Substituent Effects and Mechanism in a Mechanochemical Reaction.

We report the effect of substituents on the force-induced reactivity of a spiropyran mechanophore. Using single molecule force spectroscopy, force-rate behavior was determined for a series of spiropyran derivatives substituted with H, Br, or NO2 para to the breaking spirocyclic C-O bond. The force required to achieve the rate constants of ∼10 s-1 necessary to observe transitions in the force spectroscopy experiments depends on the substituent, with the more electron withdrawing substituent requiring less force. Rate constants at 375 pN were determined for all three derivatives, and the force-coupled rate dependence on substituent identity is well explained by a Hammett linear free energy relationship with a value of ρ = 2.9, consistent with a highly polar transition state with heterolytic, dissociative character. The methodology paves the way for further application of linear free energy relationships and physical organic methodologies to mechanochemical reactions, and the characterization of new force probes should enable additional, quantitative studies of force-coupled molecular behavior in polymeric materials.

Through-space (19)F-(19)F spin-spin coupling in ortho-fluoro Z-azobenzene.

We report through-space (TS) (19)F-(19)F coupling for ortho-fluoro-substituted Z-azobenzenes. The magnitude of the TS-coupling constant ((TS) JFF ) ranged from 2.2-5.9 Hz. Using empirical formulas reported in the literature, these coupling constants correspond to non-bonded F-F distances (dFF) of 3.0-3.5 Å. These non-bonded distances are significantly smaller than those determined by X-ray crystallography or density functional theory, which argues that simple models of (19)F-(19)F TS spin-spin coupling solely based dFF are not applicable. (1)H, (13)C and (19)F data are reported for both the E and Z isomers of ten fluorinated azobenzenes. Density functional theory [B3YLP/6-311++G(d,p)] was used to calculate (19) F chemical shifts, and the calculated values deviated 0.3-10.0 ppm compared with experimental values.

C-H functionalization directed by transformable nitrogen heterocycles: synthesis of ortho-oxygenated arylnaphthalenes from arylphthalazines.

Two protocols for oxygenation of aromatic C-H bonds ortho-positioned to the phthalazine ring were developed. The transannulation of the phthalazine ring to a naphthalene moiety by an Inverse Electron Demand Diels-Alder (IEDDA) reaction led to the synthesis of naphtho[2,1-c]chromenes, 1-(ortho-hydroxyaryl)naphthalenes and 6,7-dihydrobenzo[b]naphtho[1,2-d]oxepine. This new strategy based on the utilization of transformable nitrogen heterocycles in C-H functionalization chemistry can be potentially applicable to the synthesis of a broad range of biaryl compounds.

Green Approach toward Triazole forming Reactions for Developing Anticancer Drugs.

Compounds containing triazole have many significant applications in the dye and ink industry, corrosion inhibitors, polymers, and pharmaceutical industries. These compounds possess many antimicrobial, antioxidant, anticancer, antiviral, anti-HIV, antitubercular, and anticancer activities. Several synthetic methods have been reported for reducing time, minimizing synthetic steps, and utilizing less hazardous and toxic solvents and reagents to improve the yield of triazoles and their analogues synthesis. Among the improvement in methods, green approaches towards triazole forming biologically active compounds, especially anticancer compounds, would be very important for pharmaceutical industries as well as global research community. In this article, we have reviewed the last five years of green chemistry approaches on click reaction between alkyl azide and alkynes to install 1,2,3-triazole moiety in natural products and synthetic drug-like molecules, such as in colchicine, flavanone cardanol, bisphosphonates, thiabendazoles, piperazine, prostanoid, flavonoid, quinoxalines, C-azanucleoside, dibenzylamine, and aryl-azotriazole. The cytotoxicity of triazole hybrid analogues was evaluated against a panel of cancer cell lines, including multidrug-resistant cell lines.

Ag colloids and Ag clusters over EDAPTMS-coated silica nanoparticles: synthesis, characterization, and antibacterial activity against Escherichia coli.

