Xanthine 2,6-Dihydroxypurine

The anaerobe Peptococcus (Micrococcus) aerogenes had a dehydrogenase that carried out specific hydroxylation at the 6-positions of 2- and 8-hydroxypurine, and was therefore distinct from xanthine dehydrogenase from which it could be separated (Woolfolk et al. 1970). It was also able to carry out dismutation of 2-hydroxypurine to xanthine (2,6-dihydroxypurine) and hypoxanthine (6-hydroxypurine). 

Gout is caused by the deposition of crystals of monosodium urate hydrate which are ingested by leucocyctes and trigger the inflammatory response. The biosynthesis of uric acid involves the oxidation of the more soluble compound xanthine (2,6-dihydroxypurine) by xanthine oxidase, and this enzyme is inhibited by allopurinol (187). The treatment of gout also relies on uricosuric drugs to accelerate urinary excretion of uric acid and antiinflammatory drugs to ease the pain and inflammation. 

Cytosine (2-hydroxy-6-amino-pyrimidine), uracil (2,6-dihydroxypyrimidine), and thymine (5-methyluracil) are pyrimidine derivatives adenine (6-aminopurine), guanine (2-amino-6-hy-droxypurine), and xanthine (2,6-dihydroxypurine) are purine derivatives (Fig. 5). 

Other key derivatives, xanthine (2,6-dihydroxypurine, 4) and hypoxanthine (6-hydroxypurine, 5), are formed by the hydrolytic decomposition of nucleic acids. As their systematic names indicate, the well-known CNS stimulants caffeine (1,3,7-trimethylxanthine, 6), theophylline (1,3-dimethylxanthine), and theobromine (3,7-dimethyl-xanthine), found in coffee, tea, and cocoa beans, respectively, are all derived from xanthine. 

Xanthine 32 (2,6-dihydroxypurine), mp 262°C, is chemically similar to uric acid (see below). It is soluble in bases and acids and forms a sparingly soluble perchlorate. Xanthine is prepared from cyanoacetic ester and urea by way of 4-aminouracil 31 (according to the Traube principle), or from uric acid 33 by heating with formamide (Bredereck 1950) ... 

Dihydroxypurine, see under Xanthine 2,8-Dihydroxypurine, IX, 138 2,4 Dihydroxypyrimidine, see under Uracil... 

Xanthine, Xan 2,6-dihydroxypurine, a purine and the starting point for Purine degradation (see). 152.1, m.p. >400°C (d.). Xan was discovered in 1817 in renal stones. It occiu in the free form, accompanied by other purines. Some derivatives are physiologically important, in particular xanthosine phosphates and Methylated xanthines (see). 

Xanthine, or 2,6-dihydroxypurine, was first associated with caffeine in certain plants. It was later found in urine, blood, and liver. In 1817, Marcet detected xanthine in renal calculi. Xanthine was synthesized from chloropurine or from 4-aminouracil. An addition to its biological significance as the product of nucleic acid degradation (deamination of guanine or oxidation of hypoxanthine), xanthine is also important as an... 

Xanthine (30, 2,6-dihydroxypurine), mp 262 °C, is chemically similar to uric acid (see below). It is soluble in bases and acids and forms a sparingly soluble perchlorate. 

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