New trends in synthesis of pyrazole nucleosides as new antimetabolites

Pyrazole nucleosides and condensed pyrazole nucleosides exhibit various biological activities. This article describes recent synthetic approaches to their preparation, chemical properties, biological activities, and structure-activity relationships, with emphasis to selected drugs or drug candidates. Two pyrazole C-nucleoside compounds pyrazofurin (pyrazomycin) and its alpha-epimer pyrazofurin B are active components of potent antivirals approved for therapeutic use in human medicine aimed against various diseases caused by DNA viruses.     

Recent Updates in Curcumin Pyrazole and Isoxazole Derivatives: Synthesis and Biological Application

Curcumin is an admired, plant‐derived compound that has been extensively investigated for diverse range of biological activities, but the use of this polyphenol is limited due to its instability. Chemical modifications in curcumin are reported to seize this limitation; such efforts are intensively performed to discover molecules with similar but improved stability and better properties. Focal points of these reviews are synthesis of stable pyrazole and isoxazole analogs of curcumin and application in various biological systems. This review aims to emphasize the latest evidence of curcumin pyrazole analogs as a privileged scaffold in medicinal chemistry. Manifold features of curcumin pyrazole analogs will be summarized herein, including the synthesis of novel curcumin pyrazole analogs and the evaluation of their biological properties. This review is expected to be a complete, trustworthy and critical review of the curcumin pyrazole analogs template to the medicinal chemistry community.     

Metabolism of pyrimidine bases and nucleosides by pyrimidine-nucleoside phosphorylases in cultured human lymphoid cells

The anabolism of pyrimidine ribo- and deoxyribonucleosides from uracil and thymine was investigated in phytohemagglutinin-stimulated human peripheral blood lymphocytes and in a Burkitt's lymphoma-derived cell line (Raji). We studied the ability of these cells to synthesize pyrimidine nucleosides by ribo- and deoxyribosyl transfer between pyrimidine bases or nucleosides and the purine nucleosides inosine and deoxyinosine as donors of ribose 1-phosphate and deoxyribose 1-phosphate, respectively: these reactions involve the activities of purine-nucleoside phosphorylase, and of the two pyrimidine-nucleoside phosphorylases (uridine phosphorylase and thymidine phosphorylase). The ability of the cells to synthesize uridine was estimated from their ability to grow on uridine precursors in the presence of an inhibitor of pyrimidine de novo synthesis (pyrazofurin). Their ability to synthesize thymidine and deoxyuridine was estimated from the inhibition of the incorporation of radiolabelled thymidine in cells cultured in the presence of unlabelled precursors. In addition to these studies on intact cells, we determined the activities of purine- and pyrimidine-nucleoside phosphorylases in cell extracts. Our results show that Raji cells efficiently metabolize preformed uridine, deoxyuridine and thymidine, are unable to salvage pyrimidine bases, and possess a low uridine phosphorylase activity and markedly decreased (about 1% of peripheral blood lymphocytes) thymidine phosphorylase activity. Lymphocytes have higher pyrimidine-nucleoside phosphorylases activities, they can synthesize deoxyuridine and thymidine from bases, but at high an non-physiological concentrations of precursors. Neither type of cell is able to salvage uracil into uridine. These results suggest that pyrimidine-nucleoside phosphorylases have a catabolic, rather than an anabolic, role in human lymphoid cells. The facts that, compared to peripheral blood lymphocytes, lymphoblasts possess decreased pyrimidine-nucleoside phosphorylases activities, and, on the other hand, more efficiently salvage pyrimidine nucleosides, are consistent with a greater need of these rapidly proliferating cells for pyrimidine nucleotides.     

Design, synthesis, and evaluation of 3,4-disubstituted pyrazole analogues as anti-tumor CDK inhibitors

Two series of 3,4-disubstituted pyrazole analogues, 3-(benzimidazol-2-yl)-4-[2-(pyridin-3-yl)-vinyl]-pyrazoles (2) and 3-(imidazol-2-yl)-4-[2-(pyridin-3-yl)-vinyl]-pyrazoles (3), were synthesized as novel cyclin-dependent kinase (CDK) inhibitors. Representative compounds showed potent and selective CDK inhibitory activities and inhibited in vitro cellular proliferation in various human tumor cells. The design, synthesis, and preliminary biological evaluation of these pyrazole compounds are reported.     