To produce better antibacterial water-insoluble nanocomposites of silver (Ag), silver-silicon dioxide (Ag-SiO(2)) hybrid and silver colloid (Ag-c) nanoparticles (NPs) were studied. Ag-c NPs were synthesized using reduction of AgNO(3), and Ag-SiO(2) composites were prepared on a core of silica NPs functionalized with ethylenediamino-propyltrimethoxysilane, where Ag clusters were fabricated on amino groups using seed-mediated growth and characterized by transmission electron microscopy and ultraviolet-visible absorption spectroscopy. Antibacterial effectiveness of the Ag-SiO(2) NPs was tested against general Escherichia coli (E. coli ATCC 25922) and E. coli O157:H7 by measuring the growth based on optical density and digital counting of live-dead cells using a fluorescent microscope, and a field emission scanning electron microscope. Minimum inhibitory concentration values were studied against four representative bacteria along with E. coli O157:H7. Results showed that Ag NPs of 6.6 ± 4.5 nm were attached to the surface of SiO(2) NPs (74 ± 13.5 nm), and the Ag-c NPs (3.5 ± 2 nm) showed excellent antibacterial properties. FROM THE CLINICAL EDITOR: In this paper, the synthesis of Ag colloids and Ag clusters over EDAPTMS-coated silica nanoparticles is reported. Both NPs were examined for antibacterial effectiveness against representative bacteria including E. coli O157:H7 and found to have excellent antibacterial properties.

Ultra-sensitive detection of bacterial toxin with silicon nanowire transistor.

Nanowire field effect transistors (nano-FET) were lithographically fabricated using 50 nm doped polysilicon nanowires attached to two small gold terminals separated from each other by a approximately 150 nm gap to serve as the basis for electronic detection of bacteria toxins. The device characterizations, semiconducting properties and use in a robust and sensitive bio-molecular detection sensor of bacterial toxins were reported in this work. The device characteristics were demonstrated with varying gate and drain voltages. The bio-molecular detection was demonstrated using electrochemical impedance spectroscopy (EIS), using Staphylococcus aureus Enterotoxin B (SEB) as the target molecule. The detection limit of SEB was observed in the range of 10-35 fM.

Nanowire-transistor based ultra-sensitive DNA methylation detection.

Accurate detection of DNA methylation at specific gene transcription sites is important to identify potential tumor formation since this epigenetic alteration may result in silencing of tumor suppressor genes that protect against tumor formation or that repair damaged DNA. Current technologies used in DNA methylation detection are complicated and time consuming. This work presents the first nanowire field effect transistor (FET) based biosensor technology which achieves simple and ultra-sensitive electronic DNA methylation detection and avoids complicated bisulfite treatment and PCR amplification. The promoter of the p16(INK) gene, a tumor suppressor gene, is the target DNA in the detection model. The target DNA was captured and concentrated with magnetic beads, and released to the sensing surface of a nano-FET through a reversible binding process. The methylated p16(INK) promoter was recognized and bound to monoclonal anti-5-methylcytosine antibodies which were immobilized on the nano-FET sensing surface. The presence of the target DNA molecules induced electronic charge and changed the electronic properties of the nano-transistor from which detectable electronic signals are generated. The electronic charge based DNA methylation detection is simple and ultra-sensitive with the potential for low cost. The detection sensitivity was achieved at 2.5 x 10(-19) mol with no false positives observed.

Non-enzymatic aqueous peroxyoxalate chemiluminescence immune detection using a CCD camera and a CMOS device.

A new method for non-enzymatic aqueous peroxyoxalate chemiluminescence (POCL) biomolecular detection using imaging chip-based devices has been developed. A water-soluble amide of oxalic acid was synthesized and used in the investigation and characterization of POCL immunodetection in an aqueous environment. Six fluorescent dyes commonly used in biological detection were tested, and the intensity of light generated from the aqueous POCL reactions was characterized in the liquid phase. Direct detection sensitivity comparisons between a standard fluorescent method and this POCL method were performed in both liquid and solid phases. Results showed that detection sensitivity using the POCL method is comparable to that of the fluorescent method. POCL biomolecular detection on a nitrocellulose membrane was also investigated using a charge-coupled device (CCD) camera. Again, POCL detection sensitivity proved to be comparable to that using the fluorescent detection method. In an application of aqueous POCL biomolecular detection, Staphylococcus aureus enterotoxin B (SEB) and its antibody were used to demonstrate immuno- and affinity detection. For further applications, such as DNA and protein arrays, simultaneous detection of biomolecules labelled with different fluorescent labels was investigated, using a complementary metal oxide semiconductor (CMOS) colour imaging chip.

