Purine water elimination

In the purine series, water eliminations such as reactions (32) and... 

With [ N2]hydrazinium hydrogen sulfate and potassium hydroxide, the 2, 3, 5 -tri-0-acetyl-l-( N-amino) (3- N) inosine 54 is obtained (Scheme III.29). The reaction follows the same reaction pathway as described in Scheme III.28 addition of the nucleophile at C-6, ring opening between C(6) and N(l), and ring closure with elimination of nitrous oxide and water. This Sn(ANRORC) reaction provides us with an good entry to N-ring-labeled purines. 

Of these radicals, 60-70% have oxidizing properties (for the reactions of purine- OH-adducts with a number of reductants see, e.g., O Neill 1983, 1984 O Neill et al. 1985 Shi et al. 1999a Candeias and Steenken 2000). This includes the -OH-adducts that eliminate rapidly water yielding G (Steenken 1989). Its main precursor has been has been suggested to be the C(4)- OH-adduct (-60-70% Vieira et al. 1993 Candeias and Steenken 2000). This radical eliminates water leading to the even more strongly oxidizing G- [cf. reaction (77)]. 

Moorthy PN, Hayon E (1975) Free-radical intermediates produced from the one-electron reduction of purine, adenine and guanine derivatives in water. J Am Chem Soc 97 3345-3350 Mori M, Teshima S-l, Yoshimoto H, Fujita S-l, Taniguchi R, Hatta H, Nishimoto S-l (2001) OH Radical reaction of 5-substituted uracils pulse radiolysis and product studies of a common redox-ambivalent radical produced by elimination of the 5-substituents. J Phys Chem B 105 2070-2078 Morin B, Cadet J (1995) Chemical aspects of the benzophenone-photosensitized formation of two lysine - 2 -deoxyguanosine cross-links. J Am Chem Soc 117 12408-12415 Morita H, Kwiatkowski JS,TempczykA(1981) Electronic structures of uracil and its anions. Bull Chem Soc Jpn 54 1797-1801... 

Each base has a nitrogen atom capable of forming an acetal-like bond to the anomeric (or hemiacetal) carbon of deoxyribose. Recall that formation of an acetal from an alcohol and a hemiacetal involves elimination of water. We can envision that the water molecule is formed from the hydroxyl group of the hemiacetal and a hydrogen atom from the alcohol (or, in this case, the amine). Figure 12.57 illustrates this reaction for a purine base and for a pyrimidine base. 

Allopurinol reduces the amount of uric acid in blood and urine by slowing the rate at which the liver produces uric acid. It does this by inhibiting an enzyme, xanthine oxidase. This enzyme normally catalyses the later stages of metabolism of purines to uric acid. As a result of xanthine oxidase inhibition less uric acid is produced. Intermediate metabolites xanthine and hypoxanthine are produced in larger amounts, but these are freely water soluble and eliminated by the kidneys. 

We must now consider which functional groups are involved in the assembly of these compounds. In the case of the formation of a nucleoside, the nitrogen atom number 3 of a pyrimidine base or the nitrogen atom number 9 of a purine base becomes linked to the carbon atom number 1 of the pentose sugar, with the elimination of water. According to the conventions of sugar chemistry the carbon atom number 1... 

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