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Purine nucleoside phosphorylase (PNP) from Aeromonas hydrophila encoded by the deoD gene has been over-expressed in Escherichia coli, purified, characterized about its substrate specificity and used for the preparative synthesis of some 6-substituted purine-9-ribosides. Substrate specificity towards natural nucleosides showed that this PNP catalyzes the phosphorolysis of both 6-oxo- and 6-aminopurine (deoxy)ribonucleosides. A library of nucleoside analogues was synthesized and then submitted to enzymatic phosphorolysis as well. This assay revealed that 1-, 2-, 6- and 7-modified nucleosides are accepted as substrates, whereas 8-substituted nucleosides are not. A few transglycosylation reactions were carried out using 7-methylguanosine iodide (4) as a d-ribose donor and 6-substituted purines as acceptor. In particular, following this approach, 2- amino-6-chloropurine-9-riboside (2c), 6-methoxypurine- 9-riboside (2d) and 2-amino-6-(methylthio)purine- 9-riboside (2g) were synthesized in very high yield and purity.

The use of nucleoside 2′-deoxyribosyltransferases (NDTs) as biocatalysts for the industrial synthesis of nucleoside analogues is often hindered by their strict preference for 2′-deoxyribonucleosides. It is shown herein that a highly versatile purine NDT from Trypanosoma brucei (TbPDT) can also accept ribonucleosides as substrates; this is most likely because of the distinct role played by Asn53 at a position that is usually occupied by Asp in other NDTs. Moreover, this unusual activity was improved about threefold by introducing a single amino acid replacement at position 5, following a structure-guided approach. Biophysical and biochemical characterization revealed that the TbPDTY5F variant is a homodimer that displays maximum activity at 50 °C and pH 6.5 and shows a remarkably high melting temperature of 69 °C. Substrate specificity studies demonstrate that 6-oxopurine ribonucleosides are the best donors (inosine>guanosine?adenosine), whereas no significant preferences exist between 6-aminopurines and 6-oxopurines as base acceptors. In contrast, no transferase activity could be detected on xanthine and 7-deazapurines. TbPDTY5F was successfully employed in the synthesis of a wide range of modified ribonucleosides containing different purine analogues.

The use of enzymes for the synthesis of nucleoside analogues offers several advantages over multistep chemical methods, including chemo-, regio- and stereoselectivity as well as milder reaction conditions. Herein, the production, characterization and utilization of a purine nucleoside 2’-deoxyribosyltransferase (PDT) from Trypanosoma brucei are reported. TbPDT is a dimer which displays not only excellent activity and stability over a broad range of temperatures (50–70 °C), pH (4–7) and ionic strength (0–500 mM NaCl) but also an unusual high stability under alkaline conditions (pH 8–10). TbPDT is shown to be proficient in the biosynthesis of numerous therapeutic nucleosides, including didanosine, vidarabine, cladribine, fludarabine and nelarabine. The structure-guided replacement of Val11 with either Ala or Ser resulted in variants with 2.8-fold greater activity. TbPDT was also covalently immobilized on glutaraldehyde-activated magnetic microspheres. MTbPDT3 was selected as the best derivative (4200 IU/g, activity recovery of 22 %), and could be easily recaptured and recycled for >25 reactions with negligible loss of activity. Finally, MTbPDT3 was successfully employed in the expedient synthesis of several nucleoside analogues. Taken together, our results support the notion that TbPDT has good potential as an industrial biocatalyst for the synthesis of a wide range of therapeutic nucleosides through an efficient and environmentally friendly methodology.

