2‐Substituted 6‐(Het)aryl‐7‐deazapurine Ribonucleosides: Synthesis,Inhibition of Adenosine Kinases,and Antimycobacterial Activity

A series of 6‐(hetero)aryl‐ or 6‐methyl‐7‐deazapurine ribonucleosides bearing a substituent at position 2 (Cl, F, NH₂, or CH₃) were prepared by cross‐coupling reactions at position 6 and functional group transformations at position 2. Cytostatic, antiviral, and antimicrobial activity assays were performed. The title compounds were observed to be potent and selective inhibitors of Mycobacterium tuberculosis adenosine kinase (ADK), but not human ADK; moreover, they were found to be non‐cytotoxic. The antimycobacterial activities against M. tuberculosis, however, were only moderate. The reason for this could be due to either poor uptake through the cell wall or to parallel biosynthesis of adenosine monophosphate by the salvage pathway.     

Synthesis and Biological Evaluation of Pyrrolo[2,1‐f][1,2,4]triazine C‐Nucleosides with a Ribose, 2′‐Deoxyribose,and 2′,3′‐Dideoxyribose Sugar Moiety

The synthesis of hitherto unknown pyrrolo[2,1‐f][1,2,4]triazine C‐nucleosides is described. Structural variations (chlorine, bromine, iodine, and cyano groups) were introduced at position 7 of 4‐aza‐7,9‐dideazaadenine. In addition, pyrrolo[2,1‐f][1,2,4]triazine C‐nucleosides bearing a 2′‐deoxy‐, 2′,3′‐dideoxy‐, and 2′,3′‐dehydrodideoxyribose moiety were also prepared. Among these analogues, the pyrrolo[2,1‐f][1,2,4]triazine C‐ribonucleosides with either a hydrogen atom or cyano group at position 7 of the nucleobase displayed potent cytotoxic activity in a panel of various cancer cell lines.     

CycloSal‐phosphate Pronucleotides of Cytostatic 6‐(Het)aryl‐7‐deazapurine Ribonucleosides: Synthesis,Cytostatic Activity,and Inhibition of Adenosine Kinases

A series of cycloSal‐phosphate prodrugs of a recently described new class of nucleoside cytostatics (6‐hetaryl‐7‐deazapurine ribonucleosides) was prepared. The corresponding 2′,3′‐isopropylidene 6‐chloro‐7‐deazapurine nucleosides were converted into 5‐O′‐cycloSal‐phosphates. These underwent a series of Stille or Suzuki cross‐couplings with diverse (het)arylstannanes or ‐boronic acids to yield the protected 6‐(het)aryl‐7‐deazapurine pronucleotides that were subsequently deprotected to give 12 derivatives of free pronucleotides. The in vitro cytostatic effect of the pronucleotides was compared with parent nucleoside analogues. In most cases, the activity of the pronucleotide was similar to or somewhat lower than that of the corresponding parent nucleosides, with the exception of 7‐fluoro pronucleotides 13 a , 13 b , and 13 d , which had exhibited GIC₅₀ values that were improved by one order of magnitude (to the low nanomolar range). The presence of a cycloSal‐phosphate group also influenced selectivity toward various cell lines. Several pronucleotides were found which strongly inhibit human adenosine kinase but only weakly inhibit the MTB adenosine kinase.     

Synthesis and Biological Evaluation of Purine 2′‐Fluoro‐2′‐deoxyriboside ProTides as Anti‐influenza Virus Agents

2′‐Fluoro‐2′‐deoxyguanosine has been reported to have potent anti‐influenza virus activity in vitro and in vivo. Herein we describe the synthesis and biological evaluation of 6‐modified 2′‐fluoro‐2′‐deoxyguanosine analogues and their corresponding phosphoramidate ProTides as potential anti‐influenza virus agents. Whereas the parent nucleosides were devoid of antiviral activity in two different cellular assays, the 5′‐O‐naphthyl(methoxy‐L ‐alaninyl) ProTide derivatives of 6‐O‐methyl‐2′‐fluoro‐2′‐deoxyguanosine, 6‐O‐ethyl‐2′‐fluoro‐2′‐deoxyguanosine, and 2′‐deoxy‐2′‐fluoro‐6‐chloroguanosine, and the 5′‐O‐naphthyl(ethoxy‐L ‐alaninyl) ProTide of 6‐O‐ethyl‐2′‐fluoro‐2′‐deoxyguanosine displayed antiviral EC₉₉ values of ～12 μM . The antiviral results are supported by metabolism studies. Rapid conversion into the L ‐alaninyl metabolite and then 6‐modified 2′‐fluoro‐2′‐deoxyguanosine 5′‐monophosphate was observed in enzymatic assays with yeast carboxypeptidase Y or crude cell lysate. Evidence for efficient removal of the 6‐substituent on the guanine part was provided by enzymatic studies with adenosine deaminase, and by molecular modeling of the nucleoside 5′‐monophosphates in the catalytic site of a model of ADAL1, thus indicating the utility of the double prodrug concept.     