A novel homogeneous bioluminescence resonance energy transfer element for biomolecular detection with CCD camera or CMOS device.

A novel optical signal element based on homogeneous bioluminescence resonance energy transfer (BRET) was developed for biomolecular detection. A fluorescent dye and alkaline phosphatase (AP) conjugate was used as a reporter and light-generation element for imaging detection platforms that use a CCD camera or CMOS chip-based devices. In the presence of a luminescence substrate, the energy from the first light emission of a bioluminescence enzymatic reaction was transferred to fluorescent dyes which were conjugated to an enzyme. This resulted in a second light emission with a shorter wavelength. The second light was localized at the position of target molecules without the diffusion problems present in current technology. To optimize energy transfer efficiency, the ratio of enzyme to fluorophore in the conjugates, the fluorescent dyes used in the conjugates and the luminescence substrates used for BRET were investigated. BRET was demonstrated by using both a CCD camera and a CMOS imaging device. Image spatial resolution was greatly improved compared with conventional chemiluminescence detection. This new signal element opens a door for the direct measurement of fluorescent signals on an imaging chip without an external light source and portable instrumentation normally required for the fluorescent detection of biomolecules.

Enhanced Release of Molecules upon Ultraviolet (UV) Light Irradiation from Photoresponsive Hydrogels Prepared from Bifunctional Azobenzene and Four-Arm Poly(ethylene glycol).

Advances in biosensors and drug delivery are dependent on hydrogels that respond to external stimuli. In this work, we describe the preparation and characterization of photoresponsive hydrogels prepared by cross-linking of di-NHS ester of azobenzoic acid and four-armed, amine-terminated poly(ethylene glycol). The porous structure and composition of the hydrogels were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The reversible photoisomerization of the azobenzene-containing hydrogel cross-linkers in the gels was confirmed by absorption spectroscopy. Specifically, the photoisomerization of the cross-linkers between their trans and cis configurations was observed by monitoring the absorbance of the hydrogels at the two characteristic peaks of azobenzene (π-π* at 330 nm and n-π* at 435 nm). The effect of photoisomerization on the hydrogel structure was investigated by microscopy. Ultraviolet (UV) irradiation-induced reduction in hydrogel size was observed, which may be a result of the inherently smaller footprint of the cis azobenzene conformation, as well as dipole-dipole interactions between the polar cis azobenzene and the polymer network. The UV-triggered reduction in hydrogel size was accompanied by enhanced release of the near-infrared fluorescent dye Alexa Fluor 750 (AF750). Enhanced release of AF750 was observed in samples irradiated with UV versus dark control. Together, these data demonstrate the potential of these systems as reversible photoresponsive biomaterials.

Photoresponsive azo-combretastatin A-4 analogues.

Colchicine analogues in which an azo group is incorporated into a molecule containing the key pharmacophore of colchicine, have found particular utility as switchable tubulin binding chemotherapeutics. Combretastatin is a related compound containing a stilbene fragment that shows different bioactivity for the cis and trans isomers. We have performed cell assays on 17 new compounds structurally related to a previously reported azo-analogue of combretastatin. One of these compounds showed enhanced potency against HeLa (IC50 = 0.11 µM) and H157 cells (IC50 = 0.20 µM) for cell studies under 400 nm irradiation and the highest photoactivity (IC50 with irradiation/IC50 in dark = 550). We have performed docking and physicochemical studies of this new compound (7). Kinetic studies in water reveal a longer half-life for the cis isomer of 7 which may be one factor responsible for the better IC50 values in cell assays and the improved photoresponsive behavior.

Biodegradable DNA-enabled poly(ethylene glycol) hydrogels prepared by copper-free click chemistry.

Significant research has focused on investigating the potential of hydrogels in various applications and, in particular, in medicine. Specifically, hydrogels that are biodegradable lend promise to many therapeutic and biosensing applications. Endonucleases are critical for mechanisms of DNA repair. However, they are also known to be overexpressed in cancer and to be present in wounds with bacterial contamination. In this work, we set out to demonstrate the preparation of DNA-enabled hydrogels that could be degraded by nucleases. Specifically, hydrogels were prepared through the reaction of dibenzocyclooctyne-functionalized multi-arm poly(ethylene glycol) with azide-functionalized single-stranded DNA in aqueous solutions via copper-free click chemistry. Through the use of this method, biodegradable hydrogels were formed at room temperature in buffered saline solutions that mimic physiological conditions, avoiding possible harmful effects associated with other polymerization techniques that can be detrimental to cells or other bioactive molecules. The degradation of these DNA-cross-linked hydrogels upon exposure to the model endonucleases Benzonase(®) and DNase I was studied. In addition, the ability of the hydrogels to act as depots for encapsulation and nuclease-controlled release of a model protein was demonstrated. This model has the potential to be tailored and expanded upon for use in a variety of applications where mild hydrogel preparation techniques and controlled material degradation are necessary including in drug delivery and wound healing systems.

