Hypoxanthines

Hypoxanthine is the most versatile of the wobble bases it can base pair with adenine, cytosine, or uracil. 

This enzyme, sometimes also called the Schardinger enzyme, occurs in milk. It is capable of " oxidising" acetaldehyde to acetic acid, and also the purine bases xanthine and hypoxanthine to uric acid. The former reaction is not a simple direct oxidation and is assumed to take place as follows. The enzyme activates the hydrated form of the aldehyde so that it readily parts w ith two hydrogen atoms in the presence of a suitable hydrogen acceptor such as methylene-blue the latter being reduced to the colourless leuco-compound. The oxidation of certain substrates will not take place in the absence of such a hydrogen acceptor. 

When 6 chloropunne is heated with aqueous sodium hydroxide it is quantitatively con verted to hypoxanthine Suggest a reasonable mechanism for this reaction... 

Ibrahim and co-workers developed a new method for the quantitative analysis of hypoxanthine, a natural compound of some nucleic acids. " As part of their study they evaluated the method s selectivity for hypoxanthine in the presence of several possible interferents, including ascorbic acid. 

Xanthine oxidase, mol wt ca 275,000, present in milk, Hver, and intestinal mucosa (131), is required in the cataboHsm of nucleotides. The free bases guanine and hypoxanthine from the nucleotides are converted to uric acid and xanthine in the intermediate. Xanthine oxidase cataly2es oxidation of hypoxanthine to xanthine and xanthine to uric acid. In these processes and in the oxidations cataly2ed by aldehyde oxidase, molecular oxygen is reduced to H2O2 (133). Xanthine oxidase is also involved in iron metaboHsm. Release of iron from ferritin requires reduction of Fe " to Fe " and reduced xanthine oxidase participates in this conversion (133). 

Adenosine is formed from ATP via a phosphatase cascade that sequentially involves the diphosphate, ADP, and the monophosphate, AMP. The actions of adenosine are terminated by uptake and rephosphorylation via adenosine kinase to AMP or by cataboHsm via adenosine deaminase to inosine and hypoxanthine. 

Aristeromycin. Aristeromycin (36), the first carbocyhc analogue of adenosine, was isolated from the culture filtrates of S. citricolor as part of a search for inhibitors of bacterial leaf blight (1—4). A herbicidaHy active hypoxanthine analogue of (36), coaristeromycin, has also been isolated (108). Several chemical syntheses of (36) have appeared (1—4,109). It inhibits Aanthomonas OTjc e and Eyricularia bacterial leaf blight, blast disease of rice plants, and... 

Ara-A-5 -monophosphate [29984-33-6] (ara-AMP), C2QH24N OyP, is more water-soluble than ara-A, and therefore can be used in higher dosage during the first hours of treatment of viral infections. Ara-AMP has been shown to decrease virion-associated DNA polymerase concentrations in ground squirrels carrying ground squirrel hepatitis vims. The hypoxanthine derivative, ara-HxMP [54656-49-4] (24) is more water-soluble, appears to have a similar antiviral spectmm to ara-A, and is considerably less toxic (48). 

Guanine (Pearl Essence). Guanine (Cl Natural White 1, Cl No. 75170), is the crystalline material obtained from fish scales and consists principally of the two putines, guanine [73-40-5] (42) and hypoxanthine [68-94-0] (43). The guanine content of the colorant varies from 75% to 97%, whereas the hypoxanthine content ranges from 3% to 25%, depending on the particular fish and tissue from which the crystals ate derived. 

Hypoxanthine, 7-ethyl-synthesis, 5, 584 Hypoxanthine, 1-methyl-deuterium-hydrogen exchange, 5, 527 synthesis, 5, 594 Hypoxanthine, 2-methyl-methylation, 5, 532 synthesis, 5, 587 Hypoxanthine, 3-methyl-free radical methylation, 5, 544 irradiation, 5, 543 synthesis, 5, 584 Hypoxanthine, 8-methyl-synthesis, 5, 584 Hypoxanthine, 9-methyl-methylation, 5, 532... 

Hypoxanthine, 2-trifluoromethyl-synthesis, 5, 587 Hypoxanthine, trimethylsilyl-glycosylation, 5, 536 Hypoxanthinium nitrate, 1,3,7-trimethyl-thiation, 5, 540 Hypsochromic shift, 1, 344... 

Scott et al. [12] provided some experimental evidence supporting equation (27). The mixture contained uracil, hypoxanthine, guanine and cytosine, each present in the mobile phase at a concentration of 14 mg/1. The column employed was Im long, 1.5 mm I.D., packed with a pellicular cation exchange resin and operated at a flow rate of 0.3 ml/min. 

FIGURE 11.5 Other naturally occurring purine derivatives—hypoxanthine, xanthine, and uric acid. 

The names of 2-aza analogs are derived by formal substitution of the methine group in the 2-position of the purine skeleton by a nitrogen atom (140). Since this position is substituted in some purine bases, only the aza analogs of adenine or hypoxanthine are amenable to such formal derivation. 

---