Synthetic and Biological Studies of Tubulin Targeting C2‐Substituted 7‐Deazahypoxanthines Derived from Marine Alkaloid Rigidins

C2‐aryl‐ and C2‐alkyl‐7‐deazahypoxanthines as analogues of marine alkaloid rigidins were prepared utilizing novel synthetic methods developed for the construction of the pyrrolo[2,3‐d]pyrimidine ring system. The new compounds exhibited sub‐micromolar to nanomolar antiproliferative potencies against a panel of cell lines including in vitro models for drug‐resistant tumors, such as glioblastoma, melanoma and non‐small‐cell lung cancer. A selected representative C2‐methyl‐7‐deazahypoxanthine was found to inhibit microtubule dynamics in cancer cells, lending evidence for tubulin targeting as a mode of action for these compounds in cancer cells. The results of the docking studies utilizing the colchicine site on β‐tubulin were consistent with the observed structure–activity relationship data, including an important finding that derivatization at C2 with linear alkyl groups leads to the retention of activity, thus permitting the attachment of a biotin‐containing linker for the subsequent proteomics assays. Because many microtubule‐targeting compounds are successfully used to fight cancer in the clinic, the reported antitubulin rigidin analogues have significant potential as new anticancer agents.     

Structure‐Based Design,Synthesis, and Evaluation of 2′‐(2‐Hydroxyethyl)‐2′‐deoxyadenosine and the 5′‐Diphosphate Derivative as Ribonucleotide Reductase Inhibitors

Analysis of the recently solved X‐ray crystal structures of Saccharomyces cerevisiae ribonucleotide reductase I (ScRnr1) in complex with effectors and substrates led to the discovery of a conserved water molecule located at the active site that interacted with the 2′‐hydroxy group of the nucleoside ribose. In this study 2′‐(2‐hydroxyethyl)‐2′‐deoxyadenosine 1 and the 5′‐diphosphate derivative 2 were designed and synthesized to see if the conserved water molecule could be displaced by a hydroxymethylene group, to generate novel RNR inhibitors as potential antitumor agents. Herein we report the synthesis of analogues 1 and 2 , and the co‐crystal structure of adenosine diphosphate analogue 2 bound to ScRnr1, which shows the conserved water molecule is displaced as hypothesized.     

Synthesis and characterization of the soluble fluorescent poly[2‐decyloxy‐5‐(2′‐(6′‐dodecyloxy)naphthyl)‐1,4‐phenylenevinylene]

A new soluble fluorescent polymer, poly[2‐decyloxy‐5‐(2′‐(6′‐dodecyl‐oxy)naphthyl)‐1,4‐phenylenevinylene] (DDN‐PPV), with no tolane‐bisbenzyl (TBB) structure defects is prepared by the dehydrohalogenation of 1,4‐bis(bromomethyl)‐2‐decyloxy‐5‐(2′‐(6′‐dodecyloxy)naphthyl)benzene (as monomer) in this study. The aforementioned monomer is synthesized via such chemical reactions as alkylation, bromination, and Suzuki coupling reactions. The structure and properties of the DDN‐PPV are examined by ¹H NMR, FTIR, UV/vis, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The two asymmetric decyloxy and 6′‐dodecyloxynaphthyl substituents on the phenylene ring make the DDN‐PPV soluble in organic solvents and eliminate the TBB structure defects. With the DDN‐PPV acting as a light‐emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DDN‐PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 538 nm. The turn on voltage of the device is about 16.6 V. Its maximum brightness is 14 cd/m² at a voltage of 18.2 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2734–2741, 2007     

siRNA Modified with 2′‐Deoxy‐2′‐C‐methylpyrimidine Nucleosides

(2′S)‐2′‐Deoxy‐2′‐C‐methyluridine and (2′R)‐2′‐deoxy‐2′‐C‐methyluridine were incorporated in the 3′‐overhang region of the sense and antisense strands and in positions 2 and 5 of the seed region of siRNA duplexes directed against Renilla luciferase, whereas (2′S)‐2′‐deoxy‐2′‐C‐methylcytidine was incorporated in the 6‐position of the seed region of the same constructions. A dual luciferase reporter assay in transfected HeLa cells was used as a model system to measure the IC₅₀ values of 24 different modified duplexes. The best results were obtained by the substitution of one thymidine unit in the antisense 3′‐overhang region by (2′S)‐ or (2′R)‐2′‐deoxy‐2′‐C‐methyluridine, reducing IC₅₀ to half of the value observed for the natural control. The selectivity of the modified siRNA was measured, it being found that modifications in positions 5 and 6 of the seed region had a positive effect on the ON/OFF activity.     

