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.     

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.     

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.     

A Thermostable Aldolase for the Synthesis of 3‐Deoxy‐2‐ulosonic Acids

A stereochemically promiscuous 2‐keto‐3‐deoxygluconate aldolase has been used as an efficient biocatalyst to catalyse the aldol reaction of pyruvate with C₃‐ and C₄‐aldoses to afford syn‐ and anti‐3‐deoxy‐2‐ulosonic acids in poor to good de. A continuous flow bioreactor containing immobilised aldolase has been developed that enables gram quantities of C₆‐ and C₇‐3‐deoxyhept‐2‐ulosonic acids to be produced in an efficient manner.     

Organosoluble polyimides derived from asymmetric 2‐substituted‐and 2,2′,6‐trisubstituted‐4,4′‐oxydianilines

We report a new method for the preparation of asymmetric diamines using 4,4′‐oxydianiline (4,4′‐ODA) as the starting material. By controlling the equivalents of bromination agent, N‐bromosuccinimide, we were able to attach bromide and phenyl substituents at the 2‐ or 2,2′,6‐positions of 4,4′‐ODA. Thus, four new asymmetric aromatic diamines, 2‐bromo‐4,4′‐oxydianiline (6), 2,2′,6‐tribromo‐4,4′‐oxydianiline (7), 2‐phenyl‐4,4′‐oxydianiline (8) and 2,2′,6‐triphenyl‐4,4′‐oxydianiline (9), were synthesized by this method. Their structural asymmetry was confirmed using ¹H NMR spectroscopy. Asymmetric polyimides (PI10–PI13) were prepared from these diamines and three different dianhydrides (pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride) in refluxing m‐cresol. The formed polyimides, except PI10a derived from 6 and PMDA, were all soluble in m‐cresol without premature precipitation during polymerization. These polyimides with inherent viscosity of 0.41–0.96 dL g^?1, measured at a concentration of 0.5 g dL^?1 in N‐methyl‐2‐pyrrolidone at 30 °C, can form tough and flexible films. Because of the structural asymmetry, they also exhibited enhanced solubility in organic solvents. Especially, polyimides PI11a and PI13a derived from 7 and 9 with rigid PMDA were soluble in various organic solvents at room temperature. The structural asymmetry of the prepared polyimides was also evidenced from ¹H NMR spectroscopy. In the ¹H NMR spectrum of PI11a, the protons of pyromellitic moiety appeared in an area ratio of 1:2:1 at three different chemical shifts, which were assigned to head‐to‐head, head‐to‐tail and tail‐to‐tail configurations, respectively. These polyimides also exhibited good thermal stability. Their glass transition temperatures ranged from 297 to 344 °C measured using thermal mechanical analysis. © 2013 Society of Chemical Industry     

Stabilization of Telomeric I‐Motif Structures by (2′S)‐2′‐Deoxy‐2′‐C‐Methylcytidine Residues

G‐quadruplexes and i‐motifs are tetraplex structures present in telomeres and the promoter regions of oncogenes. The possibility of producing nanodevices with pH‐sensitive functions has triggered interest in modified oligonucleotides with improved structural properties. We synthesized C‐rich oligonucleotides carrying conformationally restricted (2′S)‐2′‐deoxy‐2′‐C‐methyl‐cytidine units. The effect of this modified nucleoside on the stability of intramolecular i‐motifs from the vertebrate telomere was investigated by UV, CD, and NMR spectroscopy. The replacement of selected positions of the C‐core with C‐modified residues induced the formation of stable intercalated tetraplexes at near‐neutral pH. This study demonstrates the possibility of enhancing the stability of the i‐motif by chemical modification.     

Synthesis and Antiviral Evaluation of TriPPPro‐AbacavirTP,TriPPPro‐CarbovirTP,and Their 1′,2′‐cis‐Disubstituted Analogues

Herein we describe the synthesis of lipophilic triphosphate prodrugs of abacavir, carbovir, and their 1′,2′‐cis‐substituted carbocyclic analogues. The 1′,2′‐cis‐carbocyclic nucleosides were prepared by starting from enantiomerically pure (1R,2S)‐2‐((benzyloxy)methyl)cyclopent‐3‐en‐1‐ol by a microwave‐assisted Mitsunobu‐type reaction with 2‐amino‐6‐chloropurine. All four nucleoside analogues were prepared from their 2‐amino‐6‐chloropurine precursors. The nucleosides were converted into their corresponding nucleoside triphosphate prodrugs (TriPPPro approach) by application of the H‐phosphonate route. The TriPPPro compounds were hydrolyzed in different media, in which the formation of nucleoside triphosphates was proven. While the TriPPPro compounds of abacavir and carbovir showed increased antiviral activity over their parent nucleoside, the TriPPPro compounds of the 1′,2′‐cis‐substituted analogues as well as their parent nucleosides proved to be inactive against HIV.     

