta13C = -36.8/1000 and -34.5/1000, respectively); CH3Cl released by the fungus Phellinus pomaceus also showed significant 13C depletion with respect to the wood growth substrate (delta13C = -17.9/1000). When reliable delta13C values for the other major sources of atmospheric CH3Cl become available, the distinctive isotopic signature of plant-derived CH3Cl should help constrain the contribution to the atmospheric burden from this source.

Biosynthetic studies on the tropane ring system of the tropane alkaloids from Datura stramonium.

Isotopic labelling experiments have been carried out in Datura stramonium root cultures with the following isotopically labelled precursors; [2H3]- [2-13C, 2H3]-, [1-13C, 18O2]-acetates, 2H2O, [2H3-methyl]-methionine, [2-13C]-phenyllactate, [3-2H]-tropine and [2'-13C, 3-2H]-littorine. The study explored the incorporation of isotope into the tropane ring system of littorine 1 and hyoscyamine 2 and revealed that deuterium from acetate is incorporated only into C-6 and C-7, and not into C-2 and C-4 as previously reported. Oxygen-18 was not retained at a detectable level into the C(3)-O bond from [1-13C, 18O2]-acetate. The intramolecular nature of the rearrangement of littorine 1 to hyoscyamine 2 is revealed again by a labelling study using [2'-13C, 3-2H]-littorine, [2-13C]-phenyllactate and [3-2H]-tropine.

Mechanisms for ion formation during the electron impact-mass spectrometry of picolinyl ester and 4,4-dimethyloxazoline derivatives of fatty acids.

Mass spectral studies have been conducted with isotopically stable labelled and fluorinated picolinyl esters and 4,4-dimethyloxazoline (DMOX) derivatives of fatty acids in order to establish mechanisms of ion formation. Reciprocal hydrogen transfer is shown to be involved in the formation of the ion at m/z 126 with dimethyloxazoline derivatives and for the ion at m/z 164 with picolinyl esters. Inclusion of a fluorine atom alpha to the carboxyl of a fatty acid has been demonstrated to enhance rearrangements for expulsion of internal chain fragments with both methyl ester and dimethyloxazoline derivatives. When two fluorine atoms are inserted into the alpha position a similar rearrangement has been shown to occur with picolinyl esters, although not nearly to the same extent as that observed with either of the other derivatives. Mechanisms for such rearrangements are proposed and discussed. With fatty acid dimethyloxazoline derivatives the M-15 ion arises solely from the loss of a methyl radical from the ring and the M-43 ion has at least three different mechanisms of formation. Such rearrangements make it difficult to establish the identity of the terminal moiety of the alkyl chain. In mass spectrometry terms the picolinyl ester would seem to be the superior derivative for structural characterisation of fatty acids.

Initial in vitro characterisation of phosphonopyruvate hydrolase, a novel phosphate starvation-independent, carbon-phosphorus bond cleavage enzyme in Burkholderia cepacia Pal6.

A novel, inducible carbon-phosphorus bond cleavage enzyme, phosphonopyruvate hydrolase, was detected in cell-free extracts of Burkholderia cepacia Pal6, an environmental isolate capable of mineralising L-phosphonoalanine as carbon, nitrogen and phosphorus source. The activity was induced only in the presence of phosphonoalanine, did not require phosphate starvation for induction and was uniquely specific for phosphonopyruvate, producing equimolar quantities of pyruvate and inorganic phosphate. The native enzyme had a molecular mass of some 232 kDa and showed activation by metal ions in the order Co2+ > Ni2+ > Mg2+ > Zn2+ > Fe2+ > Cu2+. Temperature and pH optima in crude cell extracts were 50 degrees C and 7.5, respectively, and activity was inhibited by EDTA, phosphite, sulfite, mercaptoethanol and sodium azide. Phosphonopyruvate hydrolase is the third bacterial C-P bond cleavage enzyme reported to date that proceeds via a hydrolytic mechanism.

Effect of beta-adrenoreceptor blockade with nadolol on the duration of local anesthesia.

