Uracil oxidation

Because the incorporation of the methyl group into uracil oxidizes tetrahydrofolate to dihydrofolate, dihydrofolate must be reduced back to tetrahydrofolate to prepare the coenzyme for another catalytic reaction. The reducing agent is NADPH. 

The problem of pyrimidine degradation by microorganisms has been studied primarily by enrichment culture techniques. By this method, bacterial strains were grown that utilized pyrimidines as their source of nitrogen and carbon intact cells, as well as purified enzymes obtmned from such bacteria, were investigated (296, 390-392). Pyrimidines were converted to barbituric acid by cell-free extracts of the soil bacterium, strain U-1, which indicated that the initial oxidation of the pyrimidine ring occurred at carbon 6 (392) (Kg. 23). There was no converaon of uracil to isobarbituric acid (391). Barbituric acid was also obtained as a product of uracil oxidation by strains of Corynehacterium and Mycobacterium... 

Later, a completely different and more convenient synthesis of riboflavin and analogues was developed (34). It consists of the nitrosative cyclization of 6-(A/-D-ribityl-3,4-xyhdino)uracil (18), obtained from the condensation of A/-D-ribityl-3,4-xyhdine (11) and 6-chlorouracil (19), with excess sodium nitrite in acetic acid, or the cyclization of (18) with potassium nitrate in acetic in the presence of sulfuric acid, to give riboflavin-5-oxide (20) in high yield. Reduction with sodium dithionite gives (1). In another synthesis, 5-nitro-6-(A/-D-ribityl-3,4-xyhdino) uracil (21), prepared in situ from the condensation of 6-chloro-5-nitrouracil (22) with A/-D-ribityl-3,4-xyhdine (11), was hydrogenated over palladium on charcoal in acetic acid. The filtrate included 5-amino-6-(A/-D-ribityl-3,4-xyhdino)uracil (23) and was maintained at room temperature to precipitate (1) by autoxidation (35). These two pathways are suitable for the preparation of riboflavin analogues possessing several substituents (Fig. 4). 

In contrast, the photochemistry of uracil, thymine and related bases has a large and detailed literature because most of the adverse effects produced by UV irradiation of tissues seem to result from dimer formation involving adjacent thymine residues in DNA. Three types of reaction are recognizable (i) photohydration of uracil but not thymine (see Section 2.13.2.1.2), (ii) the oxidation of both bases during irradiation and (iii) photodimer formation. 

The best direct synthetic route to uracil is probably the classical procedure from malic acid and urea in concentrated sulfuric acid (26JA2379), despite efforts to use maleic acid, urea and polyphosphoric acid (71S154) or propiolic acid, urea and a little concentrated sulfuric acid (77JOC2185) to achieve the same result. However, the most convenient source (apart from purchase) is to convert 2-thiouracil (937 X = S) into uracil by boiling with aqueous chloroacetic acid (52MI21300) or perhaps by oxidation with DMSO in strong sulfuric acid (74S491). 

There are many synthetic routes to alloxan. Probably the best is direct oxidation of barbituric acid (1004 R = H) with chromium trioxide (5208(32)6) but it may be made from barbituric acid via its benzylidene derivative by direct or indirect oxidation of uric acid from 5-chlorobarbituric acid (1004 R = C1) by nitration or from 5-nitrobarbituric acid (1004 R = N02) by chlorination, both via the intermediate (1005) (64M1057) or by permanganate oxidation of uracil (1006) under carefully controlled conditions (73BSF1167). 

Oxidative cyclization of the fully methylated 6-(benzylidenehydrazino)uracils (536) provides a 90% yield of the pyrazolo[3,4-J]pyrimidines (537) (75BCJ1484). 

Uracil, 5-methoxy-6-methoxymethyl-2-thio-synthesis, 3, 134 Uracil, 1-methyl-aminolysis, 3, 91 synthesis, 3, 110 Uracil, l-methyl-5,6-dihydro-synthesis, 3, 110 Uracil, 6-methyl-3-phenyl-synthesis, 3, 110 Uracil, 3-methyi-2-thio-synthesis, 3, 112 Uracil, 6-methyl-2-thio-oxidation, 3, 94 Uracil, 5-nitro-... 