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 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.     

Synthesis and properties of organosoluble polyimides derived from 2,2′‐dibromo‐ and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianilines

Two new aromatic diamines, 2,2′‐dibromo‐4,4′‐oxydianiline (DB‐ODA 4 ) and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianiline (TB‐ODA 5 ), have been synthesized by oxidation, bromination, and reduction of 4,4′‐oxydianiline (4,4′‐ODA). Novel polyimides 6a–f and 7a–f were prepared by reacting DB‐ODA ( 4 ) and TB‐ODA ( 5 ) with several dianhydrides by one‐step method, respectively. The inherent viscosities of these polyimides ranged from 0.31 to 0.99 dL/g (0.5 g/dL, in NMP at 30°C). These polyimides showed enhanced solubilities compared to those derived from 4,4′‐oxydianiline and corresponding dianhydrides. Especially, polyimides 7a , derived from rigid PMDA and TB‐ODA ( 5 ) can also be soluble in THF, DMF, DMAc, DMSO, and NMP. These polyimides also exhibited good thermal stability. Their glass transition temperatures measured by thermal mechanical analysis (TMA) ranged from 251 to 328°C. When the same dianhydrides were used, polyimides 7 containing four bromide substituents had higher glass transition temperatures than polyimides 6 containing two bromide substituents. The effects of incorporating more polarizable bromides on the refractive indices of polyimides were also investigated. The average refractive indices (n_av) measured at 633 nm were from 1.6088 to 1.7072, and the in‐plane/out‐of‐plane birefringences (Δn) were from 0.0098 to 0.0445. It was found that the refractive indices are slightly higher when polyimides contain more bromides. However, this effect is not very obvious. It might be due to loose chain packing resulted from bromide substituents at the 2,2′ and 2,2′,6,6′ positions of the oxydiphenylene moieties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Recognition and Excision Properties of 8‐Halogenated‐7‐Deaza‐2′‐Deoxyguanosine as 8‐Oxo‐2′‐Deoxyguanosine Analogues and Fpg and hOGG1 Inhibitors

Cellular DNA continuously suffers various types of damage, and unrepaired damage increases disease progression risk. 8‐Oxo‐2′‐deoxyguanine (8‐oxo‐dG) is excised by repair enzymes, and their analogues are of interest as inhibitors and as bioprobes for study of these enzymes. We have developed 8‐halogenated‐7‐deaza‐2′‐deoxyguanosine derivatives that resemble 8‐oxo‐dG in that they adopt the syn conformation. In this study, we investigated their effects on Fpg (formamidopyrimidine DNA glycosylase) and hOGG1 (human 8‐oxoguanine DNA N‐glycosylase 1). Relative to 8‐oxo‐dG, Cl‐ and Br‐deaza‐dG were good substrates for Fpg, whereas they were less efficient substrates for hOGG1. Kinetics and binding experiments indicated that, although hOGG1 effectively binds Cl‐ and Br‐deaza‐dG analogues with low K_m values, their lower k_cat values result in low glycosylase activities. The benefits of the high binding affinities and low reactivities of 8‐oxo‐dG analogues with hOGG1 have been successfully applied to the competitive inhibition of the excision of 8‐oxoguanine from duplex DNA by hOGG1.     

Highly Regio‐ and Stereoselective Iodohydroxylation of Non‐ Heteroatom‐Substituted Allenes: An Efficient Synthesis of 4‐[3′‐Hydroxy‐2′‐iodoalk‐1′(Z)‐enyl]‐2(5H)‐furanone Derivatives

An efficient protocol for the highly regio‐ and stereoselective synthesis of 4‐(3′‐hydroxy‐2′‐iodoalk‐1′(Z)‐enyl)furan‐2(5H)‐one derivatives via selective iodohydroxylation of non‐heteroatom‐substituted allenes, i.e., 4‐allenyl‐2(5H)furanones, has been developed. The regio‐ and stereoselectivity of this reaction may be controlled by the electronic and steric effects of the furanone ring.     

