C-L-Methionine

This compound is used for the detection of different types of malignancies, reflecting the amino acid utilization (transport, protein synthesis, transmethylation, etc.). 

Raclopride is labeled with nC either by iV-ethylation with [1-UC] iodoethane or by O-methylation with [UC] iodomethane, although the latter is more suitable for routine synthesis. Both 11C-labeled iodoethane and iodomethane are prepared from 11C-C02. The product is purified by HPLC giving a purity of greater than 98%. The specific activity should be in the range of 0.5-2 Ci/Vmol (18.5-74 GBq/Vmol). The product at pH between 4.5 and 8.5 remains stable for more than 1 h at room temperature. The molecular structure of 11C-raclopride is shown in Fig.8.2e. 

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Fermentation of Streptomyces niveus in the presence of Me-[ C]-L-methionine yielded novobiocin with an incorporation of 10 per cent of the added isotope °°. The radioactivity was distributed between the 0-methyl and gem-dimethyl groups of the sugar noviose (66 per cent) and the C-methyl group of the coumarin fragment (123,35 per cent) and thus indicated that the coumarin methyl group was formed by a process of C-methylation. The timing of this step is, however, not known. Enzyme systems have been isolated from Streptomyces niveus which are capable of rapid amide bond formation between the isoprenyl 4-hydroxybenzoic acid (125) and the coumarin (123) to give novobiocic acid. The reaction requires ATP and presumably involves some form of activation of the p-hydroxybenzoyl carboxyl function. 

Methicillin — see Penicillin, 2,6-dimethoxyphenyl-Methidathion insecticidal activity, 6, 576 as insecticide, 1, 196 Methine, dipteridyl-synthesis, 3, 303 Methine dyes, 1, 323-325, 332 L-Methionine, S-adenosyl-in metabolic iV-methylation, 1, 236 Methionine, dehydro- C NMR, 6, 139 X-ray crystallography, 6, 136 Methiothepin... 

Esterification of the propionic acid side chain at C-13 (ring C) with a methyl group catalyzed by S-adenosyl-L-methionine-magnesium protoporphyrin 0-meth-yltransferase yields protoporphyrin IX monomethyl ester (MPE), which originates protochlorophyllide by a P-oxidation and cyclization of the methylated propionic side chain. This molecule contains a fifth isocyclic ring (ring E), the cyclopentanone ring that characterizes aU chlorophylls. 

Griffiths S.W. and Cooney C.L. (2002), Relationship between protein structure and methionine oxidation in recombinant human alpha 1-antitrypsin, Biochemistry 41, 6245-6252. 

In biological methylation, the 5-methyl group of the amino acid L-methionine is used to methylate suitable O, N, S, and C nucleophiles. First, methionine is converted into the methylating agent S-adenosylmethionine (SAM). SAM is nucleoside derivative (see Section 14.3). Both the formation of SAM and the subsequent methylation reactions are nice examples of biological Sn2 reactions. 

Methyltransferases that utilize S-adenosyl-L-methionine as the methyl donor (and thus generating S-adenosyl-L-homocysteine) catalyze (a) A-methylation (e.g., norepinephrine methyltransferase, histamine methyltransferase, glycine methyltransferase, and DNA-(adenine-A ) methyltransferase), (b) O-methylation (e.g., acetylsero-tonin methyltransferase, catechol methyltransferase, and tRNA-(guanosine-0 ) methyltransferase), (c) S-methyl-ation (e.g., thiopurine methyltransferase and methionine S-methyltransferase), (d) C-methylation (eg., DNA-(cy-tosine-5) methyltransferase and indolepyruvate methyltransferase), and even (e) Co(II)-methylation during the course of the reaction catalyzed by methionine syn-thase. ... 

