Synthesis and Cytostatic and Antiviral Activities of 2′‐Deoxy‐2′,2′‐difluororibo‐ and 2′‐Deoxy‐2′‐fluororibonucleosides Derived from 7‐(Het)aryl‐7‐deazaadenines

A series of sugar‐modified derivatives of cytostatic 7‐heteroaryl‐7‐deazaadenosines (2′‐deoxy‐2′‐fluororibo‐ and 2′‐deoxy‐2′,2′‐difluororibonucleosides) bearing an aryl or heteroaryl group at position 7 was prepared and screened for biological activity. The difluororibonucleosides were prepared by non‐ stereoselective glycosidation of 6‐chloro‐7‐deazapurine with benzoyl‐protected 2‐deoxy‐2,2‐difluoro‐D ‐erythro‐pentofuranosyl‐1‐mesylate, followed by amination and aqueous Suzuki cross‐couplings with (het)arylboronic acids. The fluororibo derivatives were prepared by aqueous palladium‐catalyzed cross‐coupling reactions of the corresponding 7‐iodo‐7‐deazaadenine 2′‐deoxy‐2′‐fluororibonucleoside 20 with (het)arylboronic acids. The key intermediate 20 was prepared by a six‐step sequence from the corresponding arabinonucleoside by selective protection of 3′‐ and 5′‐hydroxy groups with acid‐labile groups, followed by stereoselective S_N2 fluorination and deprotection. Some of the title nucleosides and 7‐iodo‐7‐deazaadenine intermediates showed micromolar cytostatic or anti‐HCV activity. The most active were 7‐iodo and 7‐ethynyl derivatives. The corresponding 2′‐deoxy‐2′,2′‐difluororibonucleoside 5′‐O‐triphosphates were found to be good substrates for bacterial DNA polymerases, but are inhibitors of human polymerase α.     

Synthesis and Biological Evaluation of Imidazo[2,1‐b][1,3,4]thiadiazole‐Linked Oxindoles as Potent Tubulin Polymerization Inhibitors

A series of imidazo[2,1‐b][1,3,4]thiadiazole‐linked oxindoles composed of an A, B, C and D ring system were synthesized and investigated for anti‐proliferative activity in various human cancer cell lines; test compounds were variously substituted at rings C and D. Among them, compounds 7 ((E)‐5‐fluoro‐3‐((6‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl)‐imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one), 11 ((E)‐3‐((6‐p‐tolyl‐2‐(3,4,5‐trimethoxyphenyl)imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one), and 15 ((E)‐6‐chloro‐3‐((6‐phenyl‐2‐(3,4,5‐trimethoxyphenyl)imidazo[2,1‐b][1,3,4]thiadiazol‐5‐yl)methylene)indolin‐2‐one) exhibited potent anti‐proliferative activity. Treatment with these three compounds resulted in accumulation of cells in G₂/M phase, inhibition of tubulin assembly, and increased cyclin‐B1 protein levels. Compound 7 displayed potent cytotoxicity, with an IC₅₀ range of 1.1–1.6 μM , and inhibited tubulin polymerization with an IC₅₀ value (0.15 μM ) lower than that of combretastatin A‐4 (1.16 μM ). Docking studies reveal that compounds 7 and 11 bind with αAsn101, βThr179, and βCys241 in the colchicine binding site of tubulin.     

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.     

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.     

Small‐Molecule APOBEC3G DNA Cytosine Deaminase Inhibitors Based on a 4‐Amino‐1,2,4‐triazole‐3‐thiol Scaffold

APOBEC3G (A3G) is a single‐stranded DNA cytosine deaminase that functions in innate immunity against retroviruses and retrotransposons. Although A3G can potently restrict Vif‐deficient HIV‐1 replication by catalyzing excessive levels of G→A hypermutation, sublethal levels of A3G‐catalyzed mutation may contribute to the high level of HIV‐1 fitness and its incurable prognosis. To chemically modulate A3G catalytic activity with the goal of decreasing the HIV‐1 genomic mutation rate, we synthesized and biochemically evaluated a class of 4‐amino‐1,2,4‐triazole‐3‐thiol small‐molecule inhibitors identified by high‐throughput screening. This class of compounds exhibits low‐micromolar (3.9–8.2 μM ) inhibitory potency and remarkable specificity for A3G versus the related cytosine deaminase, APOBEC3A. Chemical modification of inhibitors, A3G mutational screening, and thiol reactivity studies implicate C321, a residue proximal to the active site, as the critical A3G target for this class of molecules.     