Crosslinking of 1,9‐bis[glycidyloxypropyl]penta‐ (1′H,1′H,2′H,2′H‐perfluoroalkylmethylsiloxane)s with α,ω‐diaminoalkanes: The cure behavior and film properties

A series of nine films were prepared via phenol‐catalyzed thermal crosslinking reactions of 1,9‐bis‐ [glycidyloxypropyl]pentasiloxanes {1,9‐bis[glycidyloxypro‐ pyl]decamethylpentasiloxane (I), 1,9‐bis[glycidyloxypropyl]‐3,5,7‐tris(3′,3′,3′‐trifluoropropyl)heptamethylpentasiloxane (II), and 1,9‐bis[glycidyloxypropyl]‐3,5,7‐tris(1′H,1′H,2′H, 2′H‐perfluorooctyl)heptamethylpentasiloxane (III)} with α,ω‐diaminoalkanes [1,6‐diaminohexane (a), 1,8‐diaminooctane (b), and 1,12‐diaminododecane (c)]. The crosslink density was controlled by the choice of a–c. The cure behavior of I–III with a–c was studied with differential scanning calorimetry. The mechanical properties of the films were determined by dynamic mechanical thermal analysis. Their thermal stability was analyzed by thermogravimetric analysis. The surface properties of the films were evaluated with static contact‐angle measurements. These films represented a novel class of epoxies with an unusual combination of properties: high flexibility (low glass‐transition temperature), good thermal stability, and hydrophobic surfaces. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 203–210, 2004     

Synthesis and spectroelectrochemistry of dithieno(3,2‐b:2′,3′‐d)pyrrole derivatives

New π‐conjugated polymers containing dithieno(3,2‐b:2′,3′‐d)pyrrole (DTP) were successfully synthesized via electropolymerization. The effect of structural differences on the electrochemical and optoelectronic properties of the 4‐[4H‐dithieno(3,2‐b:2′,3′‐d)pyrrol‐4‐yl]aniline (DTP–aryl–NH₂), 10‐[4H‐dithiyeno(3,2‐b:2′,3′‐d)pirol‐4‐il]dekan‐1‐amine (DTP–alkyl–NH₂), and 1,10‐bis[4H‐dithieno(3,2‐b:2′,3′‐d)pyrrol‐4‐yl] decane (DTP–alkyl–DTP) were investigated. The corresponding polymers were characterized by cyclic voltammetry, NMR (¹H‐NMR and ¹³C‐NMR), and ultraviolet–visible spectroscopy. Changes in the electronic nature of the functional groups led to variations in the electrochemical properties of the π‐conjugated systems. The electroactive polymer films revealed redox couples and exhibited electrochromic behavior. The replacement of the DTP–alkyl–DTP unit with DTP–aryl–NH₂ and DTP–alkyl–NH₂ resulted in a lower oxidation potential. Both the poly(10‐(4H‐Dithiyeno[3,2‐b:2′,3′‐d]pirol‐4‐il)dekan‐1‐amin) (poly(DTP–alkyl–NH₂)) and poly(1,10‐bis(4H‐dithieno[3,2‐b:2′,3′‐d]pyrrol‐4‐yl) decane) (poly(DTP–alkyl–DTP)) films showed multicolor electrochromism and also fast switching times (<1 s) in the visible and near infrared regions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40701.     

Polymerase Synthesis and Restriction Enzyme Cleavage of DNA Containing 7‐Substituted 7‐Deazaguanine Nucleobases

Previous studies of polymerase synthesis of base‐modified DNAs and their cleavage by restriction enzymes have mostly related only to 5‐substituted pyrimidine and 7‐substituted 7‐deazaadenine nucleotides. Here we report the synthesis of a series of 7‐substituted 7‐deazaguanine 2′‐deoxyribonucleoside 5′‐O‐triphosphates (dG^RTPs), their use as substrates for polymerase synthesis of modified DNA and the influence of the modification on their cleavage by type II restriction endonucleases (REs). The dG^RTPs were generally good substrates for polymerases but the PCR products could not be visualised on agarose gels by intercalator staining, due to fluorescence quenching. The presence of 7‐substituted 7‐deazaguanine residues in recognition sequences of REs in most cases completely blocked the cleavage.     