Design,Synthesis and Biological Activities of New Pyrazole Derivatives Possessing Both Coxib and Combretastatins Pharmacophores

In our efforts to discover novel multi‐target agents having better antitumor activities than celecoxib, 21 new aryl‐substituted pyrazole derivatives possessing cis‐diphenylethylene scaffold were mostly synthesized by a one‐pot approach to ethyl 1,4,5‐triaryl‐1H‐pyrazole‐3‐carboxylates via an improved Claisen condensation – Knorr reaction sequence. The cytotoxic effects of these compounds against three human cancer cell lines HT‐29, Hep‐G2, MCF‐7 as well as their inhibition of NO production were studied. Results showed that incorporation of the important pharmacophoric groups of two original molecules celecoxib and combretastatin A‐4 in a single molecule plays an important role in determining a better biological activities of the new coxib‐hybrided compounds.     

Ring Opening Reaction of Pyrazolo[3,4-c]Maleimide Nucleosides

Abstract

Synthesis of pyrazolo[3,4-c]maleimide nucleosides was attempted, but ring opening reaction of the maleimide part was observed during ammonolysis of sugar-protected pyrazolo[3,4-c]maleimide nucleosides. The isolated pyrazole nucleosides were characterized by NMR spectra and X-ray analysis.     

Cytidine deaminase levels in cultured mammalian cell lines measured by the growth tests and enzyme assays

We developed a test medium for cytidine deaminase in order to examine the distribution of this enzyme in cultured cell lines. The growth of various mammalian cell lines was tested in culture medium containing 2 microM pyrazofurin and 100 microM cytidine. Enzymological assays for the enzyme also were made spectrophotometrically with cell extracts. A good correlation was found between results of cell growth tests and the levels of enzyme activity. Twelve of twenty cell lines were killed in the test medium, but the remaining lines showed good growth. The levels of enzyme activities were lower in the former lines than in the latter. The critical level of enzyme activity required to support cell growth was approximately 30 units per mg protein. These findings indicate that culture medium containing 2 microM pyrazofurin and 100 microM cytidine serves as a test medium for cytidine deaminase. The possibility that the cytidine deaminase may be useful in determining the embryonic origin of cultured cell lines is discussed, based on the growth properties of various cultured cell lines in the test medium.     

Synthesis and biological evaluation of 2',4'- and 3',4'-bridged nucleoside analogues

Most nucleosides in solution typically exist in equilibrium between two major sugar pucker forms, N-type and S-type, but bridged nucleosides can be locked into one of these conformations depending on their specific structure. While many groups have researched these bridged nucleosides for the purpose of determining their binding affinity for antisense applications, we opted to look into the potential for biological activity within these conformationally-locked structures. A small library of 2',4'- and 3',4'-bridged nucleoside analogues was synthesized, including a novel 3',4'-carbocyclic bridged system. The synthesized compounds were tested for antibacterial, antitumor, and antiviral activities, leading to the identification of nucleosides possessing such biological activities. To the best of our knowledge, these biologically active compounds represent the first example of 2',4'-bridged nucleosides to demonstrate such properties. The most potent compound, nucleoside 33, exhibited significant antiviral activity against pseudoviruses SF162 (IC(50)=7.0 μM) and HxB2 (IC(50)=2.4 μM). These findings render bridged nucleosides as credible leads for drug discovery in the anti-HIV area of research.     

Recent advances in the synthesis of conformationally locked nucleosides and their success in probing the critical question of conformational preferences by their biological targets

The present work describes some recent approaches to the syntheses of three classes of locked-North nucleosides: beta-D-ribo-, beta-D-deoxyribo-, and beta-D-dideoxyribonucleosides. The method developed for the latter class permitted access to a novel bicyclo[3.1.0]hexene-type nucleosides structurally similar to D4T and carbovir. A structural analysis and biological activities are discussed.     

