Appended Aromatic Moieties in Flexible Bis-3-chloropiperidines Confer Tropism against Pancreatic Cancer Cells

Nitrogen mustards (NMs) are an old but still largely diffused class of anticancer drugs. However, spreading mechanisms of resistance undermine their efficacy and therapeutic applicability. To expand their antitumour value, we developed bis-3-chloropiperidines (B-CePs), a new class of mustard-based alkylating agent, and we recently reported the striking selectivity for BxPC-3 pancreatic tumour cells of B-CePs bearing aromatic moieties embedded in the linker. In this study, we demonstrate that such tropism is shared by bis-3-chloropiperidines bearing appended aromatic groups in flexible linkers, whereas esters substituted by aliphatic groups or by efficient DNA-interacting groups are potent but nonselective cytotoxic agents. Besides, we describe how the critical balance between water stability and DNA reactivity can affect the properties of bis-3-chloropiperidines. Together, these findings support the exploitation of B-CePs as potential antitumour clinical candidates.     

Improvement of SNAr Reaction Rate by an Electron‐Withdrawing Group in the Crosslinking of DNA Cytosine‐5 Methyltransferase by a Covalent Oligodeoxyribonucleotide Inhibitor

DNA cytosine 5‐methyltransferase (DNMT) catalyzes methylation at the C5 position of the cytosine residues in the CpG sequence. Aberrant DNA methylation patterns are found in cancer cells. Therefore, inhibition of human DNMT is an effective strategy for treating various cancers. The inhibitors of DNMT have an electron‐deficient nucleobase because this group facilitates attack by the catalytic Cys residue in DNMTs. Recently, we reported the synthesis and properties of mechanism‐based modified nucleosides, 2‐amino‐4‐halopyridine‐C‐nucleosides (d^XP), as inhibitors of DNMT. To develop a more efficient inhibitor of DNMT for oligonucleotide therapeutics, oligodeoxyribonucleotides (ODNs) containing other nucleoside analogues, which react more quickly with DNMT, are needed. Herein, we describe the design, synthesis, and evaluation of the properties of 2‐amino‐3‐cyano‐4‐halopyridine‐C‐nucleosides (d^XP^CN) and ODNs containing d^XP^CN, as more reactive inhibitors of DNMTs. Nucleophilic aromatic substitution (S_NAr) of the designed nucleosides, d^XP^CN, was faster than that of d^XP, and the ODN containing d^XP^CN effectively formed a complex with DNMTs. This study suggests that the incorporation of an electron‐withdrawing group would be an effective method to increase reactivity toward the nucleophile of the DNMTs, while maintaining high specificity.     

Investigation of Vitamin D2 and Vitamin D3 Hydroxylation by Kutzneria albida

The active vitamin D metabolites 25-OH−D and 1α,25-(OH)₂−D play an essential role in controlling several cellular processes in the human body and are potentially effective in the treatment of several diseases, such as autoimmune diseases, cardiovascular diseases and cancer. The microbial synthesis of vitamin D₂ (VD₂) and vitamin D₃ (VD₃) metabolites has emerged as a suitable alternative to established complex chemical syntheses. In this study, a novel strain, Kutzneria albida, with the ability to form 25-OH−D₂ and 25-OH−D₃ was identified. To further improve the conversion of the poorly soluble substrates, several solubilizers were tested. 100-fold higher product concentrations of 25-OH−D₃ and tenfold higher concentrations of 25-OH−D₂ after addition of 5 % (w/v) 2-hydroxypropyl β-cyclodextrin (2-HPβCD) were reached. Besides the single-hydroxylation products, the human double-hydroxylation products 1,25-(OH)₂−D₂ and 1,25-(OH)₂−D₃ and various other potential single- and double-hydroxylation products were detected. Thus, K. albida represents a promising strain for the biotechnological production of VD₂ and VD₃ metabolites.     