A novel multiple tyrosine-kinase targeted agent to explore the future perspectives of anti-angiogenic therapy for the treatment of multiple solid tumors: cabozantinib.

The process of angiogenesis involves the formation of new blood vessels from pre-existing vasculature by the over expression of certain factors leading to the growth and development of all solid tumor types. Hepatocyte growth factor receptor abbreviated as c-Met and vascular endothelial growth factor abbreviated as VEGF are some of the factors responsible for the induction in tumor growth and development. Recently a number of analogues associated with these receptors are under study. US FDA on November 29, 2012 approved a drug named cabozantinib formerly known as XL184 which is being marketed under the trade name of Cometriq for the treatment of Medullary Thyroid Cancer (MTC). Designing of the drug has been done in such a fashion that it can inhibit both VEGFR2 and c-Met simultaneously without over expressing any of the factors leading to the inhibition of angiogenesis. The drug is still under study for the evaluation of its efficacy in cases of many other solid tumor types including breast cancer, castration resistant prostate cancer (CRPC), renal cell carcinoma (RCC), hepatocellular carcinoma (HCC), gastric or gastroesophageal junction cancer, melanoma, small cell lung cancer (SCLC), ovarian cancer and primary peritoneal or fallopian tube carcinoma. This review article consists of preclinical and clinical data of cabozantinib and its efficacy and safety towards various types of solid tumors.

Photocontrolled micellar aggregation of amphiphilic DNA-azobenzene conjugates.

We demonstrate the reversible micellar aggregation of a DNA-azobenzene conjugate in aqueous conditions, in which the photoisomerization of the initially apolar trans-azobenzene moiety to the polar cis isomer causes disassembly of the aggregates. The molecular basis for this phenomena is a change in the hydrophobic/hydrophilic balance of the conjugate as the more polar cis azobenzene isomer is formed upon exposure to 365 nm irradiation. The conjugates were prepared by copper-free Click chemistry between an azide-modified, 53-base ssDNA and a cyclooctyne derivative of azobenzene. The photocontrolled aggregation of the conjugate was studied by dynamic light scattering and atomic force microscopy. The reversible micellar aggregation for a DNA-azobenzene conjugate has not been previously reported and holds promise for photocontrolled drug delivery applications.

Therapeutic agents triggering nonapoptotic cancer cell death.

It is widely recognized that the evasion of apoptotic cell death is one of the hallmarks of cancer. For many years cytotoxic agents have been developed to target apoptotic cell death as a main method of treating cancer. However, the occurrence of cellular defects involving the apoptotic machinery in many cancers has resulted in an acquired resistance to apoptotic cell death, undermining the effectiveness of chemotherapeutic agents. Over the past decade, research has revealed a growing number of cell death pathways that are not dependent on apoptosis. In addition, compounds specifically triggering these alternative cell death pathways have been identified and explored as novel cancer treatment options. These novel anticancer agents are critically discussed by the authors, and therefore, the current Perspective represents a resource for a practicing medicinal chemist looking for new opportunities to combat cancers resistant to the established proapoptotic therapeutic agents.

Exploring natural product chemistry and biology with multicomponent reactions. 5. Discovery of a novel tubulin-targeting scaffold derived from the rigidin family of marine alkaloids.

