Thymidine 5’-monophosphate

Methotrexate (MTX, chemical structure shown in Fig. 1.) competitively inhibits the dehyrofolate reductase, an enzyme that plays an essential role in purine synthesis. The dehydrofolate reductase regenerates reduced folates when thymidine monophosphate is formed from deoxyuridine monophosphate. Without reduced folates cells are unable to synthesize thymine. Administration of N-5 tetrahydrofolate or N-5 formyl-tetrahydrofolate (folinic acid) can bypass this block and rescue cells from methotrexate activity by serving as antidote. 

Posttranslational modification of preformed polynucleotides can generate additional bases such as pseudouridine, in which D-ribose is linked to C-5 of uracil by a carbon-to-carbon bond rather than by a P-N-glycosidic bond. The nucleotide pseudouridylic acid T arises by rearrangement of UMP of a preformed tRNA. Similarly, methylation by S-adenosylmethionine of a UMP of preformed tRNA forms TMP (thymidine monophosphate), which contains ribose rather than de-oxyribose. 

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. 

DHFR has been the object of intense research for the last few decades. The enzyme catalyses the NADPH-dependent reduction of 7,8-dihydrofolate to 5,6,7,8 tetrahydrofolate, a chemical which participates in the thymidilate synthesis cycle. Thus, the enzyme is crucial in the synthesis of thymidine monophosphate as well as in various one-carbon unit transfer reactions. 

We first applied Tethering to thymidylate synthase (TS). This enzyme converts de-oxyuridine monophosphate (dUMP) to thymidine monophosphate (dTMP), an activity essential for DNA synthesis. The cancer drug 5-fluorouracil irreversibly inhibits TS, and a selective inhibitor of a non-human form of the enzyme could yield a new antibiotic or antifungal drug [23]. 

In Fig. 1 various targets of some important cytostatic agents are depicted. Their main mechanisms of action can be briefly summarized as follows. Pentostatin blocks purine nucleotides by inhibiting adenosine deaminase. 6-Mercaptopurine and 6-thioguanine inhibit purine ring biosynthesis and they inhibit nucleotide interconversions. Methotrexate by inhibiting dihydrofolate reduction blocks thymidine monophosphate and purine synthesis. 5-Fluorouracil also blocks thymidine monophosphate synthesis. Dactinomycin, daunorubicin, doxorubicin and mitoxantrone intercalate with DNA and inhibit RNA synthesis. L-asparaginase deaminates... 

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). 

Kielley, R.K. Purification and properties of thymidine monophosphate kinase from mouse hepatoma. J. Biol. Chem., 245, 4204-4212 (1970)... 

Nucleosides and nucleotides, 2 X 10-6 molar solution of adenosine, guanosine, cytidine, uridine, thymidine, inosine, adenosine monophosphate, adenosine triphosphate, guanosine monophosphate, uridine monophosphate, thymidine monophosphate, inosine monophosphate. 

Since DNA contains thymine (5-methyluracil) as a major base instead of uracil, the synthesis of thymidine monophosphate (dTMP, or thymidylate) is essential to provide dTTP (thymidine triphosphate), which is needed for DNA replication together with dATP, dGTP, and dCTP. 

Grachev SA, Kropachev EV, Litvyakova Gl (1983) Synthesis of 5-S-cysteamine-6-hydroxythymine and evidence of its formation in the y radiolysis of aqueous solutions of thymine and cyste-amine. Bull Acad Sci USSR, Chem Ser (Engl Trans) 1595-1600 Grachev SA, Kropachev EV, Litvyakova Gl (1986) Addition of cysteamine to thymine and thymidine monophosphate initiated by y-irradiation. Bull Acad Sci USSR, Chem Ser (Engl Trans) 10 2178-2184... 

THYMIDINE KINASE (TK) An enzyme involved in the utilization of the nucleoside thymidine (which ultimately becomes part of the structure of DNA) catalyzes the phosphorylation of thymidine to thymidine monophosphate mutants that lack TK are resistant to the toxic effects of several thymidine analogues, including bromodeoxy-uridine and trifluorothymidine selection of these drug-resistant mutants provides the basis of several... 

ADP adenosine diphosphate, ANP atrial natriuretic peptide, AP5DTPT(5 -adenosyl)P5-(5 -thymidyl)pentaphosphate, ATP adenosine triphosphate, AZTMP 3 -azido-3 -deoxythymidine monophosphate, dGMP deoxyguanosine monophosphate, P 4-(2-hydroxyethyl)-l-piperazine ethanesulfonic acid, HMD hymenialdisine, TMP thymidine monophosphate... 

Deoxythymidine monophosphate derivatives that inhibit thymidine monophosphate kinase 36 MFA Alignments performed with least-squares (predictive R2=0.70), pharmacophore (0.56), or docked conformations (0.72). Receptor-based alignment performed best Aparna et al. (42)... 

Thirty 5 -thiourea-substituted a-thymidine analogues used to develop receptor-independent 4D-QSARmodels ( 3 = 0.83) for thymidine monophosphate kinase inhibitors. The model was also put into the context of reported crystallographically characterized inhibitor/enzyme interactions... 

UNITY pharmacophore, FlexXd docking, and structure interaction fingerprint approaches were used to identify compounds in the Maybridge database (59,275 compounds) as potential thymidine monophosphate kinase inhibitors... 

Aparna V, Jeevan J, Ravi M et al (2006) 3D-QSAR studies on antitubercular thymidine monophosphate kinase inhibitors based on different alignment methods. Bioorg Med Chem Lett 16 1014-1020... 

Gopalakrishnan B, Aparna V, Jeevan J et al (2005) A virtual screening approach for thymidine monophosphate kinase inhibitors as... 

Thymine Deoxyribose Thymidine Thymidylic acid thymidine monophosphate (dTMP) Thymidine diphosphate (dTDP) Thymidine triphosphate (dTTP)... 

Kumar A, Sevilla MD (2007). Low-energy electron attachment to 5 -Thymidine monophosphate Modeling single strand breaks through dissociative electron attachment. J Phys Chem B 111 5464-5474. 

Figure 10.8. Synthesis of thymidine monophosphate. Thymidylate synthetase, EC 2.1.1.45 and dihydrofolate rednctase, EC I.5.I.3. THE tetrahydrofolate.

Thymidylate Synthetase and Dihydrofolate Reductase Methylation of deoxyuridine monophosphate (dUMP) to thymidine monophosphate (TMP see Figure 10.8) is essential for the synthesis of DNA, although preformed TMP can be reutUized by salvage from the catabolism of DNA. 

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