Enhancement of VOCs removal using a novel double-tube packed bed catalytic dielectric barrier discharge (DPDBD) reactor

We developed a novel double-tube packed bed catalytic dielectric barrier discharge (DPDBD) reactor to degrade toluene. The DPDBD reactor contains four discharge cells with one power supply, namely, A–D. NiO/γ-Al₂O₃ is packed in cell A to effectively destroy the branched chains in toluene. TiO₂/γ-Al₂O₃ is packed in cell B owing to its high catalytic oxidation activity to weaken the benzene rings and mineralize the generated partial aromatic compounds. Cell C is a pure DBD process without any catalyst packed to thoroughly mineralize all the generated aromatic compounds and convert CO into CO₂ and NO into NO₂. γ-Al₂O₃ is packed in cell D to reduce the concentrations of byproducts, including O₃ and NO generated by air through oxidation. The combinations of the four discharge cells are optimized by the treatment of −3000 mg m⁻³ of toluene at 11 kV. In comparison with a double-tube dielectric barrier discharge (DDBD) reactor without catalyst packing and with a total discharge length of 6 cm, the selectivity of CO₂ was significantly improved from 45% to 57% when the discharge lengths of A, B, C, and D are 2, 4, 4, and 2 cm, respectively. Furthermore, the concentrations of O₃ and NO in the outlet can also be effectively reduced from 2.80 and 210 mg m⁻³ to 1.30 and 60 mg m⁻³, respectively. We also investigated the effects of applied voltage and styrene initial concentration.     

TET-Like Oxidation in 5-Methylcytosine and Derivatives: A Computational and Experimental Study

The epigenetic marker 5-methylcytosine (5mC) is an important factor in DNA modification and epigenetics. It can be modified through a three-step oxidation performed by ten-eleven-translocation (TET) enzymes and we have previously reported that the iron(IV)-oxo complex [Fe(O)(Py₅Me₂H)]²⁺ ( 1 ) can oxidize 5mC. Here, we report the reactivity of this iron(IV)-oxo complex towards a wider scope of methylated cytosine and uracil derivatives relevant for synthetic DNA applications, such as 1-methylcytosine (1mC), 5-methyl-iso-cytosine (5miC) and thymine (T/5mU). The observed kinetic parameters are corroborated by calculation of the C−H bond energies at the reactive sites which was found to be an efficient tool for reaction rate prediction of 1 towards methylated DNA bases. We identified oxidation products of methylated cytosine derivatives using HPLC-MS and GC-MS. Thereby, we shed light on the impact of the methyl group position and resulting C−H bond dissociation energies on reactivity towards TET-like oxidation.     

Studies on the Synthesis and Activity of Three Tripalladium Complexes Containing Planaramine Ligands

The present study deals with the synthesis, characterization and activity against human cancer cell lines: A2780, A2780^cisR and A2780^ZD0473R of three tripalladium complexes, MH3, MH4 and MH5, that each have two planaramine ligands bound to the central metal ion. Cellular uptake levels, extent of DNA binding, and nature of interaction with salmon sperm and pBR322 plasmid DNA were determined for each complex. Palladium compounds are much more reactive than their corresponding platinum derivatives, which makes them therapeutically inactive but toxic. However, the results of the present study suggest that significant antitumour activity can be introduced in palladium complexes by lessening their reactivity by the introduction of sterically hindered ligands such as 2‐hydroxypyridine, 3‐hydroxypyridine and 4‐hydroxypyridine. When bound to the central palladium ion, 4‐hydroxypyridine appears to be more activating than 2‐hydroxypyridine and 3‐hydroxypyridine, suggesting that noncovalent interactions, such as hydrogen bonding, may also be key determinants of antitumour activity in addition to the steric effect. While cisplatin binds with DNA to form intrastrand GG adducts that causes local bending of a DNA strand, these planaramine‐derived palladium complexes are expected to bind with DNA and form a number of long‐range interstrand GG adducts that would cause a global change in DNA conformation, provided the tripalladium cations in MH3, MH4 and MH5 persist under physiological conditions.     

