4- Hydroxyphenylpyruvate

The liquid is transferred to a continuous extractor (Note 10) and extracted with ether until the supernatant layer of ether remains colorless (about 2 hours). The ethereal extract is discarded (Note 11). The aqueous solution is transferred to a 1-1. beaker and acidified by the cautious addition of 60 ml. of 121V hydrochloric acid (Note 12). The solution is returned to the extractor, which is attached to a tared round-bottomed flask. The solution is extracted with ether until no more -hydroxyphenylpyruvic acid is obtained (Note 13). The undried ether solution is evaporated to dryness on a boiling water bath to give crude p-hydroxy-phenylpyruvic acid as a pale-yellow crystalline mass. The mass is broken up with a spatula, and the flask is kept over potassium hydroxide in a vacuum desiccator until its weight is constant. The yield of crude acid is 6.9-7.2 g. (92-96%). It melts at 210— 215° (dec.) (Note 14). 

Hydroxyphenylpyruvic acid is rapidly oxidized in alkaline solution. Commercially available compressed nitrogen may be used if the gas is further purified by passage through an alkaline solution of pyrogallol (45 g. of pyrogallol dissolved in 300 ml. of 50% sodium hydroxide solution). 

Hydroxyphenylpyruvic acid has been prepared by alkaline hydrolysis of the azlactone of a-benzoylamino- -acetoxycin-namic acid 7 and by a two-step hydrolysis of the azlactone of a-acetamino- -acetoxycinnamic acid.8 p-Hydroxyphenylpyruvic acid has also been prepared by alkaline hydrolysis of 5-( -hy-droxybenzal)-3-phenylhydantoin.9 The procedure described here is adapted from published directions for the preparation of -hydroxyphenylpyruvic-3-C14 acid.5 5-( -Hydroxybenzal)hy-dantoin is prepared according to the method of Boyd and Robson.10... 

Hydroxyphenylpyruvic acid plays an important role in the biogenesis of compounds with a phenylpropane skeleton, and it has been used as substrate in several enzyme studies. Published procedures for its preparation are unsatisfactory in many ways. The alkaline hydrolysis of the azlactone of a-bcnzoylamino- -acetoxycinnamic acid 7 makes necessary a tedious separation of the resulting benzoic acid, and the yield is only 34% based on -hydroxybenzaldehyde. The hydrolysis of 5- ( -hydroxybenzal)-3-phenylhydantoin 9 requires a separation of phenylurea. Finally, the two-step cleavage of the azlactone of a-acetamino- -acetoxycinnamic acid 8 does not proceed easily, and impure products are obtained. In applying this procedure to the synthesis of a carboxyl-labeled -hydroxyphenylpyruvic acid, the overall yield was only 9%.u It must be kept in mind that any prolonged isolation procedure will cause some decomposition of this sensitive compound. 

The probable metabohc defect in type I tyrosine-mia (tyrosinosis) is at himarylacetoacetate hydrolase (reaction 4, Figure 30-12). Therapy employs a diet low in tyrosine and phenylalanine. Untreated acute and chronic tyrosinosis leads to death from liver failure. Alternate metabolites of tyrosine are also excreted in type II tyrosinemia (Richner-Hanhart syndrome), a defect in tyrosine aminotransferase (reaction 1, Figure 30-12), and in neonatal tyrosinemia, due to lowered y>-hydroxyphenylpyruvate hydroxylase activity (reaction 2, Figure 30-12). Therapy employs a diet low in protein. 

SCHULZ A, CRT o, BEYER P and KLEINIG H (1993) SC-0051, a 2-benzoyl-cyclohexane-l,3-dione bleaching herbicide, is a potent inhibitor of the enzyme /<-hydroxyphenylpyruvate dioxygenase , Terr, 318, 162-6. 

Lindblad B, G Lindstedt, S Lindsted (1970) The mechanism of enzymatic formation of homogentisate from / -hydroxyphenylpyruvate. J Am Chem Soc 92 7446-7449. 

Lindstedt S, B Odelhbg, M Rundgren (1977) Purification and properties of 4-hydroxyphenylpyruvate dioxygenase from Pseudomonas sp. P. J. 874. Biochemistry 16 3369-3377. 