Impressive antitumor activity has been observed with fludarabine phosphate against tumors that express Escherichia coli purine nucleoside phosphorylase (PNP) due to the liberation of 2-fluoroadenine in the tumor tissue. 6-Methylpurine (MeP) is another cyt

New, improved methods to access nucleosides are of general interest not only to organic chemists but to the greater scientific community as a whole due their key implications in life and disease. Current synthetic methods involve multistep procedures employing protected sugars in the glycosylation of nucleobases. Using modified Mitsunobu conditions, we report on the first direct glycosylation of purine and pyrimidine nucleobases with unprotected d-ribose to provide β-pyranosyl nucleosides and a one-pot strategy to yield β-furanosides from the heterocycle and 5-O-monoprotected d-ribose.

A series of C-6 alkyl, cycloalkyl, and aryl-9-(β-d-ribofuranosyl) purines were synthesized and their substrate activities with Escherichia coli purine nucleoside phosphorylase (E. coli PNP) were evaluated. (Ph 3P)4Pd-mediated cross-c

L-Dopa, the standard therapeutic for Parkinson's disease, is inactivated by the enzyme catechol-O-methyltransferase (COMT). COMT catalyzes the transfer of an activated methyl group from S-adenosylmethionine (SAM) to its catechol substrates, such as L-dopa, in the presence of magnesium ions. The molecular recognition properties of the SAM-binding site of COMT have been investigated only sparsely. Here, we explore this site by structural alterations of the adenine moiety of bisubstrate inhibitors. The molecular recognition of adenine is of special interest due to the great abundance and importance of this nucleobase in biological systems. Novel bisubstrate inhibitors with adenine replacements were developed by structure-based design and synthesized using a nucleosidation protocol introduced by Vorbrueggen and co-workers. Key interactions of the adenine moiety with COMT were measured with a radiochemical assay. Several bisubstrate inhibitors, most notably the adenine replacements thiopyridine, purine, N-methyladenine, and 6-methylpurine, displayed nanomolar IC50 values (median inhibitory concentration) for COMT down to 6 nM. A series of six cocrystal structures of the bisubstrate inhibitors in ternary complexes with COMT and Mg2+ confirm our predicted binding mode of the adenine replacements. The cocrystal structure of an inhibitor bearing no nucleobase can be regarded as an intermediate along the reaction coordinate of bisubstrate inhibitor binding to COMT. Our studies show that solvation varies with the type of adenine replacement, whereas among the adenine derivatives, the nitrogen atom at position 1 is essential for high affinity, while the exocyclic amino group is most efficiently substituted by a methyl group. Copyright

A novel series of 6-methylpurine nucleoside derivatives with substitutions at 5′-position have been synthesised. These compounds bear a 5′-heterocycle such as triazole or a imidazole with a two carbon chain, and an ether, thio ether or amine. To extend the SAR study of 2-fluoroadenine and 6-methyl purine nucleosides, their corresponding α-linker nucleosides with L-xylose and L-lyxose were also synthesized. All of these compounds have been evaluated for their substrate activity with E. coli PNP. Copyright Taylor & Francis, Inc.

6-Methylpurine-β-D-riboside (β-D-MPR) has been synthesized by coupling 6-methylpurine and 1-O-acety1-2,3,5-tri-O-benzoyl-D-ribose using conditions that produce the β-D-anomer exclusively. The in vitro antitumor effects of β-D-MPR and 6-methyl-purine-α-D-riboside (α-D-MPR) in five human tumor cell lines showed that β-D-MPR was highly active (IC50 values ranging from 6 to 34 nM). a-D-MPR, although less active than β-D-MPR, also exhibited significant antitumor effects (IC50 values ranging from 1.47 to 4.83 μM).

A host cell stably transformed or transfected by a vector including a DNA sequence encoding for mutant purine nucleoside cleavage enzymes is provided. The transformed or transfected host cell can be used in combination with a purine substrate to treat tum

The present invention provides a procaryotic host cell stably transformed or transfected by a vector including a DNA sequence encoding for mutant purine nucleoside phosphorylase or hydrolase. The transformed or transfected procaryotic host cell can be used in combination with a purine substrate to treat tumor cells and/or virally infected cells. The present invention provides nucleotide sequences encoding mutant E. coli derived purine nucleoside phosphorylase proteins which can be used in conjunction with an appropriate substrate to produce toxins which impair abnormal cell growth. The invention provides for delivery of the toxin by generation within target cells or by administration and delivery to the cells from without.