Phenyl Selenide-Based Precursors as Hydrogen Peroxide Inducible DNA Interstrand Cross-Linkers

DNA interstrand crosslinks (ICLs) are highly toxic DNA lesions, and induce cell death by blocking DNA strand separation. Most ICL agents aiming to kill cancer cells, also generate adverse side effects to normal cells. H₂O₂-inducible DNA ICL agents are highly selective for targeting cancer cells, as the concentration of H₂O₂ is higher in cancer cells than normal cells. Previous studies have focused on arylboronate-based precursors, reacting with H₂O₂ to generate reactive quinone methides (QMs) crosslinking DNA. Here we explore phenyl selenide-based precursors 1 – 3 as H₂O₂-inducible DNA ICL agents. The precursors 1 – 3 can be activated by H₂O₂ to generate the good benzylic leaving group and promote production of reactive QMs to crosslink DNA. Moreover, the DNA cross-linking ability is enhanced by the introduction of substituents in the para-position of the phenolic hydroxyl group. From the substituents explored (H, OMe, F), the introduction of electron donating group (OMe) shows a pronounced elevating effect. Further mechanistic studies at the molecular and DNA levels confirm alkylation sites located mainly at dAs, dCs and dGs in DNA. Additionally, cellular experiments reveal that agents 1 – 3 exhibit higher cytotoxicity toward H1299 human lung cancer cells compared to clinically used drugs, by inducing cellular DNA damage, apoptosis and G0/G1 cell cycle arrest. This study provides a strategy to develop H₂O₂-inducible DNA interstrand cross-linkers.     

Unexpected Solvent Effects in the Isomerization of iPrPCPIr(η2-PhC≡CPh) to a 1-Iridaindene

The reaction of ^iPrPCPIr with diphenylacetylene (^iPrPCP=κ³-2,6-C₆H₃(CH₂P(ⁱPr)₂)₂), generated by dehydrogenation of ^iPrPCPIrH₄ with tert-butylethylene, readily provides the π-adduct ^iPrPCPIr(η²-PhC≡CPh) in quantitative yield at room temperature. Heating solutions of ^iPrPCPIr(η²-PhC≡CPh) in aromatic hydrocarbon solvents leads to isomerization forming the 1-iridaindene ^iPrPCPIr(C₈H₅(2-Ph)). Surprisingly, this seemingly intramolecular reaction presents a kinetic isotope effect of 4.6 in C₆H₆ versus C₆D₆ solvent. The rate of this isomerization is effected by the availability of easily activated C−H bonds (i. e. aromatic C(sp²)-H without ortho-substituents), and is strongly dependent upon the ratio of C−H to C−D bonds. Experiments indicate that many, or all, of the steps in this process may be reversible and that a highly fluxional C−H/D addition product is present during isomerization.     

Manganese‐Catalyzed ortho‐C−H Alkenylation of Aromatic N−H Imidates with Alkynes: Versatile Access to Mono‐Alkenylated Aromatic Nitriles

So far, the direct C−H alkenylation of aromatic nitriles with alkynes has not been achieved. Herein, we discribe the first manganese‐catalyzed C−H alkenylation of aromatic N−H imidates to access mono‐alkenylated aromatic nitriles. The reaction is accelerated by the presence of a catalytic amount of sodium pivalate. This protocol is also highlighted by the simple catalytic system, good compatibility of functional groups, and excellent mono‐/dialkenylation selectivity as well as E/Z stereoselectivity.

     

Metal-Organic Sheets for Efficient Drug Delivery and Bioimaging

Metal-organic frameworks (MOFs) formed by coordination between metal ions or clusters and organic bridging ligands possess great potential for biomedicine applications, given their high biocompatibility and biodegradability. Compared with the traditional three-dimensional (3D) MOFs, two-dimensional (2D) MOFs with sheet-like morphologies exhibit unique properties. In this study, a nanoscale 2D leaf-shaped MOF (NZIF−L) was synthesized via coordination self-assembly between 2-methylimidazole (Hmim) and Zn²⁺ with subsequent morphology and size control. The fabricated NZIF−L is cytocompatible and can be quickly endocytosed, which makes it an excellent cargo carrier. Subsequent to loading with either doxorubicin (DOX) or 4,4′-(1,2-diphenylvinyl)-1,2-di-(phenylcarboxylic acid) (TCPE), the respectively obtained DOX@NZIF−L and TCPE@NZIF−L showed promise for killing and imaging cancer cells.     