Hydantoinases belong to the E.C.3.5.2 group of cyclic amidases, enzymes that catalyze the hydrolysis of hydantoins 7-11,147). Because synthetic hydantoins are accessible by a variety of chemical syntheses, including Strecker reactions, enan-tioselective hydantoinase-catalyzed hydrolysis offers an attractive and general route to chiral amino acid derivatives. Moreover, because hydantoins are easily racemized chemically or enzymatically by appropriate racemases, dynamic kinetic resolution with potential 100% conversion and complete enantioselectivity is theoretically possible. Indeed, a number of such cases have been reported 147). However, if asymmetric induction is poor or if inversion of enantioselectivity is desired, directed evolution can come to the rescue. Such a case has been reported, specifically in the production of L-methionine as part of a whole cell system E. coll) (Figure 22) 148). 

Enzymatic O-methylation of flavonoids, which is catalyzed by O-methyltransferases (E.C. 2.1.1.6-) involves the transfer of the methyl group of an activated methyl donor, S -adenosyl-L-methionine, to the hydroxyl group of a flavonoid acceptor with the formation of the corresponding methylether and S -adenosyl-L-homocysteine. The latter product is, in... 

Brossi, A. 1991. Mammalian alkaloids Conversion of tetrahydroisoquinoline-1-carboxylic acids derived from Dopamine. Planta Medica, 57 S93-S100 and, Xe, X. S., Tadic, D Brzostowska, M Brossi, A., Bell, M. and Creveling, C. 1991. Mammalian alkaloids - Synthesis and O-methylation of (S)-3 -hydroxycoclaurine and R-3 -hydroxycoclaurine and their N-methylated analogs with S-adenosyl-L-[methyl-C-14]methionine in presence of mammalian catechol O-methyltransferase. Helvetica Chimica Acta, 74 1399-1411. 

Freeman, H. C., and Golomb, M. L. (1970). Model compounds for metal-protein interaction Crystal structure of three platinum(Il) complexes of l- and DL-methionine and glycyl-L-methionine. Chem. Commun. pp. 1523-1524. 

Recent developments on research into a bacterial C-F bond forming enzyme are reviewed. The fluorinase enzyme was isolated from Streptomyces cattleya in 2002 and shown to catalyse the conversion of fluoride ion and S-adenosyl-L-methionine (SAM) to 5 -fluoro-5 -deoxyadenosine (5 -FDA) and L-methionine. Subsequently, the enzyme has been the subject of cloning, crystallisation, mechanism and substrate specificity studies. This review summarises the current status of this research. 

The fluorinase enzyme mediates a substitution reaction whereby fluoride ion displaces L-methionine with formation of a C-F bond and cleavage of a C-S bond. In order to explore the mechanism in detail, the process has been explored both experimentally and theoretically. The stereochemical course of the reaction was of immediate interest, particularly to delineate between direct inversion or double inversion during the substitution process. A direct substitution will proceed with inversion of configuration at the C5 carbon, whereas a double inversion process will proceed with an overall retention of configuration at the C-5 carbon. To explore this, it was important to prepare SAM 8 carrying a stereospecifically... 

Finally, recent developments on research into the first C-F bond forming enzyme are summarized. The fluorinase enzyme isolated from Streptomyces cat-tleya catalyzes the formation of 5 -fluoro-5 -deoxyadenosine from S-adenosyl-L-methionine and fluoride. The substrate specificity and subsequent transformation of the fluorinated nucleoside to fluoroacetic acid and to fluoro threonine are discussed. 

Caballero, F., Fernandez, A., Matias, N., Martinez, L., Fucho, R., Elena, M., Caballeria, J., Morales, A., Fernandez-Checa, J. C., and Garcia-Ruiz, C. (2010). Specific contribution of methionine and choline in nutritional nonalcoholic steatohepatitis Impact on mitochondrial s-adenosyl-l-methionine and GSH. /. Biol. Chem. doi 10.1074/jbc.M109.099333. 

Leong, S. L., Pham, C. L., Galatis, D., Eodero-Tavoletti, M. T., Perez, K., Hill, A. E., Masters, C. L., Ali, F. E., Barnham, K. J., and Cappai, R. (2009). Formation of dopamine-mediated alpha-synuclein-soluble oligomers requires methionine oxidation. Free Radio. Biol Med. 46,1328-1337. 

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