Eosin Flavonoids Morin Flavonol, fisetin, robinetin Quercetin Rutin condensation products of urea, formaldehyde and methanol [126], pesticide derivatives [127] sweetening agents [128, 129] anion-active and nonionogenic surface-active agents [130] steroids, pesticides [29,132, 133] pesticides [134—137] vanadium in various oxidation states [138] uracil derivatives [139]... 

The 1,3-dimethyluracil derivative 109 with two reactive centers reacts with 1,2,4-tiiazine 4-oxide 58 only at the uracil fragment to afford compound 110 (96MC116). 

Preparation of 5-[bis/2-Hydroxyethyl)Amino] Uraci/ 20 grams (0.157 mol) of 5-amlno-uracil was mixed with 350 ml of water, 23 ml of glacial acetic acid, and 160 ml of ethylene oxide in a one-liter flask immersed in an ice bath. The reaction mixture was stirred and allowed to come to room temperature slowly (as the ice melted), and stirring was continued for two days. A clear solution resulted to which was added 250 ml of water and 60 grams of Dowex-50 in the acid form. The mixture was stirred for 15 minutes, and the resin was collected on a filter. It was washed with water and the crude 5-[bis(2.hydroxy-ethyl)amino] uracil was eluted with a 10% aqueous solution of ammonium hydroxide. 

Triethylenemelamine Ethylene oxide Chlorambucil Choline dihydrogen citrate Etofibrate Melphalan Nimorazole Nonoxynol Tyloxapol Uracil mustard... 

The final step in the metabolic degradation of uracil is the oxidation of malonic semialdehyde to give malonvl CoA. Propose a mechanism. 

The one-pot MCR of methylene active nitriles 47 has been used in the synthesis of both pyrano- and pyrido[2,3-d]pyrimidine-2,4-diones in a single-mode microwave reactor [90]. Microwave irradiation of either barbituric acids 61 or 6-amino- or 6-(hydroxyamino)uracils 62 with triethyl-orthoformate and nitriles 47 (Z = CN, C02Et) with acetic anhydride at 75 °C for 2-8 min gave pyrano- and pyrido[2,3-d]pyrimidines in excellent yield and also provided a direct route to pyrido[2,3-d]pyrimidine N-oxides (Scheme 27). 

The key metabolites of caffeine (a trimethylxanthine) found in plasma, are the dimethylxanthines paraxanthine, theophylline, and theobromine the monomethylxanthine 1-methylxanthine the C-8 oxidized monomethylxanthine 1-methyluric acid and the ring oxidized uracil 5-acetyl-amino-6-amino-3-methyluracil. 

Electron-rich 6-[(dimethyl(amino)methylene)amino uracil 82 underwent [4+2] cycloaddition reactions with various in situ generated glyoxylate imine and imine oxides to afford novel pyrinhdo[4,5-J]pyrimicline derivatives 83-84 after elimination of dimethylamine from the (1 1) cycloadducts and oxidative aromatization. This one-pot procedure yielded excellent yields when carried out in the solid state and under microwave irradiation <06BMCL3537>. 

Treating glycosyl isothiocyanates 415 with 5,6-diamino-1,3-dimethyl-uracil (416) gave thioureas 417, which on oxidative cyclization with N-bromosuccinimide afforded 5,7-dioxopyrimido[5,4- ][1,2,4]triazine nucleosides 418 (80MI1 82MI2). 

Phenylglyoxal and alkoxyphenylglyoxals react selectively with the guanine moiety of nucleosides and nucleotides in phosphate buffer (pH 7.0) at 37°C for 5-7 min to give the corresponding fluorescent derivatives [12-15], as shown in Figure 6. Other nucleic acid bases and nucleotides (e.g., adenine, cytosine, uracil, thymine, AMP, CMP) do not produce derivatives under such mild reaction conditions. The fluorescent derivative emits chemiluminescence on oxidation with di-methylformamide (DMF) and H202 at pH 8.0-12 [14, 15],... 

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