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High Specific Activity (high + specific_activity)
Selected AbstractsIschaemic preconditioning is related to decreasing levels of extracellular adenosine that may be metabolically useful in the at-risk myocardium: an experimental study in the pigACTA PHYSIOLOGICA, Issue 1 2010A. Waldenström Abstract Aim:, ,Pre-treatment' with short repetitive periods of ischaemia (ischaemic preconditioning) has proved to be a powerful mechanism for modification of the extent of myocardial damage following acute coronary artery occlusion. The exact mechanism of protection induced by ischaemic preconditioning is not known. We herewith put forward a contributing component for protection with preconditioning involving a shift in the adenylate kinase (AK) equilibrium reaction in favour of adenosine triphosphate (ATP) formation. Methods:, A coronary artery was occluded in anaesthetized thoracotomized pigs to induce ischaemic preconditioning as well as a longer period of ischaemia. Microdialysis probes were inserted in ischaemic and control myocardium and were infused with 14C- adenosine with two different specific activities. 14C-lactate was identified and measured in the effluent. Results:,14C-adenosine was taken up by non-preconditioned and preconditioned myocardium during ischaemia. Significantly increased levels of 14C-lactate were recovered in preconditioned myocardium. 14C-adenosine with high specific activity resulted in a specific activity of lactate that was 2.7 times higher than that of lactate after administration of 14C-adenosine with low specific activity. Mass spectrography verified the identity of 14C-lactate. Conclusions:, Preconditioning up-regulates a new metabolic pathway (starting with 5,-nucleotidase and ending up with lactate) resulting in ATP formation in the micromolar range on top of another effect terminating in a useful shift in the AK equilibrium reaction in favour of ATP generation in the millimolar range. Although the up-regulation of the purine nucleoside phosphorylase pathway is clearly demonstrated, its biological relevance remains to be proved. [source] Withania somnifera (Ashwagandha): a Novel Source of L-asparaginaseJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2009Vishal P. Oza Abstract Different parts of plant species belonging to Solanaceae and Fabaceae families were screened for L-asparaginase enzyme (E.C.3.5.1.1.). Among 34 plant species screened for L-asparaginase enzyme, Withania somnifera L. was identified as a potential source of the enzyme on the basis of high specific activity of the enzyme. The enzyme was purified and characterized from W. somnifera, a popular medicinal plant in South East Asia and Southern Europe. Purification was carried out by a combination of protein precipitation with ammonium sulfate as well as Sephadex-gel filtration. The purified enzyme is a homodimer, with a molecular mass of 72 ± 0.5 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresisand size exclusion chromatography. The enzyme has a pH optimum of 8.5 and an optimum temperature of 37 °C. The Km value for the enzyme is 6.1 × 10,2 mmol/L. This is the first report for L-asparaginase from W. somnifera, a traditionally used Indian medicinal plant. [source] Carbon-14 radiosynthesis of combretastatin A-1 (CA1) and its corresponding phosphate prodrug (CA1P)JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 14 2009Rodney T. Brown Abstract The natural product combretastatin A-1 (CA1) is isolated from the African bush willow tree, a member of the Combretaceae family. CA1 has important medicinal value, due in part to its ability to inhibit tubulin assembly. The prodrug combretastatin A-1 diphosphate (CA1P; OXi4503) is currently in human Phase I clinical trials as a vascular disrupting agent. This paper describes the carbon-14 radiosynthesis of [4,- 14C]CA1 and the corresponding phosphate prodrug salt [4,- 14C]CA1P in high specific activity (55,mCi/mmol). The carbon-14 label was introduced by methylation of the C-4, protected phenolic moiety of the CA1 precursor following removal of the tert -butyldimethylsilyl protecting group in the presence of [14C]methyl iodide. This was accomplished in excellent yield without significant Z to E isomerization. The [14C]-precursor ((Z)-1-[3,,[4,- 14C],5,-trimethoxyphenyl]-2-[2,,3,-di-[(isopropyl)oxy]-4,-methoxyphenyl] ethene) was subjected to a de- isopropylation reaction with TiCl4. The tetrabenzyl phosphate derivative of the resulting diol was prepared using fresh dibenzyl phosphite. Debenzylation with trimethylsilylbromide, followed by hydrolysis of the trimethylsilyl ester and adjustment of the pH with dilute aqueous hydrochloric acid yielded [4,- 14C]CA1P with an overall radiochemical yield of 8.4%. Copyright © 2009 John Wiley & Sons, Ltd. [source] Radiosynthesis of novel 18F-labelled derivatives of indiplon as potential GABAA receptor imaging tracers for PETJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 3 2008Steffen Fischer Abstract The involvement of gamma amino butyric acid (GABA) receptors in a variety of neurological and psychiatric diseases has promoted the development and use of radiolabelled benzodiazepines (BZ) for brain imaging by PET. However, these radioligands are unable to distinguish between the various subtypes of GABAA receptors. Novel non-BZ such as the pyrazolo-pyrimidine indiplon proved to be selective for the ,1 -subunit of the GABAA receptor. Here, we describe the syntheses of four novel 18F-labelled indiplon derivatives. Radiosyntheses were performed via n.c.a. 18F-nucleophilic substitution starting from the tosyl, bromo, and 4-nitrobenzoyl precursors to obtain fluorine substituted N -alkylamide side chain derivatives of indiplon, followed by multistep purification using semi-preparative high-performance liquid chromatography and solid phase extraction. Tosyl and bromo precursors were converted into 18F-labelled indiplon derivatives with good and reproducible radiochemical yield (RCY) (35,70%, decay corrected), high radiochemical purity (,98.5%), and high specific activity (,>,150,GBq/µmol). By contrast, a low RCY (5,10%) and specific activity (10,15,GBq/µmol) were achieved for the 4-nitrobenzoyl precursor. Copyright © 2008 John Wiley & Sons, Ltd. [source] Practical [14C]-synthesis of molecules containing an acetic acid moiety: application to [14C]-labeled DP1 antagonistsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 1 2007Carl Berthelette Abstract Efficient carbon-14 labeling of four potent and selective DP1 antagonists is reported. The synthetic sequence began with ,-hydroxylation, reduction of an ester, followed by oxidative diol cleavage and aldehyde reduction. The resulting alcohol 4 was converted to a mesylate then nucleophilic substitution with [14C]-sodium cyanide was performed to yield a nitrile, which upon basic hydrolysis provided the carbon-14 labeled acid 1. Compound 2 was obtained from the same alcohol intermediate 4 and two diastereomeric compounds 6 and 7 were easily prepared from compound 2. Carbon-14 synthesis of compounds 1, 2, 6 and 7 were achieved in good yields, high radiochemical purity (>99%) and with high specific activity (45 mCi/mmol). Copyright © 2006 John Wiley & Sons, Ltd. [source] Carbon-14 labelling of selective H3 receptor antagonistsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 14 2005Steen K. Johansen Abstract The fast and efficient carbon-14 labelling of the three potent H3 antagonists NNC 38-1202, NNC 38-1384, and NNC 38-1401 is reported. The two-step synthetic sequence, which included a Knoevenagel reaction, provided the carbon-14-labelled compounds in 38,55% overall yield starting from [2- 14C]malonic acid. The compounds were all obtained in high radiochemical purity ( > 99%) and with high specific activity (55.8 mCi/mmol). Copyright © 2005 John Wiley & Sons, Ltd. [source] Tritiation of CEP-1347 at high specific activity using several methodsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 5 2005Judith A. Egan Abstract [Thiomethylenes- 3H] CEP-1347 (5) was synthesized by the tritiation of diformyl precursor 3 with NaB3H4 followed by treatment with ethanethiol. [Methyl ester- 3H] CEP-1347 (7) was prepared at even higher specific activity by the alkylation of precursor 6 with C3H3I. Copyright © 2005 John Wiley & Sons, Ltd. [source] A combined loop-SPE method for the automated preparation of [11C]doxepinJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 4 2002R. Iwata Abstract A simple and versatile loop-solid phase extraction (SPE) method was developed for the automated preparation of [11C]doxepin, a histamine H1 receptor antagonist, from [11C]methyl triflate ([11C]MeOTf). This labeling agent was passed through a Teflon or Tefzel loop coated internally with a film of the precursor solution. The reaction products were then flushed from the loop to a short SPE column, where they were concentrated and then injected onto a semi-preparative HPLC column simply by switching an injection valve. By applying this combined loop-SPE technique the whole procedure turned out to be easily automated. The formation of [11C]methylated doxepin ([11C]methyldoxepin) was observed and the ratio of doxepin to methyldoxepin was found to be clearly correlated with the mass ratio of nordoxepin to MeOTf. This observation highlights the importance of [11C]MeOTf specific activity in the [11C]methylation of secondary amines. Using this method, [11C]Doxepin was prepared in over 40% radiochemical yield from high specific activity [11C]MeOTf. Copyright © 2002 John Wiley & Sons, Ltd. [source] Synthesis and characterization of 4,6-dichloroindole-based radioligands for imaging the glycine site of the NMDA ion channelJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 2 2002R. N. Waterhouse Abstract To provide effective PET or SPECT ligands for the glycine binding