Design,Synthesis, and Biological Evaluation of Unconventional Aminopyrimidine,Aminopurine, and Amino‐1,3,5‐triazine Methyloxynucleosides

Herein we describe a class of unconventional nucleosides (methyloxynucleosides) that combine unconventional nucleobases such as substituted aminopyrimidines, aminopurines, or aminotriazines with unusual sugars in their structures. The allitollyl or altritollyl derivatives were pursued as ribonucleoside mimics, whereas the tetrahydrofuran analogues were pursued as their dideoxynucleoside analogues. The compounds showed poor, if any, activity against a broad range of RNA and DNA viruses, including human immunodeficiency virus (HIV). This inactivity may be due to lack of an efficient metabolic conversion into their corresponding 5′‐triphosphates and poor affinity for their target enzymes (DNA/RNA polymerases). Several compounds showed cytostatic activity against proliferating human CD4⁺ T‐lymphocyte CEM cells and against several other tumor cell lines, including murine leukemia L1210 and human prostate PC3, kidney CAKI‐1, and cervical carcinoma HeLa cells. A few compounds were inhibitory to Moloney murine sarcoma virus (MSV) in C3H/3T3 cell cultures, with the 2,6‐diaminotri‐O‐benzyl‐D ‐allitolyl‐ and ‐D ‐altritolyl pyrimidine analogues being the most potent among them. This series of unconventional nucleosides may represent a novel family of potential antiproliferative agents.     

North‐ and South‐Bicyclo[3.1.0]Hexene Nucleosides: The Effect of Ring Planarity on Anti‐HIV Activity

The syntheses of new conformationally locked North‐ and South‐bicyclo[3.1.0]hexene nucleosides is reported. The North analogues were synthesized by a convergent approach from the known (1S,2R,5R)‐5‐[(tert‐butyldiphenylsilyloxy)methyl]bicyclo[3.1.0]hex‐3‐en‐2‐ol by Mitsunobu coupling with the nucleobases. The South analogues were synthesized from their bicyclo[3.1.0]hexane nucleoside precursors by the selective protection of the primary hydroxy group, conversion of the secondary alcohol into a good leaving group, and base‐catalyzed elimination to generate the olefin. The transformation of a bicyclo[3.1.0]hexane nucleoside into a bicyclo[3.1.0]hexene nucleoside flattens the five‐membered ring of the bicyclic system and rescues anti‐HIV activity for North‐D4T, North‐D4A, and South‐D4C. The relationship between planarity and the anti/syn disposition of the nucleobase that is favored by a particular pseudosugar platform are proposed as key parameters in controlling biological activity.     

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.     

Gold(I)‐Catalyzed Cascade for Synthesis of Pyrrolo[1,2‐a:2′,1′‐c]‐/Pyrido[2,1‐c]pyrrolo[1,2‐a]quinoxalinones

An efficient and convenient method was developed for the one‐pot construction of the complex polycyclic heterocycles pyrrolo[1,2‐a:2′,1′‐c]‐/pyrido[2,1‐c]pyrrolo[1,2‐a]quinoxalinones from two simple starting materials via a gold(I)‐catalyzed domino reaction. This strategy presents an atom economical and environmentally friendly transformation, in which two new C N bonds and one new C C bond are formed in a one‐pot reaction process.     

Synthesis and Biological Activity of 10‐Aza‐narciclasine

The first active aza analogue of narciclasine was synthesized from a pentasubstituted derivative of nicotinic acid. The key features of the synthesis include a halogen dance of bromopyridine and an intramolecular Heck reaction with a conduramine derived chemoenzymatically from bromobenzene. 10‐Aza‐narciclasine was found to have reasonable activity against several cancer cell lines.

     

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.     