BACKGROUND: beta-adrenoreceptor blockers, or beta-blockers, are drugs commonly prescribed for hypertension, angina and migraine headaches. In a patient taking beta-blocker medication, administration of a local anesthetic containing a vasoconstrictor could result in an adverse interaction. METHODS: The authors conducted a double-blind, randomized, crossover, placebo-controlled study to test the hypothesis that a nonselective beta-blocker--nadolol--enhances vasoconstriction induced by the epinephrine contained in local anesthetic, thus resulting in an increased duration of anesthesia. Ten healthy male volunteers were given either a placebo or a single, standard oral dose of nadolol (80 milligrams). The upper lateral incisor teeth were anesthetized using lidocaine with or without epinephrine. RESULTS: The mean duration of pulpal and soft-tissue anesthesia was increased in subjects who took nadolol compared with those who took placebo by 17 minutes (58 percent) and 16.5 minutes (19 percent), respectively, when they received 1 milliliter of lidocaine containing 1:100,000 epinephrine. These differences were both clinically and statistically significant (P = .007). Using lidocaine without epinephrine produced no clinically or statistically significant difference in duration of pulpal or soft-tissue anesthesia in the two groups of subjects. The authors noted no significant changes in blood pressure or pulse rate. CONCLUSIONS: Administration of local anesthetic containing epinephrine to subjects receiving a beta-blocker increased the duration of pulpal and soft-tissue anesthesia. There was no difference in duration of anesthesia between groups when local anesthetic without epinephrine was used. CLINICAL IMPLICATIONS: Use of local anesthetic containing a vasoconstrictor should be avoided in patients taking beta-blocker medication because of a possible adverse drug interaction. However, when a vasoconstrictor is indicated for hemostasis, the local anesthetic should be administered slowly and in small amounts as pulse rate and blood pressure are being monitored. The patient should be informed that the duration of anesthesia might be prolonged.

Halomethane:bisulfide/halide ion methyltransferase, an unusual corrinoid enzyme of environmental significance isolated from an aerobic methylotroph using chloromethane as the sole carbon source.

A novel dehalogenating/transhalogenating enzyme, halomethane:bisulfide/halide ion methyltransferase, has been isolated from the facultatively methylotrophic bacterium strain CC495, which uses chloromethane (CH(3)Cl) as the sole carbon source. Purification of the enzyme to homogeneity was achieved in high yield by anion-exchange chromatography and gel filtration. The methyltransferase was composed of a 67-kDa protein with a corrinoid-bound cobalt atom. The purified enzyme was inactive but was activated by preincubation with 5 mM dithiothreitol and 0.5 mM CH(3)Cl; then it catalyzed methyl transfer from CH(3)Cl, CH(3)Br, or CH(3)I to the following acceptor ions (in order of decreasing efficacy): I(-), HS(-), Cl(-), Br(-), NO(2)(-), CN(-), and SCN(-). Spectral analysis indicated that cobalt in the native enzyme existed as cob(II)alamin, which upon activation was reduced to the cob(I)alamin state and then was oxidized to methyl cob(III)alamin. During catalysis, the enzyme shuttles between the methyl cob(III)alamin and cob(I)alamin states, being alternately demethylated by the acceptor ion and remethylated by halomethane. Mechanistically the methyltransferase shows features in common with cobalamin-dependent methionine synthase from Escherichia coli. However, the failure of specific inhibitors of methionine synthase such as propyl iodide, N(2)O, and Hg(2+) to affect the methyltransferase suggests significant differences. During CH(3)Cl degradation by strain CC495, the physiological acceptor ion for the enzyme is probably HS(-), a hypothesis supported by the detection in cell extracts of methanethiol oxidase and formaldehyde dehydrogenase activities which provide a metabolic route to formate. 16S rRNA sequence analysis indicated that strain CC495 clusters with Rhizobium spp. in the alpha subdivision of the Proteobacteria and is closely related to strain IMB-1, a recently isolated CH(3)Br-degrading bacterium (T. L. Connell Hancock, A. M. Costello, M. E. Lidstrom, and R. S. Oremland, Appl. Environ. Microbiol. 64:2899-2905, 1998). The presence of this methyltransferase in bacterial populations in soil and sediments, if widespread, has important environmental implications.

Propofol induces dilation and inhibits constriction in guinea pig basilar arteries.