site of the NMDA ion channel, we have synthesized and characterized in vitro four substituted derivatives of the potent glycine site antagonist 3-[2-[(phenylamino)carbonyl]ethenyl]-4,6-dichloroindole-2-carboxylic acid (Ki=3.0 nM). These new ligands contain groups amenable to labeling with C-11 for PET, or I-123 for SPECT. In vitro analysis of these compounds revealed that placement of a methoxy group at either the ortho or para position of the phenylaminocarbonyl group significantly reduced receptor affinity (Ki=74.0±8.1 and 26.5±4.9 nM, respectively), as did placement of an iodine at the para position (Ki=60.4±8.2 nM). However, the meta -methoxy derivative (4b) maintained high affinity (Ki=4.8±0.9 nM) for the glycine site and was therefore labeled with carbon-11 by reacting the corresponding desmethyl derivative with [11C]methyl iodide. Radiochemical yields of 14±10% (EOS), and high specific activity (1.2±0.5 Ci/,mol (EOS, n=7)) were realized, and the product was prepared in a sterile saline solution suitable for in vivo use. Copyright © 2002 John Wiley & Sons, Ltd. [source] Synthesis of deoxyadenosine-5,-(35S)-thiomonophosphate [dAMP(35S)] of high specific activity , a key intermediate for the synthesis of Sp-deoxyadenosine-5,-(alpha; - 35S)-thiotriphosphate [Sp-dATP (, - 35S)]JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 1 2002K. M. Mathew Abstract Unprotected deoxyadenosine 1 was treated with an excess of phosphorus acid and stoichiometric proportions of N, N,-di- p -tolylcarbodiimide in anhydrous pyridine to give deoxyadenosine-5,-monophosphite 2. The latter was activated with trimethylsilyl chloride followed by sulphurisation with elemental 35S (specific activity>1000 Ci/mmol) in toluene solution to give deoxyadenosine-5,-(35S)-thiomonophosphate [dAMP(35S)] 3. Enzymatic conversion of deoxyadenosine-5,-(35S)-thiomonophosphate to Sp-deoxyadenosine-5,-(, - 35S)-thiotriphosphate [Sp-dATP (, - 35S)] 5 was carried out following a standard reaction protocol. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synthesis and characterization of [phenyl- 3H] clonidine hydrochloride at high specific activityJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 5 2001Crist N. Filer Abstract p-Aminoclonidine hydrochloride 1 was converted to m-dibromo-p-iodoclonidine 3 and the latter was used as a precursor to prepare [phenyl- 3H] clonidine hydrochloride 4 at high specific activity via a selective catalytic dehalogenation with tritium. Copyright © 2001 John Wiley & Sons, Ltd. [source] Crystallization and preliminary crystallographic analysis of thermophilic cellulase from Fervidobacterium nodosum Rt17-B1ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Baisong Zheng FnCel5A, a thermostable endoglucanase, is a member of glycohydrolase family 5 which catalyzes the hydrolysis of cellulose to glucose in the thermophilic bacterium Fervidobacterium nodosum Rt17-B1. FnCel5A is particularly interesting because of its high thermostability (Topt = 353,K, half-life 48,h) and its high specific activity towards carboxymethylcellulose. These properties make FnCel5A an attractive target for protein engineering to improve cellulase activity. In order to resolve the crystal structure of FnCel5A and to gain a better understanding of its biological function, recombinant FnCel5A was expressed, purified and crystallized at 291,K using NaH2PO4/KH2PO4 as a precipitant. A 2.4,Å resolution native data set was collected from a single flash-cooled crystal (100,K) using 20%(v/v) glycerol as a cryoprotectant. These crystals belonged to space group P21212, with unit-cell parameters a = 53.5, b = 81.7, c = 85.2,Å, , = , = , = 90°. One molecule is assumed to be present per asymmetric unit, which gives a Matthews coefficient of 2.5,Å3,Da,1. A data set was also collected to 1.7,Å resolution from a selenomethionyl derivative; it belonged to space group P212121 with the same unit-cell parameters as the native crystals. [source] Bioactive proteins from stonefish venomCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 9 2002Hoon Eng Khoo Summary 1.,Of all the venomous fish known, the stonefish is one of the most commonly encountered by man. Studies on its venom started in the 1950s, but little work was performed after that until several groups revived interest in the venom in the 1980s after easier accessibility to the fish. 2.,Stonefish venom is a mixture of proteins, containing several enzymes, including hyaluronidase of high specific activity. A purified stonefish hyaluronidase has been characterized. 3.,Several of the effects of the crude venom have been isolated to a protein lethal factor that has cytolytic, neurotoxic and hypotensive activity. This protein is stonustoxin from Synanceja horrida, trachynilysin from Synanceja trachynis and verrucotoxin from Synanceja verrucosa. 4.,The biochemical properties and activities of these protein lethal factors are reviewed. [source] | |||||||||||||