Photoconductivity of 1,2‐(1′,1′,2′,2′‐tetracyanomethanoxymethano)[60]fullerene‐doped PVK

1,2‐(1′,1′,2′,2′‐Tetracyanomethanoxymethano)[60]fullerene, a derivative of C₆₀, is a better electron acceptor than the parent C₆₀. The film of PVK doped with 1.6 wt % of this derivative was prepared and characterized. The micromorphology of the film was studied by transmission electron microscopy (TEM) and high‐resolution transmission electron microscopy (HRTEM). The photoinduced discharge curves and photoconduction spectra of the films were measured. The results showed that PVK doped with the C₆₀ derivative displayed more photoconductivity than that of PVK doped with pure C₆₀ or a mixture of C₆₀ and C₇₀. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 209–213, 1999     

Enantioenriched Calcium‐(R)‐5,5′,6,6′,7,7′,8,8′‐Octahydro‐BINOL (H8‐BINOL): An Efficient Catalyst for the Creation of a Quaternary Stereocenter#

An efficient catalyst for the creation of a quaternary stereocenter has been developed utilizing easily available, eco‐friendly CaCl₂ and applied for enantioselective carbon‐carbon bond forming reactions. Among the surveyed ligands, it was found that (R)‐5,5′,6,6′,7,7′,8,8′‐octahydro‐BINOL‐Ca ( 2f ) gave maximum ee (72%) with excellent yields.     

Crystallography and Structure–Property Relationships in 2,2′,2″,2′′′,4,4′,4″,4′′′,6,6′,6″,6′′′‐Dodecanitro‐1,1′ : 3′1″ : 3″,1′′′‐ Quaterphenyl (DODECA)

X‐ray crystallographic study of 2,2′,2″,2′′′,4,4′,4″,4′′′,6,6′,6″,6′′′‐dodecanitro‐1,1′ : 3′1″ : 3″,1′′′‐quaterphenyl (DODECA) has been carried out. Nonbonding interatomic distances of oxygen atoms inside of all the nitro groups are shorter than those corresponding to the intermolecular contact radii for oxygen. By means of the DFT B3LYP/6‐31(d, p) method a difference of 136 kJ mol⁻¹ between the X‐ray and DFT structures of DODECA was found. The bearer of the highest initiation reactivity in its molecule in solid phase should be the nitro group at 4′′′‐position, in contrast to those at 2′‐ or 2″‐positions in its isolated molecule. The most reactive nitro group in the DODECA molecule can be well specified by the relationship between net charges on nitro groups and charges on their nitrogen atoms, both of them for the X‐ray structure. The ¹⁵N chemical shift, corresponding to this nitro group for the initiation by impact and shock, correlates very well with these shifts of the reaction centers of the other six “genuine” polynitro arenes.     

Synthesis of 3′,4′‐disubstituted terthiophenes. Characterization and electropolymerization. I. 3′,4′‐dibromo‐2,2′:5′,2″‐terthiophene in photovoltaic display

Recent studies on conducting polymers have demonstrated that polymers of 3‐substituted thiophene produce very stable compounds. Although this kind of substitution improves the regularity, structural defects still exist. To overcome this drawback, the polymerization of 3,4‐disubstituted thiophene is proposed as a convenient way of synthesizing regular, highly conjugated conductive polymers. Our interest is thus focused on the synthesis of tetra‐substituted thiophene derivatives, their polymerization, electrochemical properties, spectral characteristics, oxidizing potential, and the feasibility of photocells development. In this article, we report the synthesis and characterization of 3′,4′‐dibromo‐2,2′:5′,2″‐terthiophene which, as such or modified, may be a good starting product for obtaining new monomers of 3′,4′‐disubstituted terthiophenes, that would allow the effect of the substituents on the properties of the respective polymers to be studied. In addition, the monomer was electropolymerized and the resulting deposit was electrochemically and morphologically characterized. Two conclusions were drawn: first, more uniform and homogeneous layers than those of polythiophene are obtained; second, the thin layers of the polymer, electron acceptors, absorb in the visible. Finally, photocells were assembled to investigate their photovoltaic effect. Although the so prepared solar cells showed some photovoltaic effect, the yield was low.© 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5314–5321, 2006     

Synthesis of 3′‐Fluoro‐tRNA Analogues for Exploring Non‐ribosomal Peptide Synthesis in Bacteria