Ruetschi U, B Odelhdg, S Lindstedt, J Barros-Soderling, B Persson, H Jornvall (1992) Characterization of 4-hydroxyphenylpyruvate dioxygenase. Primary structure of the Pseudomonas enzyme. EurJ Biochem 205 459-466. 

Pseudomonas sp. strain P.J. 874 grown with tyrosine carried out dioxygenation of 4-hydroxyphenylpyruvate to 2,5-dihydroxyphenylacetate accompanied by an NIH shift (Lindstedt et al. 1977). The involvement of a high-spin ferric center coordinated with tyrosine is conclusively revealed in the primary structure of the enzyme (Riietschi et al. 1992). 

The anodic oxidation of methyl-3,5-dibromo-4-hydroxyphenylpyruvate oxime affords a spiroisooxazole in almost quantitative yield (Scheme 27) [38]. 

Yang DY. (2003) 4-Hydroxyphenylpyruvate dioxygenase as a drug discovery target. Drug News Perspect 16 493 96. 

The liver is also the principal metabolic center for hydrophobic amino acids, and hence changes in plasma concentrations or metabolism of these molecules is a good measure of the functional capacity of the liver. Two of the commonly used aromatic amino acids are phenylalanine and tyrosine, which are primarily metabolized by cytosolic enzymes in the liver [1,114-117]. Hydroxylation of phenylalanine to tyrosine by phenylalanine hydroxylase is very efficient by the liver first pass effect. In normal functioning liver, conversion of tyrosine to 4-hy-droxyphenylpyruvate by tyrosine transaminase and subsequent biotransformation to homogentisic acidby 4-hydroxyphenylpyruvic acid dioxygenase liberates CO2 from the C-1 position of the parent amino acid (Fig. 5) [1,118]. Thus, the C-1 position of phenylalanine or tyrosine is typically labeled with and the expired C02 is proportional to the metabolic activity of liver cytosolic enzymes, which corresponds to functional hepatic reserve. Oral or intravenous administration of the amino acids is possible [115]. This method is amenable to the continuous hepatic function measurement approach by monitoring changes in the spectral properties of tyrosine pre- and post-administration of the marker. 

Leptospermone (34), a representative of an important new class of herbicides from the bottlebrush plant, Callistemon citrinus (Curtis) Skeels, has been found to have an inhibitory effect on the enzyme, -hydroxyphenylpyruvate dioxygenase (HPPD), involved in the synthesis of plastoquinone in plants. Nitisinone (35), a synthetic derivative of (34), has recently been introduced to the market for the treatment of hereditary tyrosinemia type 1 (HT-1), a severe genetic disease caused by a deficiency of fumaryl acetoacetate hydrolase (FAH). ... 

The molecular target site of triketone herbicides is the enzyme -hydroxyphenylpyruvate dioxygenase (HPPD). Inhibition of this enzyme disrupts the biosynthesis of carotenoids and causes a bleaching (loss of chlorophyll) effect on the foliage similar to that observed with inhibitors ofphytoene desaturase (e.g. norflurazon). However, the mechanism of action of HPPD inhibitors is different. Inhibtion of HPPD stops the synthesis of homogen tisate (HGA), which is a key precursor of the 8 different tocochromanols (tocopherols and tocotrienols) and prenyl quinones. In the absence of prenylquinone plastoquinone, phytoene desaturase activity is interrupted. The bleaching of the green tissues ensues as if these compounds inhibited phytoene desaturase. 

Lee DL, PrisbyUaMP, CromartieTH, Dagarin DP, Howard SW, Provan WM, EUis MK, Fraser T, Mutter LC, The discovery and structural requirements of inhibitors of hydroxyphenylpyruvate dioxygenase. Weed Sci 45 601—609,... 

Meazza G, Scheffler BE, Tellez MR, Rimando AM, Nanayakkara NPD, Khan LA, Abourashed EA, Romagni JG, Duke SO, Dayan EE, The inhibitory activity of natural products on plant -hydroxyphenylpyruvate dioxygenase. Phytochemistry 59 281-288, 2002. 

Dayan EE, Duke SO, Sauldubois A, Singh N, McCurdy C, Cantrell CL, -Hydroxyphenylpyruvate dioxygenase is a target site for P-triketones from Lep-tospermum scoparium Phytochemistry, 2007. 

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