Glycinamide ribonucleotide

Pemetrexed is chemically similar to folic acid. It inhibits three enzymes used in purine and pyrimidine synthesis - thymidylate synthetase, dihydrofolate reductase, and glycinamide ribonucleotide formyl transferase. By inhibiting the formation of precursor purine and pyrimidine nucleotides, pemetrexed prevents the formation of DNA and RNA. In 2004 it was approved for treatment of malignant pleural mesothelioma and as a second-line agent for the treatment of non-small cell lung cancer. Adverse effects include gastrointestinal complaints, bone marrow suppression, alopecia, allergic and neurotoxic reactions. 

Glycinamide ribonucleotide transformylase (GAR Tfase) is a folate-dependent enzyme essential to the de novo purine biosynthetic pathway. It utilizes the cofactor 10-formyl tetrahydrofohc acid (10-formyl-THF) to transfer a formyl group to the primary amine of its substrate a-glycinamide ribonucleotide. Potent, and potentially selective, inhibitors of GARTfase and de novo purine biosynthesis have been shown to be promising as antitumor drugs. 

The dual alkylation/S Ar cyclization of A 1,A z-bis(2,4-dimethoxybenzyl)ethane-l,2-diamine (bis-DMB-ethylene-diamine) with the chloromethyl pyrimidine 102 provided the fused ring diazepine 103, a transformation that could not be accomplished by simply using unprotected ethylenediamine (Scheme 56). The product is an intermediate toward the synthesis of potential folate-related antitumor agents that act as glycinamide ribonucleotide formyltrans-ferase inhibitors <2004HC0405>. 

Directly coupled HPLC-NMR spectroscopy has been used in a number of other studies of chemical impurities. An impurity in a bulk drug sample of the glycinamide ribonucleotide transformylase inhibitor AG2034, shown below ... 

Fig. 11.6. Interconversions of tetrahydrofolate derivatives. FH2 = dihydrofolic acid FH4 = tetrahydrofolic acid AICAR -= 5 aminoimidazole 4-carboxamide ribonucleotide FAICAR = formyl AICAR GAR = glycinamide ribonucleotide FGAR = formyl GAR Glu = glutamic acid FIGLU = formimino glutamic acid. (Modified from Mudd and Cantoni, 1964.)...

Fig. 13.2. Synthesis of IMP. c = Hypoxanthine phosphoribosyl transferase (HPRT) GAR = glycinamide ribonucleotide FGAR = formyl glycinamide ribonucleotide PRPP = phosphoribosyl pyrophosphate AICAR = 5 aminoimidazole-4-carboxamide...

Fig. 4. (a) Sequence alignment of the E. coli genes for glycinamide ribonucleotide... 

Aimi,J., Qiu, H., Williams, J., Zalkin, H., and Dixon, J. E. (1990). De novo purine nucleotide biosynthesis cloning of human and avian cDNAs encoding the trifunctional glycinam-ide ribonucleotide synthetase-aminoimidazole ribonucleotide synthetase-glycinamide ribonucleotide transformylase by functional complementation in E. colt. Nucleic Acids Res., 18, 6665-6672. 

Schmitt, E., Blanquet, S., and Mechulam, Y. (1996). Structure of crystalline Escherichia colt methionyl-tRNA(f)Met formyltransferase comparison with glycinamide ribonucleotide formyltransferase. EMBO J., 15, 4749-4758. 

Wang, W., Kappock, T. J., Stubbe, J., and Ealick, S. E. (1998). X-ray crystal structure of glycinamide ribonucleotide synthetase from Escherichia coli. Biochemistry, 37, 15647-15662. 

Faessel HM, Slocum HK, Rustum YM, Greco WR. 1999. Folic acid-enhanced synergy for the combination of trimetrexate plus the glycinamide ribonucleotide formyltransferase inhibitor 4-[2-(2-amino-4-oxo-4,6,7,8-tetrahydro-3H-pyrimidino[5,4,6][l,4]thiazin-6-yl)-(S)-ethyl]-2,5-thienoyl amino-L-glutamic acid (AG2034)—comparison across sensitive and resistant human tumor cell lines. Biochem Pharmacol 57 567-577. 

Fig. 9.8. a) Structural overlay of glycinamide ribonucleotide transformylase (PurN) [155] and the N-terminal domain of tRNA(fMet)-formyl-transferase (FMT) [156] from E. coli. Despite the low sequence identity (33 %), the two structures are almost perfectly superimposable. b) Structure-based multiple sequence alignment of PurN... 

In the enzyme catalysis of the first committed step in the de novo synthesis of purines, an amino group from L-glutamine is transferred to 5-phosphoribosyl-l-pyrophosphate to form glutamate and 5-phosphoribosyl-1-amine. The assay includes glycinamide ribonucleotide synthetase, which converts 5-phosphoribosyl-l-amine to glycinamide ribonucleotide, which is the reaction product quantitated. 

Glycinamide ribonucleotide transformy-lase (GAR TFase) catalyzes the transfer of a formyl group from JV -formyltetrahydrofo-late to glycinamide ribonucleotide (Equation 17.37). This is a crucial step in de novo purine biosynthesis, which is essential for cell division, and GAR TFase has become a target enzyme for the development of antineoplastic agents. 

The same but not the same. Write out mechanisms for the conversion of phosphoribosylamine into glycinamide ribonucleotide and of xanthylate into guanylate. 

J.B. Thoden, S. Firestine, A. Nixon, S. J. Benkovic, and H.M. Holden. 2000. Molecular structure of Escherichia coli PurT-encoded glycinamide ribonucleotide transformylase Biochemistry 39 8791-8802. (PubMed)... 

The purine biosynthetic pathway requires 10-formyl-H4folate. 5,10-Methylene-Hifolate is oxidized to 5,10-methenyl-H4folate, as shown in Figure 9.6. 5,10-Methenyl-H4folate is then hydrated to produce 10-formyl-H4folate. 10-Formyl-H4folate is used at two steps of the purine biosynthetic pathway, namely for conversion of glycinamide ribonucleotide (GAR) to formyl-GAR and of aminoimi-dazolecarboxamide ribonucleotide (AlCAR) to formyl-AICAR. 

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