Aminoacyl‐tRNAs (aa‐tRNAs) participate in a vast repertoire of metabolic pathways, including the synthesis of the peptidoglycan network in the cell walls of bacterial pathogens. Synthesis of aminoacyl‐tRNA analogues is critical for further understanding the mechanisms of these reactions. Here we report the semi‐synthesis of 3′‐fluoro analogues of Ala‐tRNA^Ala. The presence of fluorine in the 3′‐position blocks Ala at the 2′‐position by preventing spontaneous migration of the residue between positions 2′ and 3′. NMR analyses showed that substitution of the 3′‐hydroxy group by fluorine in the ribo configuration favours the S‐type conformation of the furanose ring of terminal adenosine A76. In contrast, the N‐type conformation is favoured by the presence of fluorine in the xylo configuration. Thus, introduction of fluorine in the ribo and xylo configurations affects the conformation of the furanose ring in reciprocal ways. These compounds should provide insight into substrate recognition by Fem transferases and the Ala‐tRNA synthetases.     

Synthesis and in vitro Evaluation of West Nile Virus Protease Inhibitors Based on the 2‐{6‐[2‐(5‐Phenyl‐4H‐{1,2,4]triazol‐3‐ylsulfanyl)acetylamino]benzothiazol‐2‐ylsulfanyl}acetamide Scaffold

In recent years, clinical symptoms resulting from West Nile virus (WNV) infection have worsened in severity, with an increased frequency in neuroinvasive diseases among the elderly. As there are presently no successful therapies against WNV for use in humans, continual efforts to develop new chemotherapeutics against this virus are highly desired. The viral NS2B‐NS3 protease is a promising target for viral inhibition due to its importance in viral replication and its unique substrate preference. In this study, a WNV NS2B‐NS3 protease inhibitor with a 2‐{6‐[2‐(5‐phenyl‐4H‐[1,2,4]triazol‐3‐ylsulfanyl)acetylamino]benzothiazol‐2‐ylsulfanyl}acetamide scaffold was identified during screening. Optimization of this initial hit by synthesis and screening of a focused compound library with this scaffold led to the identification of a novel uncompetitive inhibitor ( 1 a24 , IC₅₀=3.4±0.2 μM ) of the WNV NS2B‐NS3 protease. Molecular docking of 1 a24 into the WNV protease showed that the compound interferes with productive interactions of the NS2B cofactor with the NS3 protease and is an allosteric inhibitor of the WNV NS3 protease.     

The Synthesis and in vivo Evaluation of 2′,2′‐Difluoro KRN7000

The synthesis of 2′,2′‐difluoro KRN7000 is described. In vivo evaluation demonstrates that this fluorinated glycolipid induces CD1d‐dependent TCR activation of NKT cells, with a bias towards Th2 cytokine production.

     

Synthesis and characterization of new polyureas derived from 4‐(4′‐Methoxyphenyl)urazole

4‐(4′‐Methoxyphenyl)urazole (MPU) was prepared from 4‐methoxybenzoic acid in five steps. The reaction of monomer MPU with n‐isopropylisocyanate was performed at room temperature in N,N‐dimethylformamide solution, and the resulting bis‐urea derivative was obtained in high yield and was finally used as a model for polymerization reaction. The step‐growth polymerization reactions of monomer MPU with hexamethylene diioscyanate, isophorone diioscyanate, and toluene‐2,4‐diioscyanate were performed in N,N‐dimethylacetamide solution in the presence of pyridine as a catalyst. The resulting novel polyureas have an inherent viscosity (η_inh) in a range of 0.07–0.21 dL/g in DMF and sulfuric acid at 25°C. These polyureas were characterized by IR, ¹H‐NMR, elemental analysis, and TGA. Some physical properties and structural characterization of these novel polyureas are reported. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1141–1146, 2002     

Synthesis and Anti‐herpetic Activity of Phosphoramidate ProTides

Among the many prodrug approaches aimed at delivering nucleoside monophosphates into cells, the phosphoramidate ProTide approach is one that has shown success, which has made it possible for some of the phosphoramidates to enter into clinical trials. Herein, we report the synthesis and antiviral activity of a series of phosphoramidate ProTides designed to bypass the thymidine kinase (TK) dependence of the parent nucleoside analogues. Phosphoramidate derivatives of (E)‐5‐(2‐bromovinyl)‐2′‐deoxyuridine (BVDU) that contain L ‐alanine or pivaloyloxymethyl iminodiacetate (IDA‐POM) exhibit anti‐HSV‐1 and anti‐VZV activity in cell cultures, but they largely lost antiviral potency against TK‐deficient virus strains. Among deazapurine nucleosides and their phosphoramidate derivatives, the 7‐deazaadenine containing nucleosides and their phosphoramidate triester derivatives showed weak antiviral activity against VZV. Apparently, intracellular nucleotide delivery with these phosphoramidates is partly successful. However, none of the compound prodrugs showed superior activity to their parent drugs.