The Ugi reaction in the generation of new nucleosides as potential antiviral and antileishmanial agents

5-Formyl-2'-deoxyuridine-3',5'-diacetate was converted to a small library of 5-substituted pyrimidine nucleoside N-acylamino acid amides by means of a Ugi multicomponent reaction. The reaction allowed introduction of various substituents at the acyl moiety, at the amino acid alpha-amide group, and at the amino acid carboxyl function. Evaluation of these novel 5-substituted nucleosides against vaccinia virus and cowpox virus provided one compound with discernable activity against cowpox virus but five- to eightfold less active than the Cidofovir standard. More promising activity was seen for the inhibition of Leishmania donovani promastigotes. Several synthetic products showed antileishmanial activity in the 10(-5)M range. When compared to earlier studies demonstrating anti-orthopoxviral and antileishmanial activity of 5-substituted pyrimidine nucleosides, these results imply that the 5-(N-acylamino acid amide)-derivatized pyrimidine nucleosides may possess more steric bulk, greater hydrophobicity, and more flexibility than is compatible with these particular biological activities.     

Synthesis of 4'-substituted nucleosides and their biological evaluation.

4'-C-Ethynyl-beta-D-arabino- and 4'-C-ethynyl-beta-D-2'-deoxy-ribo-pentofuranosyl pyrimidines were synthesized. Most of these 4'-ethynyl nucleosides showed interesting biological activities.     

Structural determinants for the inhibitory ligands of orotidine-5′-monophosphate decarboxylase

In recent years, orotidine-5′-monophosphate decarboxylase (ODCase) has gained renewed attention as a drug target. As a part of continuing efforts to design novel inhibitors of ODCase, we undertook a comprehensive study of potent, structurally diverse ligands of ODCase and analyzed their structural interactions in the active site of ODCase. These ligands comprise of pyrazole or pyrimidine nucleotides including the mononucleotide derivatives of pyrazofurin, barbiturate ribonucleoside, and 5-cyanouridine, as well as, in a computational approach, 1,4-dihydropyridine-based non-nucleoside inhibitors such as nifedipine and nimodipine. All these ligands bind in the active site of ODCase exhibiting distinct interactions paving the way to design novel inhibitors against this interesting enzyme. We propose an empirical model for the ligand structure for rational modifications in new drug design and potentially new lead structures.     

Increased levels of UMP synthase protein and mRNA in pyrazofurin-resistant rat hepatoma cells

Rat hepatoma cells that have undergone stepwise selection in increasing concentrations of pyrazofurin have coordinately increased levels of both orotate phosphoribosyltransferase (EC 2.4.2.10) and orotidine-5'-phosphate decarboxylase (EC 4.1.1.23) activity. These two activities catalyze the conversion of orotic acid to UMP in de novo pyrimidine biosynthesis. Cells selected in 50 microM pyrazofurin have over 40 times the wild type level for both activities. A single polypeptide of approximately 55,000 daltons is increased in the resistant cells in amounts corresponding to the increase in the two activities. Resistant cell lines that are grown for extended periods in the absence of pyrazofurin are unstable, losing their elevated levels of both enzyme activities and the increased specific protein. Antibody prepared against a purified protein containing both enzyme activities binds specifically to this increased protein. These results corroborate other evidence indicating the two enzyme activities are contained within a single polypeptide called UMP synthase. Poly(A+) mRNA isolated from wild type and resistant lines was analyzed by in vitro translation for production of UMP synthase protein. Immunoprecipitation of the translation products shows the resistant cells have a 17-fold increase in translatable mRNA activity coding for UMP synthase. The synthase accounts for 0.24% of the total in vitro translation products synthesized with poly(A+) mRNA from the pyrazofurin-resistant cells as opposed to 0.014% with wild type mRNA. A cloned UMP synthase cDNA sequence hybridizes strongly to a 1.8-kilobase mRNA in the resistant cells. This mRNA is only barely detectable in equivalent preparations from wild type cells. Quantitation of the mRNA by dot hybridization techniques indicates a 16-fold increase in UMP synthase mRNA in the resistant cells. Although this increase in mRNA for UMP synthase could explain most of the increased protein, it is not sufficient to totally account for the 40-fold increase in UMP synthase.     

Nucleosides,XLIV1 Synthesis,Properties and Biological Activity of Indazole Nucleosides

Abstract

Various new haloindazole-1-β-D-ribofuranosides (10-17,20,21) and a 2-β-D-ribofuranoside (18) have been synthesized by the fusion method and by direct halogenations, respectively. The new nucleosides have been characterized by UV and ¹H NMR spectra as well as pK_a determinations. Indazole ribofuranosides behave in aqueous acid like purine and benzimidazole nucleosides showing the same mechanism of cleavage of the glycosidic bonds. Toxicity studies against various cell populations indicate only little biological activities.     

