Hypoxanthine residues

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

Carcinogenic or mutagenic metal salts have varying effects on the initiation of new RNA chains. Salts of Co (2+), Cd (2+), 

Microbial studies have demonstrated a link between carcinogenesis and mutagenesis and will be reviewed briefly with reference to the individual metals tested. 

In addition to hexavalent chromium ions, other metal ions have induced mutations in bacteria. These metals include As (3+), Cd (2+), Hg (2+), Mo (6+), Se (4+), Te (4+), Te (6+), and 

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Solid sodium nitrite (0.97 g) was added at room temperature with stirring over a period of one hour to a solution of 2-chloro-9-(2-hydroxyethoxymethyl)adenine (0.5 g) in glacial acetic acid (10 ml). The reaction mixture was stirred for an additional 41/2 hours. The white solid was removed by filtration, washed with cold acetic acid and then well triturated with cold water to remove the sodium acetate present. The solid product was retained. The combined acetic acid filtrate and wash was evaporated at reduced pressure and 40°C bath temperature and the residual oil triturated with cold water. The resulting solid material was combined with the previously isolated solid and the combined solids dried and recrystallized from ethanol to give 2-chloro-9-(2-hydroxyethoxymethyl)-hypoxanthine (0.25 g), MP>310°C. Elemental analysis and NMR spectrum were consistent with this structure. 

A mixture of 2-chloro-9-(2-hydroxyethoxymethyl)-hypoxanthine (0.375 g) and methanol (80 ml) saturated with anhydrous ammonia was heated in a bomb at 125°C for 5 hours. The bomb was cooled in an ice bath and the reaction mixture removed. Solvent and excess ammonia were removed under reduced pressure at 50°C. After the residue was triturated with cold water to remove the ammonium chloride formed, the remaining solid was dried and then recrystallized from methanol to give pure 9-(2-hydroxyethoxymethyl) guanine (0.24 g), MP 256.5-257°C. 

Hypoxanthine (2.72 g, 20 mmol) was dissolved in HMDS over 24 h under heating in the presence of TMSCI (0.5 mL). Excess solvent was removed and the residue was heated with phenethylamine (10 mL, 75 mmol) andHgCI (0.543 g, 2 mmol) for 60 h at 140 °C. Then MeOH (200 mL) was added and the solution heated for 4 h. After evaporation the residue was extracted with F.tOAc. The product crystallized from the EtOAc solution upon reduction of the volume yield 62% mp 241-244 C. 

A mixture of crude hypoxanthine (18.5 g, 0.14 mol) and PjSj (100 g, 0.45 mol) in Tetralin (500 mL) was heated at 190-200 "C with stirring for 12 h. The mixture was cooled and filtered and the solid residue washed with petroleum ether. The crude product was boiled with H O (2 L), filtered hot and the pH value of the filtrate adjusted to 4 with coned aq NH3. On standing, dark-yellow crystals of 6-sulfanylpurine hydrate precipitated yield 12 g (54%). 

Hypoxanthin-l-ol (1 g, 6.6 mmol) was suspended in a mixture of POCI, (60 mL) and Et3N (2 mL), and refluxed for 3 h. After the mixture had cooled, the excess POCI3 was distilled off under reduced pressure. The glassy residue was dissolved in H O (100 mL), and the product was continuously extracted with 130. From the EtjO extract the solvent was evaporated to yield 0.8 g of crude 2,6-dichloropurine, which was crystallized (H O) to give pure crystals yield 0.69 g (54%) mp 177"C. 

Sarkar, D., Ghosh, I., and Datta, S. (2004). Biochemical characterization of Plasmodium falciparum hypoxanthine-guanine-xanthine phosphorybosyltransferase Role of histidine residue in substrate selectivity. Mol. Biochem. Parasitol. 137,267-276. 

Karran P, Lindahl T (1980). Hypoxanthine in deoxyribonucleic acid Generation by heat-induced hydrolysis of adenine residues and release in free form by a deoxyribonucleic acid glycosylase from calf thymus. Biochem. 19 6005-6011. 

The iV- and C-atoms of the purine ring system of hypoxanthine, adenine and guanine, as well as the amino groups of these compounds carry additional substituents in several secondary products. Most frequently methyl groups, but also isoprenoid groupings, CHgS-groups and threonine residues may be present (Table 45 and Fig. 175). 

The ribose-5-phosphate residue is then removed, giving hypoxanthine, which undergoes two xanthine-oxidase-mediated oxidations to give xanthine and then uric acid (Fig. 9.14). 

Mixed leukocytes are prepared using dextran sedimentation of erythrocytes, centrifugation of leukocytes from the plasma, and lysis of residual erythrocytes with ammonium chloride. Granulocytes and mononuclear leukocytes are separated from each other and from erythrocytes by density gradient centrifugation using a mixture of Ficoll, Hypaque and dextran. Thirty ml of blood provides sufficient leukocytes for study of adenine, guanine and hypoxanthine metabolism in duplicate. Suspension cultures of human lymphoblasts and leukemic cells, and monolayer cultures of skin fibroblasts and amnionic cells were studied under normal culture conditions approximately 10 cells are required for each incubation. 

In order to determine whether the released adenosine could serve as a precursor of human erythrocyte adenine nucleotides, a rabbit liver was labeled by perfusion with Hj -hypoxanthine as described. Washout perfusion with an isotonic balanced salt solution removed residual extracellular label. The labeled liver was then perfused by recirculating a 400ml washed human erythrocyte suspension for one hour. Erythrocytes were then collected and washed, and the liver was excised. Extracts were prepared and the purine nucleotides were assayed for distribution of radioactivity (Table II). Within the liver, the radioactivity was approximately evenly distributed between the adenine nucleotides and the hypoxanthine plus xanthine nucleotides, indicating again that extensive conversion of hypoxanthine to IMP to AMP can occur in the liver cell. Within the human erythrocyte, over 80 percent of the label appeared in the adenine nucleotides. Since IMP is not converted to AMP in that cell, the labeled adenosine formed in the liver from the perfused hypoxanthine must have been taken up by the human erythrocyte and converted to AMP by the adenosine kinase. Since free adenine, the only other possible precursor of human erythrocyte adenine nucleotides, was not detected in hypoxanthine perfused liver or in hepatic venous effluent from hypoxanthine perfused liver, a possible role is unlikely. 

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