Deoxyuridine from deoxycytidine

Dihydro-5-aZathymidine. 5,6-Dihydro-5-azathymidine [57350-36-4] (177), C9H15N305, contains the x-triazine ring and is isolated from the culture filtrates of S. platensis var. clarensis (4). The inhibition of vital replication by (177) can be reversed by either thymidine, deoxyuridine, or deoxycytidine. Compound (177) protects mice following intracerebral inoculation with HSV-1 and appears to inhibit the phosphorylation of thymidine rather than its incorporation into DNA. Resistance to (177) by E. coli appears to result from a change in thymidine phosphorylase. 

The synthesis of deoxyuridine, cytidine, deoxycytidine and thymidine nucleotides from UMP (Fig. 6.13) involves three reactions CTP synthetase, ribonucleotide reductase, and thymidylate synthase (80). The first enzyme converts UTP into CTP and the second catalyzes the conversion of CDP, UDP, ADP and GDP into their respective deoxyribonucleotides. The last enzyme, thymidylate synthase, catalyzes the reductive methylation of deoxyUMP at the C-5 position giving deoxyTMP. The human enzyme has been extensively studied as it is a target enzyme in cancer chemotherapy. Besides these three enzymes, two other enzymes are involved in pyrimidine nucleotide synthesis and interconversion. DeoxyCMP deaminase converts deoxyCMP into deoxyUMP and deoxyUTP triphosphatase converts deoxyUTP into deoxyUMP. Giardia lamblia, and Trichomonas vaginalis lack both ribonucleotide reductase and thymidylate synthase and... 

There have been many reports of syntheses of deoxy nucleosides by standard sugar-base condensation reactions. These include 5 -deoxy-ribo nucleosides and 5 -mono- or 5",5-di-deuterated analogues, as well as derivatives of 5-deoxy-D-xylose and 5-deoxy-D-glucose, 5-alkylated thymidine derivatives, 2 -deoxy-6-methyl-5-azacytidine and its a-anomer, the thymidine analogue 4-(2-deoxy-B-D-erythro-pento-furanosyl)-6-methyl-l,2,4-triazine 3(HH)-one-1-oxide, 6-aza-3-deaza analogues of 2 -deoxy-cytidine and 2 -deoxyuridine,3 -deoxycytidine from a 3-deoxy-ribofuranose obtained from a fermentation broth producing the 3 -deoxy nucleoside antibiotic, cordycepin, 4-deoxy-DL-threo-pentopyranosyl pyrimidine nucleosides, and 5 -C-methyluridines derived from 6-deoxy-D-allose and 6-deoxy-D-talose. A range... 

Other degradation products of the cytosine moiety were isolated and characterized. These include 5-hydroxy-2 -deoxycytidine (5-OHdCyd) (22) and 5-hydroxy-2 -deoxyuridine (5-OHdUrd) (23) that are produced from dehydration reactions of 5,6-dihydroxy-5,6-dihydro-2 -deoxycytidine (20) and 5,6-dihydroxy-5,6-dihydro-2 -deoxyuridine (21), respectively. MQ-photosen-sitized oxidation of dCyd also results in the formation of six minor nucleoside photoproducts, which include the two trans diastereomers of AT-(2-de-oxy-/j-D-eryf/iro-pentofuranosyl)-l-carbamoyl-4 5-dihydroxy-imidazolidin-2-one, h/1-(2-deoxy-J8-D-crythro-pentofuranosyl)-N4-ureidocarboxylic acid and the a and [5 anomers of N-(2-deoxy-D-eryfhro-pentosyl)-biuret [32, 53]. In contrast, formation of the latter compounds predominates in OH radical-mediated oxidation of the pyrimidine ring of dCyd, which involves preferential addition of OH radicals at C-5 followed by intramolecular cyclization of 6-hydroperoxy-5-hydroxy-5,6-dihydro-2 -deoxycytidine and subsequent generation of the 4,6-endoperoxides [53]. 

The most important pyrimidine derivatives are those upon which biological organisms depend. Cytosine 1018 and uracil 1019 are found in ribonucleic acid (RNA) in the form of their ribonucleotides, cytidine 1020 and uridine 1021, while in deoxyribonucleic acid (DNA), cytosine and thymine 1022 are found in the form of their 2 -deoxyribonucleotides, 2 -deoxycytidine 1023 and thymidine 1024. 5-Methylcytosine 1025 is also found to a small extent (c. 5%) in human DNA in the form of its 2 -deoxyriboside 1026, and 5-(hydroxymethyl)cytosine-2 -deoxyriboside 1027 has also been detected in smaller amounts <2005CBI1>. Many variants of cytosine and uracil can be found in RNA including orotic acid 1028 in the form of its ribonucleotide orotidine 1029. Other pyrimidine derivatives to have been isolated from various biological sources include 2 -deoxyuridine 1030, alloxan 1031, and toxopyrimidine (pyramine) 1032 (Figure 2). 

