Kynurenic acid

The kynurenine pathway metabolites are kynurenine, kynurenic acid, xahthurenic acid, 3-hydroxykynurenine, anthranilic acid and quinolinic acid. The more important are kynurenine (Kyn) and 3-hydroxykynurenine (30HKyn) (Fig 1). 

Kyanisierung, /. kyanizing, kyanization. Kyaphenin, n. cyaphenine, kyaphenine. Kjrnurensaure, /. kynurenic acid. 

Taniuchi H, O Hayaishi (1963) Studies on the metabolism of kynurenic acid. III. Enzymatic formation of 7,8-dihydroxykynurenic acid from kynurenic acid. J Biol Chem 238 283-293. 

The analysis of amino acids involves chromatographic issues similar to those encountered in analysis of simple amines. Underivatized amino acids have, with a few exceptions, weak UV absorbance and a strong tendency to interact with stationary phases in undesirable ways. Underivatized amino acids are normally separated with ion exchange chromatography, then visualized post-column by reaction with ninhydrin, o-phthaladehyde (OPA), or other agents. Underivatized tryptophan and the metabolites kynurenine, 3-hydroxykynurenine, kynurenic acid, and 3-hydroxyanthranilic acid, were separated on a Partisphere 5-p ODS column with fluorescent detection.121... 

Purines such as xanthine (91), hypoxanthine (92), guanine (93), and uric acid (95) are found in excreta of many insects (Table VI) 48). Uric acid (95) is known to be the main end product of nitrogen metabolism in almost all insects. Various purines are found in the wasp Vespa) and the sawfly Gilpinia) in common with other insects (Table VI). In addition, various pteridines occur in Vespa and in the honeybee (Table VI). The latter also contains xanthurenic acid (52) or kynurenic acid (53), xanthurenic acid 4,8-digiucoside (56), and a yellow pigment, xanthommatin (58), as tryptophan metabolites (Table V). 

Xanthommatin (58) is detected in blowflies of the genera Calliphora and Protophormia beside xanthurenic acid (52) and kynurenic acid (53) in the latter... 

The end products of tryptophan metabolism in the stick insect, Carausius morosus, are the ommochromes ommin and xanthommatin (58) in the epidermis, and kynurenic acid (53) in the feces. During larval development of this insect kynurenic acid (53) is the major end product of tryptophan metabolism (Table V) (109,110). Additionally, this insect contains five pteridines (Table VI), of which leucopterin (68), xanthopterin (65), and isoxanthopterin (67) are the origin of the yellow-white color of the insect (111). 

Uric acid (95) is found in various species of wood-eating termites (Isoptera, Termitidae) along with kynurenic acid (53) (Tables V and VI). Three catecholamines, adrenaline (132), noradrenaline (133), and dopamine (134), are found in the whole body of earwigs of the genus Foificula (Dermaptera, For-... 

Kynurenic acid, 6-hydroxy P1NT562 Labd-13-en-15-ol, 8-12-epoxy, 12(R)-13-trans ... 

Kynurenic acid [492-27-3] M 189.1, m 282-283°. Crystd from absolute EtOH. 

Glycines site antagonists which have been shown to be effective in analgesic models can be divided into different chemical classes although so far any high affinity effector molecule of the glycineB site bears more or less the structural motif of glycine within its molecular structure, as can be observed in the first example, kynurenic acid. 

Derivatization of kynurenic acid leads to far more potent and selective antagonists such as 7-chloro-kynurenic acid or 5,7-dichlorokynurenic acid (Kemp et al., 1988 Baron et al., 1990) which have been shown to inhibit glycine-induced tailflick facilitation (i.e attenuation of glycine-induced hyperalgesia) or the late phase of formalin-induced nociception when given intrathecally (Kolhekar et al., 1994, Chapman et al., 1995). Nevertheless kynurenic acid derivatives are still hampered by a poor blood - brain barrier penetration and hence a low CNS availability. 

Chlorokynurenic acid 5,7-Dichlorokynurenic acid Scheme 3 Structures of kynurenic acid derivatives. 

There have been further chemical attempts to improve CNS penetration such as the development of thio-kynurenic acids with improved CNS availability (Moroni et al., 1991 Chen et al., 1993). 

Other attempts make use of the better CNS penetration of kynurenine which is converted enzymatically within the brain to kynurenic acid by kynurenine aminotransferase (Hokari et al., 1996) or the design of pro-drugs which enter the CNS more easily and are hydrolyzed within the brain e g. glucosidic-linked 7-chlorokynurenic acid (Bonina et al., 2000). 

Bertolino, M., Vicini, S., Costa, E. Kynurenic acid inhibits the activation ofkainic and N-methyl-D-... 

Stone, T. W. Development and therapeutic potential of kynurenic acid and kynurenine derivatives for neuroprotection, Trends Pharmacol. Sci. 2000, 21, 149-154. 

Urenjak, J. and Obrenovitch, T. P. Kynurenine 3-hydroxylase inhibition in rats Effects on extracellular kynurenic acid concentration and N-methyl-D-aspartate-induced depolarisation in the striatum, J. Neurochem. 2000, 75, 2427-2433. 

Ultraviolet light damages proteins as well as DNA. Residues of Trp, Tyr, His, Cys, and Met are especially susceptible to photolysis, or photooxidation by 02, or by singlet oxygen. Also damaged are unsaturated lipids, porphyrins, flavins, etc. Kynurenic acid (Fig. 25-11) and urocanic acid (Eq. 14-44), an important ultraviolet filter in skin,196 are also decomposed by light. 

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