Deoxyuridine monophosphate conversion

Fluorouracil (5-fluorouracil, 5-FU, Fig. 5) represents an early example of rational drag design in that it originated from the observation that tumor cells, especially from gut, incorporate radiolabeled uracil more efficiently into DNA than normal cells. 5-FU is a fluorinated pyrimidine analog that must be activated metabolically. In the cells 5-FU is converted to 5-fluoro-2>deoxyuridine-monophosphate (FdUMP). This metabolite inhibits thymidilate synthase which catalyses the conversion of uridylate (dUMP) to thymidilate (dTMP) whereby methylenetetrahydrofo-late plays the role of the carbon-donating cofactor. The reduced folate cofactor occupies an allosteric site of... 

Trifluridine (Viroptic) is a fluorinated pyrimidine nucleoside that has in vitro activity against HSV-1 and HSV-2, vaccinia, and to a lesser extent, some adenoviruses. Activation of trifluridine requires its conversion to the 5 monophosphate form by cellular enzymes. Trifluridine monophosphate inhibits the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) by thymidylate synthetase. In addition, it competes with deoxythymidine triphosphate (dTTP) for incorporation by both viral and cellular DNA polymerases. Trifluridine-resistant mutants have been found to have alterations in thymidylate synthetase specificity. 

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]. 

The folic acid-dependent conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) carried out by thymidylate synthase is an absolute requirement for DNA synthesis. An unusually high demand for uracil (ura) by certain tumor cells suggested that such an inhibitor of this process could have tumor cell selectivity. 5-Fluorouracil (fl5ura) (80), along with 5-fluorocytosine (fl5cyt) (81) and 5-fluoroorotic acid (fl5oro) (82), were synthesized by Heidelberger in 1957 as part of a... 

Several analytes are known to be indicative of folate metabolism. Plasma total homocysteine increases when there is a deficiency of 5-MTHF, such that the methylation of homocysteine to methionine is compromised. However, though plasma homocysteine is considered to be a sensitive functional indicator, it is not specific because its concentration can be influenced by deficiency of other vitamins (Bg and B12) involved in the metabolism of homocysteine. Similarly the methylation of DNA is dependent upon adequate 5-MTHF. A sensitive new method for the rapid detection of abnormal methylation patterns in global DNA patterns has been reported and may have promise as a functional marker, as may the measurement of the degree of uracil incorporation into DNA, 5,10-metliylene THF being required for die conversion of deoxyuridine monophosphate (dUMP) to dTMP by thymidylate synthetase. ... 

Of the two objectives (Section I) of investigations on the models of this cofactor, the one translating its functional capability of carbon transfers in the evolution of chemical synthesis has been amply illustrated. With respect to the second objective of providing support to the molecular mechanism of the enzymatic process in which this cofactor plays an essential role, Pandit chose to mimic in totality the thymidylate synthase (TS) catalyzed conversion of deoxyuridine monophosphate (dUMP, 129) to deoxythymine monophosphate (dTMP, 131) that is reported to proceed by transfer of a methylene group of an imidazolidine component of 1 to C-5 of dUMP 129, the nucleophilicity of which is enhanced by the addition of a thiol of apoenzyme at C-6, generating the methylene intermediate 130. The subsequent delivery of the C-6H of 1 as an hydride equivalent to the methylene carbon is followed by elimination of a thiol and formation of dTMP 131 along with 7,8-dihydrofolate 132. 

Scheme 14.12. A representation of a potential pathway for the conversion of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) while tetrahydrofolate is oxidized to dihydrofolate using nicotinamide adenine dinucleotide (NAD /NADH). EC numbers and some graphic materials in this scheme have been taken from appropriate links in a URL starting with http //www.chem.qmul.ac.uk/iubmb/enzyme.

Thymidylate Synthase (TS) is a 70 kDa dimeric protein that catalyzes the conversion of 2 -deoxyuridine 5 -monophosphate (dUMP) into 2 -deoxythymidine 5 -monophosphate (dTMP) using 5,10-methylene-5,6,7,8-tetrahydrofolate as cofactor. Inhibitors of TS represent potential... 

In 1967 Santi prepared (313) as an analogue of (305), a proposed intermediate in the TS-mediated conversion of 2 -deoxyuridine-5 -monophosphate... 

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. 

In the 1990s, it was found that tylophorine alkaloids inhibit several key targets for clinically important anticancer drugs, including the metabolic enzymes thymidylate synthase (TS) and dihydrofolate reductase [8, 94], TS catalyzes the reductive methylation of the substrate dUMP (2 -deoxyuridine 5 -monophosphate) to dTMP (2 -deoxythymidine 5 -monophosphate thymidylate) with concomitant conversion of the cofactor CH2THF (5,10-methylenetetrahydrofolate) to DHF (7,8-dihydrofolate) (see Equation 1). 

Folate (foUc acid) is an essential vitamin which, in its active form of tetrahydrofolate (THF, Figure 4-1), transfers 1-carbon groups to intermediates in metaboUsm. Folate plays an important role in DNA synthesis. It is required for the de novo synthesis of purines and for the conversion of deoxyuridine 5-monophosphate (dUMP) to deoxythymidine 5 -monophosphate (dTMP). Additionally, folate derivatives participate in the biosynthesis of choline, serine, glycine, and methionine. However, in situations of folate deficiency, symptoms are not observed from the lack of these products as adequate levels of chohne and amino acids are obtained from the diet. (See also Case 3.)... 

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