Assembly of Fully Substituted 2H-Indazoles Catalyzed by Cu2O Rhombic Dodecahedra and Evaluation of Anticancer Activity

Simultaneous C−N, and N−N bond-forming methods for one-pot transformations are highly challenging in synthetic organic chemistry. In this study, the Cu₂O rhombic dodecahedra-catalyzed synthesis of 2H-indazoles is demonstrated with good to excellent yields from readily available chemicals. This one-pot procedure involves Cu₂O nanoparticle-catalyzed consecutive C−N, and N−N bond formation followed by cyclization to yield 2H-indazoles with broad substrate scope and high functional group tolerance. Various cell-based bioassay studies demonstrated that 2H-indazoles inhibit the growth of cancer cells, typically through induction of apoptosis in a dose-dependent manner. Moreover, 2H-indazoles tested in the MDA-MB-468 cell line were capable of inhibiting cancer cell migration and invasion. Thus, it is shown that 2H-indazoles have potent in vitro anticancer activity that warrant further investigation of this compound class.     

Organocatalytic Enantioselective Aza‐Michael Addition of Purine Bases to α,β‐Unsaturated Ketones

The first organocatalytic enantioselective aza‐Michael addition of purine bases to α,β‐unsaturated ketones has been developed, affording Michael adducts in moderate to high yields (up to 96% yield) and high to excellent enantioselectivities (up to >99% ee). A wide range of α,β‐unsaturated ketones including aliphatic and aromatic enones are tolerated in this process, generally demonstrating good reactivity, regioselectivity and enantioselectivity. The aromatic α,β‐unsaturated ketones showing quite low reactivity in the reported catalytic systems, were first successfully employed as Michael acceptors in this transformation, yielding high enantioselectivities (up to 94% ee). The utility of this method was also applied for the synthesis of enantioenriched non‐natural nucleoside analogues with potential biological activities.     

Modelling and Phenotypic Screening of NAP-6 and 10-Cl-BBQ,AhR Ligands Displaying Selective Breast Cancer Cytotoxicity in Vitro

To exploit the interaction of the aryl hydrocarbon receptor (AhR) pathway in developing breast-cancer-specific cytotoxic compounds, we examined the breast cancer selectivity and the docking pose of the AhR ligands (Z)-2-(2-aminophenyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (NAP-6; 5 ) and 10-chloro-7H-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (10-Cl-BBQ; 6 ). While the breast cancer selectivity of 5 in vitro is known, we discuss the SAR around this lead and, by using phenotypic cell-line screening and the MTT assay, show for the first time that 6 also presents with breast cancer selectivity, notably in the triple-negative (TN) receptor breast cancer cell line MDA-MB-468, the ER+ breast cancer cell lines T47D, ZR-75-1 and the HER2+ breast cancer cell line SKBR3 (GI₅₀ values of 0.098, 0.97, 0.13 and 0.21 μM, respectively). Indeed, 6 is 55 times more potent in MDA-MB-468 cells than normal MCF10A breast cells (GI₅₀ of 0.098 vs 5.4 μM) and more than 130 times more potent than in cell lines derived from pancreas, brain and prostate (GI₅₀ of 0.098 vs 10–13 μM). Molecular docking poses of 5 and 6 together with analogue synthesis and phenotypic screening show the importance of the naphthalene moiety, and an ortho-disposed substituent on the N-phenyl moiety for biological activity.     

