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.

Ineffectiveness of beta-adrenergic blockers on ventilatory response to carbon dioxide.

The effects of the beta-adrenoceptor blockers atenolol, metoprolol, pindolol, and propranolol on the ventilatory response to carbon dioxide rebreathing have been determined in a double-blind randomized manner. Eight healthy, male, nonsmoking subjects received cumulative doses of each drug over a 10-hr period. The effects of each drug on heart rate and carbon dioxide sensitivity were determined at intervals of 2 hr and were related to plasma concentrations of each drug. Maximum reduction of exercise heart rate was achieved with all four beta blockers and plasma concentrations were in the usual therapeutic range for these drugs. There was considerable intersubject and within-subject variability in ventilatory responsiveness to inhaled carbon dioxide, but we were not able to discern any alteration in central sensitivity to increasing carbon dioxide concentrations.

Effect of hypoxia on responses of respiratory smooth muscle to histamine and LTD4.

The aim of the present study was to compare the effect of reduced oxygenation on the contractions of pulmonary vascular and airway smooth muscle induced by leukotriene D4 (LTD4) with those induced by histamine (an agonist with similar mechanisms of smooth muscle contraction) and KCl (a voltage-dependent stimulus). During hypoxia (PO2: 40 +/- 4 Torr) the responses of isolated porcine pulmonary artery and vein spiral strips to LTD4 increased approximately three- and two-fold, respectively, and the vein also exhibited an augmented response to histamine. The augmentation was blunted (LTD4) or reversed (histamine) during anoxia (PO2: 0 +/- 2 Torr). Responses to KCl were not systematically altered by reduced oxygenation. In contrast, the contractions of the guinea pig parenchymal lung strip by all three agonists were generally suppressed by reduced oxygenation. After reoxygenation, the contractile responses of each of the three smooth muscle preparations were generally increased compared with previous and concurrent base-line observations, particularly the LTD4-induced pulmonary vein contraction that increased approximately sevenfold after reoxygenation after anoxia. The contribution (if any) of leukotrienes to hypoxic pulmonary vasoconstriction may reflect increased vascular responsiveness to leukotrienes during hypoxia as well as (or instead of) increased leukotriene release.

Responses of isolated guinea pig pulmonary venules to hypoxia and anoxia.

Because small pulmonary arteries are believed to be the major site of hypoxic pulmonary vasoconstriction (HPV), pulmonary venular responses to hypoxia have received little attention. Therefore the responses of isolated guinea pig pulmonary venules to hypoxia (bath PO2, 25 Torr) and anoxia (bath PO2, 0 Torr) were characterized. Pulmonary venules [effective lumen radius (ELR), 116 +/- 2 microns] with an adherent layer of parenchyma responded to hypoxia and anoxia with a graded sustained contraction (hypoxia, 0.03 +/- 0.01; anoxia, 0.26 +/- 0.03 mN/mm), whereas paired femoral venules (ELR, 184 +/- 7 microns) contracted to anoxia only (0.05 +/- 0.02 mN/mm). Repeated challenges with hypoxia and anoxia continued to elicit sustained pulmonary venular contractions; femoral venule contractions to anoxia were not repeatable. Hypoxia- and anoxia-induced pulmonary venular contractions were calcium and pH dependent. Dissection of the parenchyma from pulmonary venules did not alter contractions to decreased PO2. Anoxic contractions of pulmonary venules were variably reduced by replacement of the bath fluid; however, the release of a contractile mediator(s) from pulmonary venules during hypoxia or anoxia was not demonstrated. Pulmonary venular responses to hypoxia and anoxia are similar to those induced by hypoxia in vivo, and results obtained from this model may be useful in predicting mechanisms of HPV.

Studies of the action of nicotine in guinea-pig tracheal smooth muscle: interaction with beta-adrenoceptor antagonists.

Nicotine produced cholinergic excitatory and adrenergic and non-adrenergic inhibitory responses in isolated guinea-pig trachea. Responses were blocked by hexamethonium (10 micro M), lidocaine (85 micro M) or tetrodotoxin (0.01 micro M) demonstrating that nicotinic receptors in nervous tissue were being activated. In the presence of atropine (0.1 micro M), inhibitory responses to nicotine were partially blocked by specific, experimentally determined, beta-blocking concentrations of pindolol or sotalol or by pretreatment with 6-hydroxydopamine or reserpine but were completely blocked by the less specific beta-blocking drugs 1- and dl-propranolol. Parallel experiments on guinea pig ileum revealed a marked attenuation by dl-propranolol of the atropine sensitive, cholinergic excitatory response to applied nicotine. The non-beta-adrenoceptor blocking agent d-propranolol, produced qualitatively similar attenuation of all excitatory and inhibitory responses to nicotine on both preparations. The remarkable susceptibility of nicotine-induced, neurally mediated responses to low, beta-blocking concentrations of dl-propranolol and to low concentrations of both of its racemates suggests that the non-specific actions of these compounds may have much more significance than is customarily believed. Such studies on the interaction between nicotine and some beta-adrenoceptor blocking drugs are consistent with the hypothesis that non-beta-blocking so-called 'non-specific membrane depressant actions' of dl-propranolol may in concentrations previously considered 'sub-local anaesthetic', significantly depress physiological transmission induced by activation of nicotinic receptors.

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.

An open label trial of the possible analgesic effects of dipyridamole.

There is experimental evidence that adenosine and the adenosinergic agent dipyridamole may inhibit the activity of nociceptive neurons. Dipyridamole was given to 15 patients with chronic pain in an open uncontrolled investigation. Eleven patients tolerated the drug well and seven of these patients obtained subjective benefit. The results are held to justify further investigation under controlled blind conditions. A possible ceiling effect of dipyridamole was noted.

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.

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.

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.

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.

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.