The synthesis of a 2 -amino-2 -deoxyuridine 168 and a 2 amino-2 deoxycytidine 169 from inexpensive uridine has been described. A key transformation in the synthesis is the introduction of an amino functionality via a trichloroacetimidate. This approach also avoids the use of azide that is not desirable for large-scale use (Scheme 8.48). 

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). 

Sources of deoxyuridine in DNA include the presence of dUTP because dUMP (the substrate for thymidylate synthase) or dUDP (from ribonucleotide reductase action on UDP) are phosphorylated to the triphosphate. DNA polymerase recognizes these compounds as substrates. Another source is the deamination of deoxycytidine in DNA, promoted by a variety of compounds. If deoxyuridine is on a template strand of the DNA, it will direct the incorporation of an A in the newly made strand of DNA. This will convert a G-C pair to an A-T pair. 

The H-phosphonate derivative of a tricyclic carbazole-like 2 -deoxycytidine (183) analogue has been synthesised via a Stille biaryl coupling on 5-iodo-2 -deoxyuridine followed by cyclisation. The carbazole nucleoside was incorporated in oligonucleotides and shown to pair specifically with guanine. Duplexes resulting from the carbazole analogue and complementary RNA have elevated... 

E. coli cytidine deaminase (CDA) is an enzyme that catalyzes hydrolytic deamination of cytidine to uridine (or from 2 -deoxycytidine to 2 -deoxyuridine) (Scheme 8). This enzyme is considered to be a member of the MMP family, although the Zn -binding site contains two Cys and one His residues. On the basis of the X-ray crystal structure of a transition-state analogue complex,a mechanism was proposed as shown in Scheme 8, in which Glul04 serves multiple roles the deprotonation of the Zn " -bound water and simultaneous protonation to N3 of the substrate (Scheme 8a), stabilization of the first tetrahedral transition state (Scheme 8b), and protonation of the leaving amino group at the 4-position of the substrate in the second tetrahedral intermediate (Scheme 8c).Upon elimination of NH3, an E-P complex is formed (Scheme 8d) and the enzyme goes into the next turnover. The deamination mechanism of E. coli... 

Metabolism of the pyrimidine deoxyribonucleotides is more complex because, in addition to transfer of phosphoryl groups, deamination and methylation reactions occur at this level. Specifically, the thymidine phosphates are derived by methylation of deoxyuridylate, and the latter may be derived from the deoxycytidine phosphates by way of deoxycytidylate deaminase. The deoxycytidine phosphates are not formed by amination of deoxyuridine phosphates, but are derived entirely from the cytidine phosphates by enzymatic reduction (Chapter 16). 

Deoxyuridine and thymidine are substrates for pyrimidine nucleoside phosphorylases, but deoxycytidine (and cytidine) is generally regarded as being inert to phosphorolysis (7) Tarris demonstration of deoxycytidine formation from cytosine in extracts of fish milt is an exception to this generalization (8). Catabolism of C3rtosine nucleosides is initiated by deamination to form uracil nucleosides which can be phosphorolyzed. 

The methylation of the pyrimidine nucleus by one-carbon compounds was in accord with the earlier suggestion that thymine formation in the rat proceeded by direct conversion of C3rtidine or a closely related structure to thymidine (317). Further agreement came from studies in rabbit bone marrow and in Ehrlich ascites tumor cells in vitro, where it was demonstrated that both c rtidine and deoxycytidine (and to a lesser extent uridine and deoxyuridine) stimulated the incorporation of formate-C into DNA thymine (338). 

The cytidine and inosine analogues in the 4 -azido-2 -deoxy series were made by well known procedures from the uridine and adenosine analogues, respectively (Scheme II). Thus, following the method of Reese, 4 -azido-2 -deoxyuridine was acetylated and then converted to the 4-triazolide, which on treatment with ammonium hydroxide furnished 4 -azido-2 -deoxycytidine. Using a procedure of Herdewijn, 4 -azido-2 -deoxyadenosine was enzymatically deaminated to the inosine analogue. 

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