Xanthine-8-carboxylic acid

Xanthine anions structure, 5, 509 Xanthine-8-carboxylic acid synthesis, 3, 308, 322 Xanthine oxidase... 

Ring opening of 97 as indicated gives the 9-(a-amino-Q -phenylmethyl) purine 98, which by a base-catalyzed elimination of benzylideneimine is converted into 6,8-diphenyl-2-methylthiopurine 99. This pteridine-purine transformation has a close resemblance to the enzyme-catalyzed ring contraction of tetrahydropteridine into xanthine-8-carboxylic acid (64MI1), in which reaction it was proved by radioactive labeling that it is exclusively C-7 that is expelled. 

A xanthine series (I) exemplified by 33 and 34 is another important class of GPR109A agonists [83-88], It is worth noting that members of this series lack the carboxylic acid to interact with Arglll of GPR109A, unlike compounds in the aforementioned series. However, it is conceivable that the N-H present in the bicyclic core of this class of compounds is sufficiently acidic (pKa 5.6) [82] to mimic the function of a carboxylic acid present in the anthranilide class. 

This enzyme [EC 1.2.3.1] catalyzes the reaction of an aldehyde with water and dioxygen to produce a carboxylic acid and hydrogen peroxide. The enzyme uses both heme and molybdenum as cofactors. In addition, the enzyme can also catalyze the oxidation of quinoline and pyridine derivatives. In some systems this enzyme may be identical with xanthine oxidase. 

Aldehyde oxidase catalyzes the oxidation of aldehydes to carboxylic acids by dioxygen, but also catalyzes the hydroxylation of pyrimidines. Despite its rather broad specificity for substrates, it may well be that aldehyde oxidase should be regarded primarily as a pyrimidine hydroxylase. Thus, xanthine oxidase and aldehyde oxidase catalyze the hydroxylation of purines and pyrimidines respectively. The oxygen incorporated into the product comes from water, not 02. The dioxygen serves as the electron acceptor and other oxidizing agents may be used. 

Ghosh et al. [14] hypoxanthine, respectively Hypoxanthine Fish Catla- Xanthine oxidase, Conducting polypyrrole Ferrocene carboxylic acid... 

Although molybdenum and tungsten enzymes carry the name of a single substrate, they are often not as selective as this nomenclature suggests. Many of the enzymes process more than one substrate, both in vivo and in vitro. Several enzymes can function as both oxidases and reductases, for example, xanthine oxidases not only oxidize purines but can deoxygenate amine N-oxides [82]. There are also sets of enzymes that catalyze the same reaction but in opposite directions. These enzymes include aldehyde and formate oxidases/carboxylic acid reductase [31,75] and nitrate reductase/nitrite oxidase [83-87]. These complementary enzymes have considerable sequence homology, and the direction of the preferred catalytic reaction depends on the electrochemical reduction potentials of the redox partners that have evolved to couple the reactions to cellular redox systems and metabolic requirements. 

Aldehyde Oxidase. This enzyme is usually found in similar locations to xanthine oxidase or dehydrogenase and has been isolated from insects, birds, and mammals (20, 21). Aldehyde oxidase seems to be a poor choice of name for this enzyme because, while it oxidizes aldehydes to carboxylic acids, it also accepts a variety of purines and pyrimidines as oxidizable substrates. For example, aldehyde oxidase catalyzes the conversion of 2-hydroxypyrimidine to uracil and of adenine to 8-hydroxy-adenine (25). It appears that xanthine oxidase and aldehyde oxidase are... 

In addition to hydroxylating xanthine and a wide range of purines, pteridines and similar compounds, xanthine oxidase is able to oxidize aromatic and aliphatic aldehydes to the corresponding carboxylic acids. Clearly then, there is a close functional as well as structural relationship between xanthine oxidase and the eukaryotic aldehyde oxidases and prokaryotic oxidoreductases. With xanthine oxidase, the pH dependence of the kinetic parameter (obtained from the substrate concentration dependence... 

Carboxylic acids can be reacted with pentafluoro-benzyl bromide after extraction as ion-pairs with symmetrical quaternary ammonium ions at pH 7-9 [62,63]. The same process can be applied to phenols extracted at more alkaline pH values [26,27]. Xanthine derivatives... 

Xanthine oxidase is the enzyme that catalyzes the oxidation of purine, adenine, hypoxanthine, and xanthine to yield uric acid and formic acid, and the oxidation of other aldehydes to yield the corresponding carboxylic acid. 

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