3-Methyl-2 -deoxyuridine

Methyl-2 -deoxycytidine (437) and 3-methyl-2 -deoxyuridine (438) were isolated from the Swedish sponge Geodia baretti. Compound 437 exhibits strong contractile activity in the isolated guinea pig ileum assay, whereas 438 had no effect on contractions (356). Thymidine-5 -carboxylic acid (439) and 2 -deoxyuridine-5 -carboxylic acid (440), which were previously known only as synthetic products, were found in extracts of the ascidian Aplidium fuscum of the East Pyrenean coast (357). 

The best-known example of this type of inhibition is 5 -fluorouracil, a rather old cytostatic agent. Fluorouracil is first converted metabolically into the corresponding phosphodeoxyriboside. This, in turn, blocks DNA biosynthesis by inhibiting thy-midylate synthase, an enzyme which methylates deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP), one of the four building blocks of DNA [77]. 

Methyl deoxyuridine (base) ti/2 24hwithPO Intermolecular affinity — f [64]... 

The methylation of deoxyuridine monophosphate (dUMP) to thymidine monophosphate (TMP), catalyzed by thymidylate synthase, is essential for the synthesis of DNA. The one-carbon fragment of methy-lene-tetrahydrofolate is reduced to a methyl group with release of dihydrofolate, which is then reduced back to tetrahydrofolate by dihydrofolate reductase. Thymidylate synthase and dihydrofolate reductase are especially active in tissues with a high rate of cell division. Methotrexate, an analog of 10-methyl-tetrahydrofolate, inhibits dihydrofolate reductase and has been exploited as an anticancer drug. The dihydrofolate reductases of some bacteria and parasites differ from the human enzyme inhibitors of these enzymes can be used as antibacterial drugs, eg, trimethoprim, and anti-malarial drugs, eg, pyrimethamine. 

In 1995, Horie et al. described a polymorphic tandem repeat found in the 5 -un-translated region of the thymidylate synthase gene [70]. Thymidylate synthase (TS TYMS) catalyzes the intracellular transfer of a methyl group to deoxyuridine-5-monophosphate (dUMP) to form deoxythymidine-5-monophosphate (dTMP), which is anabolized in cells to the triphosphate (dTTP). This pathway is the only de- novo source of thymidine, an essential precursor for DNA synthesis and repair. The methyl donor for this reaction is the folate cofactor 5,10-methylenetetrahydro-folate (CH2-THF) (Figure 24.4). 

Using phosphotriester methods, dinucleoside (3 - 50-monophosphates containing 6-methyl-2,-deoxyuridine at the 3 - or 5 -end have been prepared.44 N.m.r. spectroscopy indicates that this nucleoside possesses the syn conformation in these compounds, and, on treatment with snake venom phosphodiesterase, d(m6UpT) is degraded, while d(Apm6U) is not, indicating that this enzyme, a 3 -exonuclease, requires the anti conformation to be present in the substrate. Two modified nucleo-side-5 -monophosphates, (20) and (21), which are resistant to 5 -nucleotidase, have been isolated from tRNA snake venom hydrolysates.45 A synthesis of (20) has been reported.46... 

Dideoxyuridine (ddU) is an antiviral agent that proved ineffective at controlling human immunodeficiency virus type 1 (HIV-1) infection in human T-cells. This ineffectiveness was ascribed to a lack of substrate affinity of ddU for cellular nucleoside kinases, which prevent it from being metabolized to the active 5 -triphosphate. To overcome this problem, bis[(pivaloyloxy)methyl] 2, 3 -dideoxyuridine 5 -monophosphate (9.41) was prepared and shown to be a membrane-permeable prodrug of 2, 3 -di-deoxyuridine 5 -monophosphate (ddUMP, 9.42) [93]. Indeed, human T-cell lines exposed to 9.41 rapidly formed the mono-, di-, and triphosphate of ddU, and antiviral activity was observed. This example again documents... 

Thymidylate synthase [EC 2.1.1.45] reductively methylates 2 -deoxyuridine-5 -monophosphate to form 2 -deoxythymidine-5 -monophosphate in the following folate-dependent reaction dUMP + A, A -methylene-tetrahydrofolate dTMP + dihydrofolate. 

The HPLC-MS/MS method has been recently applied for the measurement of the cis and trans diastereomers of 5,6-dihydroxy-5,6-dihydrothymidine (8), 5-formyl-2 -deoxyuridine (11) and 5-(hydroxymethyl)-2 -deoxyuridine (10) within cellular DNA exposed to ionizing radiation and heavy particles. The two methyl oxidation products 10 and 11 and thymidine glycols 8 (Chart 3) that are produced within the range of 20 to 100 lesions per 10 normal bases and per Gy (Table 3) are likely to be derived from the decomposition of 5-(hydroperoxymethyl)-2 -deoxyuridine (7) and 5-(6)-hydroperoxy-6-(5)-hydroxy-5,6-dihydrothymidine 5 and 6, respectively. 