The present invention provides nucleoside compounds and certain derivatives thereof which are inhibitors of RNA-dependent RNA viral polymerase. These compounds are inhibitors of RNA-dependent RNA viral replication and are useful for the treatment of RNA-dependent RNA viral infection. They are particularly useful as inhibitors of hepatitis C virus (HCV) NS5B polymerase, as inhibitors of HCV replication, and/or for the treatment of hepatitis C infection. The invention also describes pharmaceutical compositions containing such nucleoside compounds alone or in combination with other agents active against RNA-dependent RNA viral infection, in particular HCV infection. Also disclosed are methods of inhibiting RNA-dependent RNA polymerase, inhibiting RNA-dependent RNA viral replication, and/or treating RNA-dependent RNA viral infection with the nucleoside compounds of the present invention.

Reactions of some 6-substituted 9-(β-D-ribofuranosyl)purines with aqueous sodium hydroxide have been studied by liquid chromatography.The main reaction pathway for the decomposition of 6-chloro, 6-methyl and 6-methylthio derivatives has been shown to consist of three consecutive reactions: an attack of hydroxide ion on C8 atom with rapid subsequent openingof the imidazole ring and anomerization of the glycone moiety, deformylation of the resulting 5-formamido-4-ribosylaminopyrimidines, and clevage of the N-glicosidic bond.With the 6-chloro derivative, the first step is irreversible, while with the 6-methyl and 6-methylthio derivatives, recyclization to purine ribosides competes with the deformylation of 5-formamido-4-ribosylaminopyrimidines. 6-Chloro- and 6-methylthio-9-(β-D-ribofuranosyl)purines also yield some inosine, but this reaction is of minor importance.In contrast, 6-methoxy-9-(β-D-ribofuranosyl)purine is converted quantitatively to inosine.The rate constants for the different partial reactions have been determined at several concentrations of hydroxide ion.The kinetic data, and those reported earlier for adenosine and 9-(β-D-ribofuranosyl)purine, have been used to evaluate the susceptibility of the consecutive steps to the polar nature of the 6-substituent.

A stereoselective photoaddition of methanol to nebularine and 2',3',5'-tri-O-acetylnebularine was investigated.The absolute stereochemistry of the nebularine-methanol photoadduct (2a), a potential transition-state analog of adenosine deaminase, was determined to be 6(S) by X-ray analysis.The addition site of methanol on the purine ring was also chemically demonstrated to be at C(6).Keywords - photoaddition; nebularine; triacetylnebularine; transition-state analog; X-ray analysis; adenosine deaminase; enzyme inhibitor; coformycin; isocoformycin

Treatment of 6-methylsulfonyl-9-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)purine with ethyl acetoacetate and sodium hydride in tetrahydrofuran afforded, after deblocking, 6-ethoxycarbonylmethyl-9-β-D-ribofuranosylpurine.Similarly, replacement of the 6-methylsulfonyl moiety with other carbanions derived from diethyl malonate, ethyl cyanoacetate, malononitrile, nitromethane, and sodium cyanide gave the corresponding 6-C-substituted purine nucleosides.Most of these derivatives exist as the 6-(1H)-exomethylene tautomeric forms. 6-Ethoxycarbonylmethylpurine riboside was further converted to 6-methyl, ethyl, propyl, butyl, and pentyl-purine ribosides by decarboxylation or prior alkylation of the methylene group followed by de-carboxylation.This reaction sequence facilitated the preparation of hitherto almost inaccessible alkyl or C-substituted purine nucleosides.Keywords- nucleophilic aromatic substitution; carbon nucleophiles; purine nucleosides; UV; NMR; tautomerism