Predicting the reactivity of phenolic compounds with formaldehyde. II. Continuation of an ab initio study

Phenol–formaldehyde resins are important adhesives used by the forest products industry. The phenolic compounds in these resins are derived primarily from petrochemical sources. Alternate sources of phenolic compounds include tannins, lignins, biomass pyrolysis products, and coal gasification products. Because of variations in their chemical structures, the reactivities of these phenolic compounds with formaldehyde vary in quite subtle ways. Previously, it was demonstrated that the reactivity of a number of phenols with formaldehyde in nonaqueous conditions could be correlated with charges calculated for reactive sites on the aromatic ring (Conner, A. H. J Appl Polym Sci 2000, 78, 355–363). We studied the reactivity of a larger number of phenolic compounds with formaldehyde in an aqueous solution using sodium hydroxide as the catalyst. Reaction rates were determined from measurements of the concentrations of the phenolic compounds and formaldehyde as functions of time. The reaction rate constants varied over a wide range (approximately 10^?2 to 10⁴ L mol^?1 h^?1). An estimate of the reactivity per reactive site on the phenolic ring was determined by dividing the rate by the number of reactive sites. Atomic charges for each phenolic compound were calculated by ab initio methods at the RHF/6‐31+ G level of theory using the CHelpG method. The charge per reactive site was estimated by summing the charges at all the reactive sites on the phenolic ring and dividing by the number of reactive sites. A strong correlation was observed between the reactivity per reactive site and the average charge per reactive site. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 135–140, 2002     

Synthesis and Structure-Activity Relationships of 3-Arylisoquinolone Analogues as Highly Specific hCES2A Inhibitors

Mammalian carboxylesterases (CES) are key enzymes that participate in the hydrolytic metabolism of various endogenous and exogenous substrates. Human carboxylesterase 2A (hCES2A), mainly distributed in the small intestine and colon, plays a significant role in the hydrolysis of many drugs. In this study, 3-arylisoquinolones 3 h [3-(4-(benzyloxy)-3-methoxyphenyl)-7,8-dimethoxyisoquinolin-1(2H)-one] and 4 a [3-(4-(benzyloxy)-3-methoxyphenyl)-4-bromo-7,8-dimethoxyisoquinolin-1(2H)-one] were found to have potent inhibitory effects on hCES2A (IC₅₀=0.68 μΜ, K_i=0.36 μΜ) and excellent specificity (more than 147.05-fold over hCES1 A). Moreover, 4 a exhibited threefold improved inhibition on intracellular hCES2A in living HepG2 cells relative to 3 h , with an IC₅₀ value of 0.41 μΜ. Results of inhibition kinetics studies and molecular docking simulations demonstrate that both 3 h and 4 a can bind to multiple sites on hCES2A, functioning as mixed inhibitors. Structure−activity relationship analysis revealed that the lactam moiety on the B ring is crucial for specificity towards hCES2A, while a benzyloxy group is optimal for hCES2A inhibitory potency; the introduction of a bromine atom may enhance cell permeability, thereby increasing the intracellular hCES2A inhibitory activity.     

Synthesis and in Vitro Evaluation of Novel 5-Nitroindole Derivatives as c-Myc G-Quadruplex Binders with Anticancer Activity

Lead-optimization strategies for compounds targeting c-Myc G-quadruplex (G4) DNA are being pursued to develop anticancer drugs. Here, we investigate the structure-activity- relationship (SAR) of a newly synthesized series of molecules based on the pyrrolidine-substituted 5-nitro indole scaffold to target G4 DNA. Our synthesized series allows modulation of flexible elements with a structurally preserved scaffold. Biological and biophysical analyses illustrate that substituted 5-nitroindole scaffolds bind to the c-Myc promoter G-quadruplex. These compounds downregulate c-Myc expression and induce cell-cycle arrest in the sub-G1/G1 phase in cancer cells. They further increase the concentration of intracellular reactive oxygen species. NMR spectra show that three of the newly synthesized compounds interact with the terminal G-quartets (5′- and 3′-ends) in a 2 : 1 stoichiometry.     