The TS mediates the conversion of 2-deoxyuridine monophosphate (dUMP) into deoxythymidine monophosphate (dTMP). This enzymatic methylation reaction is a key step in the synthesis of DNA and involves a ternary complex between the substrate, the enzyme and the co-factor [methylene tetrahydrofolic acid (CH2FAH4)] (Fig. 24) [8,80,81], This transformation represents the sole de novo source of dTMP, a building block for DNA synthesis and repair [82]. 

Thymidylate synthase (TS) is the enzyme that converts 2-deoxyuridine monophosphate into thymidine monophosphate. This is a key step in the biosynthesis of DNA. This enzymatic reaction of methylation involves the formation of a ternary complex between the substrate, the enzyme, and tetrahydrofolic acid (CH2FAH4). The catalytic cycle involves the dissociation of this complex and the elimination of FAH4. It is initiated by pulling out the proton H-5, thus generating an exocyclic methylene compound. As the release of a F" " ion is energetically forbidden, the fluorine atom that replaces the proton H-5 cannot be pulled out by the base. This leads to inhibition of the enzyme (Figure 7.2). 

The other major class of antimalarials are the folate synthesis antagonists. There is a considerable difference in the drug sensitivity and affinity of dihydrofolate reductase enzyme (DHFR) between humans and the Plasmodium parasite. The parasite can therefore be eliminated successfully without excessive toxic effects to the human host. DHFR inhibitors block the reaction that transforms deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) at the end of the pyrimidine-synthetic pathway. This reaction, a methylation, requires N °-methylene-tetrahydrofolate as a carbon carrier, which is oxidized to dihydrofolate. If the dihydrofolate cannot then be reduced back to tetrahydrofolate (THF), this essential step in DNA synthesis will come to a standstill. 

Chatgilialoglu C, Ferreri C, Bazzanini R, Guerra M, Choi S-Y, Emanuel CJ, Horner JH, Newcomb M (2000) Model of DNA Cl radical. Structural, spectral and chemical properties of the thyminyl-methyl radical and the2 -deoxyuridin-1 -yl radical. J Am Chem Soc 122 9525-9533... 

A metabolic pathway that has received considerable attention is the conversion of 2 -deoxyuridine 5 -monophosphate (dUMP, 6.60) to thymidine 5 -monophosphate (TMP, 6.61) (Scheme 6.13). Without an adequate supply of TMP, a cell or bacterium cannot create DNA for cell division. Therefore, blocking TMP synthesis is an attractive method for slowing the advancement of certain cancers and bacterial infections. Important molecules in the methylation of dUMP are the various folic acid derivatives folic acid (FA, 6.62), dihydrofolic acid (DHF, 6.63), tetrahydrofolic acid (THF, 6.64), and N5, A1 "-methylene tetrahydrofolic acid (MTHF, 6.65) (Figure 6.23). These structures... 

The thymidylate synthase reaction involves the methylation of deoxy-UMP to deoxy-TMP (thymidylate). Deoxy-UMP is the result of dephosphorylation of the product of the ribonucleotide reductase reaction, dUDP. The conversion of the diphosphate nucleotide to the monophosphate nucleotides helps channel deoxyuridine to thymidylate synthase rather than directly to DNA. N5,N10-methylene tetrahy-drofolate donates the methyl. 

A remote-controlled system has been developed269 for the production of 214, presented in equation 132. The system is also useful for production of 5-ethyl-[nC]-2 -deoxyuridine, 6-methyl-[nC]-2 -deoxyuridine and other nucleosides269. 214 is a tracer for measuring cell proliferation in fast dividing tissue and tumor visualization by PET270-272. 

Photochemical reaction in acetonitrile of 2 -deoxyuridine 5 -phosphate with the halo-heteroarenes 2-iodothiophene, 2-iodofuran, l-methyl-2-iodopyrrole and 3-iodothiophene affords the C-5 heteroaryl substituted nucleotides518.6-Aryluridines have been prepared by irradiation of 6-iodouridines in benzene, anisole, thiophene, Af-methylpyrrole or 2-methyl-furan in the presence of triethylamine519. 

A. S. Jones and coworkers72 attempted a synthesis of 5 -(carboxy-methyl)-5 -deoxyuridine (111) as a nucleotide analog, starting from 2, 3 -0-isopropylideneuridine-5 -aldehyde (112) and ethoxycarbonyl-methylenetriphenylphosphorane. Surprisingly, no reaction occurred. When the phosphorane was generated in situ by means of sodium eth-oxide, a mixture of five products was obtained. Four of them were... 

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