2-Oxovalerate

A ring-chain equilibrium displaced in favor of the cyclic tautomer was observed [78JBC(253)5407 83LA1623] in neutral aqueous solutions of 5-carbamido- 66 n = 3 Xt = 5.67) and 5-guanidino-2-oxovaleric 67 n = 3 Xt = 3.17) acids. In aqueous solutions of acid 67 (w = 3), H-NMR spectroscopy detected the presence of 4% of the open-chain tautomer hydrate 67A (n = 3). In acidic medium, the amount of this hydrate is higher. The dipolar cyclic structure of 67B (n = 3) in the solid state was established on the basis of X-ray diffraction data [83AX(C)1240]. Both isomers 67A and... 

The solution phase synthesis of peptides often results in mixtures of labelled, unlabelled compounds along with other impurities and requires extensive purification. A route using a solid phase approach [polyethylene glycol-poly-styrene PEG-PS derivatised with a xanthen-2-oxovalerate (XAL) linker] was recently developed [193] (Scheme 44). 

In 1941 Gakhokidze40 realized a different type of Grignard synthesis on a carbohydrate acid derivative. Methyl L-ery(liro-3,4,5-trimethoxy-2-oxovalerate (XXXII), was treated with one mole of methylmagnesium iodide to produce methyl 2-methyl-2-hydroxy-L-er /(firo-3,4,5-trimethoxy-valerate (XXXIII). The configuration of the second carbon atom in... 

A soluble alanine aminotransferase considerably purified from tomato fruit tissue (Rech and Crouzet, 1974) did not use aspartate, glycine, threonine, leucine, methionine, arginine, or phenylalanine as amino donors glyoxylate and 2-oxovalerate were not used as amino acceptors. Mitochondria from tomato fruit yielded what was apparently the same protein (Gazeu-Reyjal and Crouzet, 1976). The mitochondrial enzyme did not utilize threonine, methionine, aromatic or branched-chain amino acids. 

NH3-gas passed at room temp, into a ca. 20 -soln. of 4,4-dimethyl-2-oxovaleric acid thioamide and cyclohexanone in methanol until the orange soln. turns yellow, and allowed to stand 10 min. 2,2-pentamethylene-4-neopentyl-J -imidazoline-5-thione. Y 89. F. e. s. F. Asinger and F. Gentz, M. 96, 1474 (1965). 

Fig. 6.5 Biosynthesis of bianched-chain capsaicinoids starting with a branched amino acid, e.g., L-valine — 2-oxovalerate —> isobutyryl CoA —> elongation (-t 3 x malonyl CoA) —> [- 3 x COj] — (activated) 8-methylnonanoicacid+vanillylamine—>dihydiocapsaicin[R=(Cllj) CH(CH3)CHj] CS = capsaicin(oid) synthase...

Methyl-2-oxopentanoate =iL-leucine 3-Methyl-2-oxobutanoate =iL-valine 3-Methyl-2-oxovalerate =iL-isoleucine ) Branched-chain-amino-acid aminotransferase L-Glutamate... 

Methyl-2-oxobutanoate L-valine Valine-3-methyl-2-oxovalerate aminotransferase L-lsoleucine... 

Fig. 4.4 Chromatograin of O-trimethylsilylquinoxalinols of standard 2-oxo acids separated on 3 per cent OV-1 on Gas Chrom Q (100-120 mesh) using temperature programming from SO C to 180°C at 2 C min". Peak identifications are 1, pyruvate 2, 2-oxobutyrate 3, 2-oxoisovalerate 4, 2-oxovalerate 5, 2-oxo-3-methylvalerate 6, 2-oxoisocaproate 7, 2-oxo-octanoate 8, 2-oxo-4-methylthiobutyrate 9, 2-oxo-glutarate 10, phenylpyruvate 11,2-oxoadipate. (Redrawn with modifications from Langenbeck et ai. 1975)...

Although these derivatives are limited to 2-oxocarboxylic acids, their mass spectra give rise to several ions which are common to most of the compounds in the series and permit their detection by SIM (Langenbeck etal., 1977a). The mass spectrum of the trimethylsilylated quinoxalinol formed from 2-oxovaleric acid is shown in Fig. 5.19. 

Fig. 5.19 Mass spectrum of the trimethylsilyl derivative of the quinoxalinol of 2-oxovaleric acid.

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