The present study investigated the direct action of propofol on guinea pig basilar arterial rings and the possible underlying mechanisms. Arterial rings, with and without endothelium, were mounted in an organ bath and connected to an isometric tension recording system. The effects of propofol (0.63-20 micrograms/mL) were compared with those of Intralipid (n = 13) after equilibration and precontraction by 5-hydroxytryptamine (5-HT). In another group (n = 8), after pretreatment with either propofol (5 micrograms/mL) or Intralipid, a contraction by 35 mM KCl was obtained and compared. Another group (n = 12) were incubated in Ca(2+)-free Krebs buffer and after depolarization by 45 mM KCl, a dose-response curve to CaCl2 was obtained to compare the effect of propofol (5 micrograms/mL) and Intralipid on the influx of Ca2+. Finally, in Ca(2+)-free Krebs buffer, the effect of Intralipid or propofol on 5-HT-evoked contractions (n = 6) were assessed. Propofol caused significant dilation with or without endothelium present, inhibited KCl-induced contraction, and significantly lowered the dose-response curve for CaCl2. In Ca(2+)-free Krebs buffer, propofol significantly inhibited 5-HT-evoked contraction, which is dependent on intracellular Ca(2+)-release. In conclusion, propofol inhibited vaso-constriction and induced vasodilation by mechanisms consistent with reduced extracellular calcium influx and suppressed intracellular calcium release.

Inhibition of somatic embryo maturation in Sitka spruce [Picea sitchensis (Bong.) Carr.] by butylated hydroxytoluene, a volatile antioxidant released by parafilm.

Head-space volatiles above embryogenicPicea sitchensis (Bong.) Carr. (Sitka spruce) tissues cultured in glass Petri dishes sealed with Parafilm M or cling-film, were captured on Tenax adsorption traps and analysed by gas chromatography / mass spectrometry. Each sealing system released a single major compound into the head-space; butylated hydroxytoluene from Parafilm M and 2-ethyl-1-hexanol from cling-film. After two weeks sealed under Parafilm M butylated hydroxytoluene accumulated to 1.1 µg g(-1) FW in tissues and subsequent somatic embryo maturation was prevented. When butylated hydroxytoluene was supplied via the head-space (100 µg/250 ml flask) 0.5 µg g(-1) FW accumulated in tissues after two weeks and no somatic embryo maturation occurred. Potentially phytotoxic metabolites of butylated hydroxytoluene included a substituted stilbenequinone, butylated hydroxytoluene quinone methide and butylated hydroxytoluene dimer.

In vitro cerebral vasoactive effects of MK-801.

MK-801, although more consistently neuroprotective in focal ischemia, has had more variable success in the management of global ischemia. This difference could be due to a vasoactive effect that would improve blood flow in focal ischemia but would not be operative in global ischemia. Therefore, a possible direct cerebrovascular effect of MK-801 was investigated in vitro in basilar arteries from 13 dogs and 16 guinea pigs. Two rings were obtained from each animal; in one the endothelium was removed and in the other the endothelium was maintained intact. Each ring was suspended in an organ bath and isometric tension was recorded. After half-maximal contractions with either KCl or 5-hydroxytryptamine, a dose of MK-801 or the same volume of saline was added to the bath. MK-801 concentrations between 0.1 and 1.0 microM had no effect on both canine and guinea pig basilar arteries with or without endothelium whereas concentrations 10-160 microM further contracted the arteries in an endothelium dependent fashion, with the exception of the KCl precontracted endothelium intact canine artery. Higher concentrations of MK-801 tended to dilate the arteries and the dilation was endothelium independent. Thus, MK-801 has dose-dependent cerebral vascular effects and our results may explain some of the conflicting results of MK-801 on CBF.

Propofol differentially attenuates the responses to exogenous and endogenous norepinephrine in the isolated rat femoral artery in vitro.

Propofol causes a decrease in vascular resistance mediated in part by a decrease in sympathetic output. To determine whether attenuation of norepinephrine release from sympathetic perivascular nerve terminals could contribute to decreased vascular resistance, we examined the effects of propofol on the contractile responses to exogenous and endogenous norepinephrine in the rat femoral artery. Endogenous norepinephrine was released from sympathetic nerve terminals using electrical field stimulation. The responses to both exogenous norepinephrine and neurally released norepinephrine were attenuated by propofol in concentrations from 1.0 to 10.0 micrograms/mL. At 50% of maximal and at maximal contractile responses to norepinephrine and electrical field stimulation, the response to electrical field stimulation was inhibited to a greater extent than the response to exogenous norepinephrine. This suggests that, in addition to direct postsynaptic vasodilation, propofol has the presynaptic effect of inhibiting norepinephrine release from perivascular nerves.