Antioxidant mechanism of a 3‐arylbenzofuranone containing a 2′‐hydroxyl group

5‐Methyl‐7‐tert‐butyl‐3‐(2′hydroxyl‐5′‐methylphenyl)3H‐benzofuran‐2‐one (PCRBF2), is a better scavenger of 2,2‐diphenyl‐1‐picrylhydrazyl radicals than benzofuranone analogs without the 2′‐substituent, which indicates that PCRBF2 will cause good stabilization in polymers. To prove this further, antioxidation by PCRBF2 and other benzofuranone analogs, namely, 5‐methyl‐7‐tert‐butyl‐3‐(3′,4′‐dimethylphenyl)3H‐benzofuran‐2‐one (OXBF2) and 5‐methyl‐7‐tert‐butyl‐3‐(2′,5′‐dimethylphenyl)3H‐benzofuran‐2‐one (PXBF2), was comparatively studied in polypropylene. The resulting antioxidant activity order of these benzofuranones was PCRBF2 > OXBF2 > PXBF2, an observation showing that the hydroxyl group in the 2′‐position does not weaken the antioxidant activity of benzofuranone, but, on the contrary, increases it. Analyses by FTIR revealed intramolecular hydrogen bonding between the 3‐position hydrogen and the oxygen of the 2′‐hydroxyl group, which makes the 2′‐hydroxyl hydrogen of PCRBF2 more reactive than the 3‐position reactive hydrogen. Thus the hydroxyl group reacts with radicals first. J. VINYL ADDIT. TECHNOL., 19:198‐202, 2013. © 2013 Society of Plastics Engineers     

Palladium‐Catalyzed Three‐Component Tandem Cyclization Reaction of 2‐(2,3‐Allenyl)acylacetates,Organic Halides,and Amines: An Effective Protocol for the Synthesis of 4,5‐Dihydro‐1H‐pyrrole Derivatives

A domino three‐component reaction of 2‐(2′,3′‐allenyl)acylacetates with aryl or alkenyl halides and aryl‐ or benzylamines afforded 4,5‐dihydro‐1H‐pyrrole derivatives highly chemo‐ and regioselectively in one pot through imine formation/imine‐enamine tautomerization under the catalysis of palladium(0) and toluenesulfonic acid monohydrate. A high diastereoselectivity was observed.     

6‐Substituted 2‐Aminopurine‐2′‐deoxyribonucleoside 5′‐Triphosphates that Trace Cytosine Methylation

Gene expression is extensively regulated by the occurrence and distribution of the epigenetic marker 2′‐deoxy 5‐methylcytosine (5mC) in genomic DNA. Because of its effects on tumorigenesis there is an important link to human health. In addition, detection of 5mC can serve as an outstanding biomarker for diagnostics as well as for disease therapy. Our previous studies have already shown that, by processing O⁶‐alkylated 2′‐deoxyguanosine triphosphate (dGTP) analogues, DNA polymerases are able to sense the presence of a single 5mC unit in a template. Here we present the synthesis and evaluation of an extended toolbox of 6‐substituted 2‐aminopurine‐2′‐deoxyribonucleoside 5′‐triphosphates modified at position 6 with various functionalities. We found that sensing of 5‐methylation by this class of nucleotides is more general, not being restricted to O⁶‐alkyl modification of dGTP but also applying to other functionalities.     

Nonenzymatic Oligomerization of 3′,5′‐Cyclic CMP Induced by Proton and UV Irradiation Hints at a Nonfastidious Origin of RNA

We report that 3′,5′‐cyclic CMP undergoes nonenzymatic di‐ and trimerization at 20 °C under dry conditions upon proton or UV irradiation. The reaction involves stacking of the cyclic monomers and subsequent polymerization through serial transphosphorylations between the stacked monomers. Proton‐ and UV‐induced oligomerization of 3′,5′‐cyclic CMP demonstrates that pyrimidines—similar to purines—might also have taken part in the spontaneous generation of RNA under plausible prebiotic conditions as well as in an extraterrestrial context. The observed polymerization of naturally occurring 3′,5′‐cyclic nucleotides supports the possibility that the extant genetic nucleic acids might have originated by way of a straight Occamian path, starting from simple reactions between plausibly preactivated monomers.