Synthesis of Stereoisomeric N 6-Deoxyadenosine Adducts of syn- and anti- Dihydrodiol Epoxides of Benzo[a]pyrene and Their Incorporation into 18-mer DNA Sequences from Human Ha-ras Protooncogene

Oligonucleotide sequences synthesized with specifically positioned and structurally defined adducts of dihydrodiol epoxides (DE) of polycyclic aromatic hydrocarbons like benzo[a]pyrene (B[a]P) are useful tools to study in detail the solution structure of corresponding duplexes by NMR techniques as well as the interaction of a single adduct with DNA polymerases. Here we report the successful incorporation of trans-N ⁶-dA-B[a]PDE adducts derived from the syn- and anti-diastereomers of B[a]PDE into 18-mer oligonucleotides representing partial human Ha-ras sequences surrounding codon 61 (CAG). The key step in our approach is a nucleophilic displacement reaction of a deoxyinosine derivative activated at the 6-position by a sulfonate group with a racemic aminotriol providing a regio- and stereospecific synthesis of the N ⁶-dA adducts. The aminotriol precursors are prepared by direct aminolysis of the DE's or by a stereoselective opening of the oxirane ring with sodium azide followed by reduction. The fully protected diastereomeric trans-N ⁶-dA-B[a]PDE adducts were separated by preparative HPLC and subsequently transformed into the corresponding phosphoramidites. The synthesis of four 18-mers was performed on a DNA synthesizer incorporating in each sequence [d(5′-GGC·CA*G·GAG·GAG·TAC·AGC-3′)] a single dA adduct (A*) at Codon 61 using standard phosphoramidite chemistry. After extensive purification of the 18-mers by reverse phase HPLC and analysis by PAGE, the presence of the trans-N⁶ -dA-B[a]PDE adducts in the oligonucleotides was confirmed by fluorescence spectroscopy.     

Toxic Effects of the Major Components of Diesel Exhaust in Human Alveolar Basal Epithelial Cells (A549)

We investigated the toxicity of benzo[a]pyrene (B[a]P), 1-nitropyrene (1-NP) and 3-nitrobenzanthrone (3-NBA) in A549 cells. Cells were treated for 4 h and 24 h with: B[a]P (0.1 and 1 μM), 1-NP (1 and 10 μM) and 3-NBA (0.5 and 5 μM). Bulky DNA adducts, lipid peroxidation, DNA and protein oxidation and mRNA expression of CYP1A1, CYP1B1, NQO1, POR, AKR1C2 and COX2 were analyzed. Bulky DNA adducts were induced after both treatment periods; the effect of 1-NP was weak. 3-NBA induced high levels of bulky DNA adducts even after 4-h treatment, suggesting rapid metabolic activation. Oxidative DNA damage was not affected. 1-NP caused protein oxidation and weak induction of lipid peroxidation after 4-h incubation. 3-NBA induced lipid peroxidation after 24-h treatment. Unlike B[a]P, induction of the aryl hydrocarbon receptor, measured as mRNA expression levels of CYP1A1 and CYP1B1, was low after treatment with polycyclic aromatic hydrocarbon (PAH) nitro-derivatives. All test compounds induced mRNA expression of NQO1, POR, and AKR1C2 after 24-h treatment. AKR1C2 expression indicates involvement of processes associated with reactive oxygen species generation. This was supported further by COX2 expression induced by 24-h treatment with 1-NP. In summary, 3-NBA was the most potent genotoxicant, whereas 1-NP exhibited the strongest oxidative properties.     

Time-Integrated DNA Adduct Levels and Relative Tumorigenic Potencies of Six Polycyclic Aromatic Hydrocarbons in Strain A/J Mouse Lung

We have investigated the induction of DNA adducts and adenomas in the lungs of strain A/J mice following the i.p. administration of several polycyclic aromatic hydrocarbons (PAH): pyrene, dibenz[a,h]anthracene (DBA), benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), 5-methylchrysene (5-MeC), 3-methylcholanthrene (3-MC), and cyclopenta[cd]pyrene (CPP). All of the PAH induced lung adenomas, with relative tumor potency rankings as a function of administered dose: DBA = 3-MC > 5-MeC > CPP > B[a]P > B[b]F. DNA adducts reached maximal levels between 3 and 7 days after injection, followed by a gradual decrease. The time-integrated DNA adduct level (TIDAL) was calculated by numerically integrating the areas under the adduct persistence curves extrapolated out to 240 days for each PAH at each dose level. Tumorigenic potencies as a function of TIDAL values for 5-MeC, B[a]P, B[b]F, and CPP were all equal, while 3-MC was 2.6-fold more potent and DBA was 25.8-fold more potent.