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1987 9 685 690 Para, G. M., Lucciardi, P., Baratti, J. C.: Synthesis of L-tyrosine by immobilized Escherichia

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Abstract  

A modified method for the preparation of L-[131/123I] iodotyrosine as a brain imaging agent is described. The method is based on direct electrophilic radioiodination of L-tyrosine with NaI [131/123I] using chloramine-T (CAT) and 0.001 g KI as a carrier at pH 7.0. The product was purified by reverse phase high performance liquid chromatography (HPLC). A high radiochemical yield up to 85% of L-[131/123I] iodotyrosine has been achieved with radiochemical purity of greater than 97%. The relation between the pKa of L-tyrosine and pH of the reaction medium was calculated in order to correlate the radiochemical yield of L-[131/123I] iodotyrosine and the state of the three ionizable groups of L-tyrosine. Also, the influence of the reaction conditions on the radiochemical yield of L-[131/123I] iodotyrosine was investigated.

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Cerebral amino acid metabolism is known to be associated with various psychosomatic disorders. 3-(123I)iodo-L-alpha methyl tyrosine (123I-L-AMT) is an alternative to the PET radiopharmaceutical, 11C- thymidine, for brain SPECT studies. Radioiodination of L-alphamethyl tyrosine using chloramine T as well as iodogen has been standardized using 125I as the first step towards the development of the SPECT imaging agent 123I-L-AMT. Purification of the iodinated product was carried out over Sephadex LH-20 column. A quick and easy purification method using Sep-pak column also has been standardized. Quality control of the 125I-L-AMT was carried out by estimating the radiochemical purity and stability of the product. Biodistribution studies of the product were carried out in mice. Time dependent pharmacokinetic studies and activity distribution pattern in the different parts of the brain were also carried out.

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Oscillatory Transenantiomerization of l -Tyrosine, J. Liq. Chromatogr. Related Technol., 2008 (in press). Virtual catalog of ScienceLab.com ( http://sciencelab.com/ ) R

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A radiometric recoil130Im+130I atom tracer technique was developed for determining iodide ionbiomolecule association in liquid and frozen aqueous solutions of slightly soluble biomolecule solutes. It was found that the iodide ion associates with 5-iodouracil and 3-iodo-L-tyrosine, but exhibits no association with uracil and 3,5-diiodo-L-tyrosine.

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The observed rate constant ratio,k 1obs/k 2 obs, for the sequential iodination of L-tyrosine was determined in the concentration range 1.84·10–3 to 1·10–6 M by the use of3H- and14C-labels and product analysis by HPLC. Iodinations by chloramine-T/I gave (k 1 obs/k 2 obs)· values (=the pH dependent factor) in the range 72±3 to 55±2 and molecular iodine iodinations gave values in the range 64±5 to 39±10. It is concluded that molecular iodine is the iodinating species in both cases.

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Triphenyltin(IV) complexes ofN-acetylglycine,N-acetyl-L-leucine,N-acetyl-L-asparagine andN-acetyl-L-tyrosine were prepared by two methods and characterized by means of different spectroscopic methods (FTIR, multinuclear,1H,13C and119Sn NMR and119Sn Mössbauer). The spectroscopic data indicated that theN-acetylglycine complex adopts a trigonal-bipyramidal structure in which the monodentate carboxylate and the amide-C=O group are bound to the same organotin(IV) moiety. The other three complexes are linear oligomers in which the planar Ph3Sn(IV) is coordinated axially by a monodentate carboxylate and an amide-C=O from two different ligands. At theC-terminal end of the oligomer chain there is a tetracoordinated tin(IV) with a monodentate carboxylate as donor group.

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Isothermal calorimetry and UV-visible spectrophotometry have been used to study the thermochemistry of the enzyme-catalyzed hydrolysis of hydrophobic L-amino acid esters in organic solvents with low water content at 298 K. The p-nitrophenyl esters of Z-L-tyrosine and Z-L-phenylalanine were used as model hydrophobic substrates. Acetonitrile was used as a model organic solvent. A special preparation protocol of the reactants in the calorimetric vessel was applied in order to determine the heat effects accompanying the enzyme-catalyzed hydrolysis reaction in organic mixtures with low water content and the Tris buffer ionization enthalpies over the whole range of water content in acetonitrile. It was found that the molar enthalpy of the hydrolysis of p-nitrophenyl esters and buffer ionization enthalpy depend significantly and similarly on the water content in acetonitrile. However, the reaction enthalpy corrected for the buffer ionization enthalpy does not depend on the water content in organic solvent mixtures. An explanation of the effect of the selected organic solvent on the thermochemical parameters was provided on the basis of the IR spectroscopic data for the hydrogen bond network of water in acetonitrile. The results obtained show that the state of water in organic solvents is an important factor that determines the reaction enthalpy as well as buffer ionization enthalpy.

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