Pyrimidine as constituent of natural biologically active compounds

This review describes the various manifestations of the pyrimidine system (alkylated, glycosylated, benzo-annelated.). These comprise pyrimidine nucleosides as well as alkaloids and antibiotics--some of them have been discovered and isolated from natural sources already long time ago, others have been reported very recently. A short overview on pyrimidine syntheses (prebiotic synthesis, biosynthesis, and metabolism) is given. The biological activities of most of the pyrimidine analogs are briefly described, and, in some cases, syntheses are formulated.     

Synthesis of 2-(3'-azido- and 3'-amino-3'-deoxy-beta-D-ribofuranosyl)thiazole-4-carboxamide

In view of biological activities of tiazofurin and azido or aminosugar nucleosides, novel azido- and amino-substituted tiazofurin derivatives (1 and 2) were efficiently synthesized starting from 1,2;5,6-di-O-isopropylidene-D-glucose.     

Synthesis and biological evaluation of novel apio nucleosides with thiazole-4-carboxamide and 1,2,4-triazole-3-carboxamide

In view of biological activities of azole nucleosides and apio-dideoxynucleoside, novel apio nucleoside analogues (1 and 2) with thiazole and triazole base moiety were synthesized using 2,3-O-isopropylidene-apio-beta-D-furanose (3), which was prepared from D-mannose.     

Synthesis and DNA topoisomerase-II inhibitory activity of unnatural nucleosides

The synthesis and biological activities of a number of unnatural nucleosides (23-43) is described. Nucleosides have been synthesized by SnCl4-catalyzed condensation of amino sugar acetates and silylated modified pyrimidines. Few of the 2'-O-acetyl derivatives of the nucleosides were hydrolyzed to the respective hydroxy derivatives by treatment with methanol saturated with ammonia. The compounds were screened against Filarial DNA-topoisomerase-II but only one of the compounds (29) inhibited this enzyme at 40 microg/mL of reaction mixture.     

The stilbene derivatives,nucleosides, and nucleosides modified by stilbene derivatives

In this short review, including 187 references, the issues of biological activity of stilbene derivatives and nucleosides and the biological and medicinal potential of fusion of these two classes are discussed. The stilbenes, especially the stilbenoids, and nucleosides are both biologically active. Hybrids formed from binding of these compounds have not yet been broadly studied. However, those that have been investigated exhibit desirable medicinal properties. The review is divided in such parts: I. Derivative of stilbene (biomedical investigations, biological activities in cells, enzymes and hazard), parts II. naturally occurred nucleoside and its derivatives: uridine, thymidine and 5-methyluridine, cytidine, adenosine, guanosine and part III. hybrid molecules- drugs and hybrid molecules- nucleoside - stilbene and its derivative.     

Coordinate overproduction of orotate phosphoribosyltransferase and orotidine-5'-phosphate decarboxylase in hamster cells resistant to pyrazofurin and 6-azauridine.

Cells resistant to pyrazofurin and 6-azauridine have been selected from a simian virus 40-transformed Syrian hamster line and from a Chinese hamster lung line. By increasing the concentrations of inhibitors in several steps, mutant cells from both lines have been obtained which resist high concentrations (1 to 5 mM) of the two inhibitors separately or together. Orotidine-5'-phosphate decarboxylase (EC 4.1.1.23), the sixth and last enzyme in UMP biosynthesis, is inhibited by the nucleoside monophosphates derived from pyrazofurin or 6-azauridine. The activity of this enzyme is increased in each resistant cell line tested. Furthermore, there is a parallel increase in each case in the activity of the fifth enzyme of the pathway, orotate phosphoribosyltransferase (EC 2.4.2.10), which is not inhibited by pyrazofurin or 6-azauridine monophosphates, and the amount of increase is up to 67 times the level found in wild type cells. In contrast, the activities of the first three enzymes of UMP biosynthesis remain essentially unchanged in the mutants. Resistant Chinese hamster cells remain sensitive to 5-fluorouridine; this indicates that uridine kinase, the enzyme necessary to convert 6-azauridine to the monophosphate, is still functional.