Synthesis and Biological Evaluation of 9‐Oxo‐9H‐indeno[1,2‐b]pyrazine‐2,3‐dicarbonitrile Analogues as Potential Inhibitors of Deubiquitinating Enzymes

High‐throughput screening highlighted 9‐oxo‐9H‐indeno[1,2‐b]pyrazine‐2,3‐dicarbonitrile ( 1 ) as an active inhibitor of ubiquitin‐specific proteases (USPs), a family of hydrolytic enzymes involved in the removal of ubiquitin from protein substrates. The chemical behavior of compound 1 was examined. Moreover, the synthesis and in vitro evaluation of new compounds, analogues of 1 , led to the identification of potent and selective inhibitors of the deubiquitinating enzyme USP8.     

Dithieno[2,3‐d:2′,3′‐d′]naphtho[2,1‐b:3,4‐b′]dithiophene based medium bandgap conjugated polymers for photovoltaic applications

Three novel medium band gap (MBG) conjugated polymers (CPs) (named as P1, P2, and P3, respectively) were developed by copolymerizing 2,7‐dibromo‐10,11‐di(2‐hexyldecyloxy)dithieno[2,3‐d:2′,3′‐d′]naphtho[2,1‐b:3,4‐b′]dithiophene (NDT‐Br) with three different units: 2,5‐bis(tributylstannyl)thiophene, 2,5‐bis(trimethylstannyl)thieno[3,2‐b]thiophene and trans?1,2‐bis(tributylstannyl)ethene, respectively. The thermal, optical, and electrochemical properties of the polymers were investigated. All of the polymers have good thermal stability and medium band gap (～ 1.9 eV). Prototype bulk heterojunction photovoltaic cells based on the blend P1/P2/P3 and [6, 6] phenyl‐C61 butyric acid methyl ester (PC₆₁BM) were assembled and the photovoltaic properties were assessed. Power conversion efficiencies (PCEs) of 1.61% ～ 2.43% have been obtained under 100 mW cm^?2 illumination (AM1.5). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43288.     

Synthesis and in vitro Evaluation of 3H‐Pyrrolo[3,2‐f]quinolin‐9‐one Derivatives That Show Potent and Selective Anti‐leukemic Activity

A series of new substituted 7‐phenyl‐3H‐pyrrolo[3,2‐f]quinolin‐9‐ones were synthesized and evaluated for their antiproliferative activity. The most active derivatives showed high selectivity against human leukemia cell lines and potently inhibited their growth, with GI₅₀ values in the nanomolar range. The active compounds strongly blocked tubulin assembly and colchicine binding to tubulin. Their activities were equal to or greater than that of the reference compound combretastatin A‐4. Flow cytometry studies showed that the two most active compounds arrested Jurkat cells in the G₂/M cell‐cycle phase in a concentration‐dependent manner. This effect was associated with apoptosis, mitochondrial depolarization, generation of reactive oxygen species, activation of caspase‐3, and cleavage of the enzyme poly(ADP‐ribose) polymerase.     

Synthesis and Biological Evaluation of Indole‐2‐carbohydrazide Derivatives as Anticancer Agents with Anti‐angiogenic and Antiproliferative Activities

A novel series of indole‐2‐carbohydrazide derivatives were synthesized, characterized, and evaluated for their antiproliferative activities against two cancer cell lines, HCT116 and SW480, and a normal human fetal lung fibroblast cell line, MRC‐5. Among this series, compound 24 f displayed potent cytotoxic activities in vitro against HCT116 and SW480 cell lines with GI₅₀ values of 8.1 and 7.9 μm , respectively, and was inactive against MRC‐5 cells. The newly synthesized compounds were also evaluated for anti‐angiogenesis capabilities by chick chorioallantoic membrane, human umbilical vein endothelial cell (HUVEC) migration, and endothelial microtubule formation assays. Moreover, the effects of 24 f on the vascular endothelial growth factor receptor‐2 and the signaling pathway in HUVECs indicated that this compound inhibits VEGFR‐2 and its downstream related proteins. These results indicate that compound 24 f , as well as the other derivatives, are promising inhibitors of angiogenesis.