We developed synthetic chemistry to access the marine alkaloid rigidins and over 40 synthetic analogues based on the 7-deazaxanthine, 7-deazaadenine, 7-deazapurine, and 7-deazahypoxanthine skeletons. Analogues based on the 7-deazahypoxanthine skeleton exhibited nanomolar potencies against cell lines representing cancers with dismal prognoses, tumor metastases, and multidrug resistant cells. Studies aimed at elucidating the mode(s) of action of the 7-deazahypoxanthines in cancer cells revealed that they inhibited in vitro tubulin polymerization and disorganized microtubules in live HeLa cells. Experiments evaluating the effects of the 7-deazahypoxanthines on the binding of [(3)H]colchicine to tubulin identified the colchicine site on tubulin as the most likely target for these compounds in cancer cells. Because many microtubule-targeting compounds are successfully used to fight cancer in the clinic, we believe the new chemical class of antitubulin agents represented by the 7-deazahypoxanthine rigidin analogues have significant potential as new anticancer agents.

DNA detection on lateral flow test strips: enhanced signal sensitivity using LNA-conjugated gold nanoparticles.

A lateral flow test strip assay, enabling sensitive detection of DNA specific to the foodborne pathogen E. coli O157:H7, is described. The use of LNA-conjugated gold nanoparticle probes, along with signal amplification protocols, results in minimum detectable concentrations of ~0.4 nM.

Fluorescence sensing of zinc(II) using ordered mesoporous silica material (MCM-41) functionalized with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide.

A novel fluorescent zinc sensor was designed and synthesized on ordered mesoporous silica material, MCM-41, with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide (QTEPA; 3) using a simple one-step molecular self-assembly of the silane. The solution and solid samples were characterized using solid-state nuclear magnetic resonance, transmission electron microscopy, diffuse-reflectance infrared Fourier transform, and thermogravimetric analysis techniques. The QTEPA-modified MCM-41 (4) shows 3-fold fluorescence emission enhancement and about a 55 nm red shift upon addition of 1 µM Zn(II) ions in a Tris-HCl (pH 7.22) aqueous buffer solution. The UV-vis absorption maximum is at 330 ± 5 nm, and the fluorescence emission maximum wavelength is at 468 nm, with an increase in quantum yield from 0.032 to 0.106 under the same conditions. The presence of other metal ions has no observable effect on the sensitivity and selectivity of 4. This system selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 µM. The MCM-41-based systems have the advantage that they can be employed in aqueous solutions without any aggregation.

8-aminoquinoline functionalized silica nanoparticles: a fluorescent nanosensor for detection of divalent zinc in aqueous and in yeast cell suspension.

Zinc is one of the most important transition metal of physiological importance, existing primarily as a divalent cation. A number of sensors have been developed for Zn(II) detection. Here, we present a novel fluorescent nanosensor for Zn(II) detection using a derivative of 8-aminoquinoline (N-(quinolin-8-yl)-2-(3 (triethoxysilyl)propylamino)acetamide (QTEPA) grafted on silica nanoparticles (SiNPs). These functionalized SiNPs were used to demonstrate specific detection of Zn(II) in tris-HCl buffer (pH 7.22), in yeast cell (Saccharomyces cerevisiae) suspension, and in tap water. The silane QTEPA, SiNPs and final product were characterized using solution and solid state nuclear magnetic resonance, Fourier transform infrared, ultraviolet-visible absorption spectroscopy, transmission electron microscopy, elemental analysis, thermogravimetric techniques, and fluorescence spectroscopy. The nanosensor shows almost 2.8-fold fluorescence emission enhancement and about 55 nm red-shift upon excitation with 330 ± 5 nm wavelength in presence of 1 µM Zn(II) ions in tris-HCl (pH 7.22). The presence of other metal ions has no observable effect on the sensitivity and selectivity of nanosensor. This sensor selectively detects Zn(II) ions with submicromolar detection to a limit of 0.1 µM. The sensor shows good applicability in the determination of Zn(II) in tris-HCl buffer and yeast cell environment. Further, it shows enhancement in fluorescence intensity in tap water samples.

Three-component synthesis and anticancer evaluation of polycyclic indenopyridines lead to the discovery of a novel indenoheterocycle with potent apoptosis inducing properties.

A multicomponent reaction of indane-1,3-dione, an aldehyde and an amine-containing aromatic compound leading to the formation of indenopyridine-based heterocyclic medicinal scaffolds has been investigated. It was found that the yields significantly improve when oxygen gas is bubbled through the reaction mixture, facilitating the oxidation of the intermediate dihydropyridine-containing compounds to their aromatic counterparts. Investigation of the reaction scope revealed that formaldehyde, as well as various aliphatic, aromatic and heteroaromatic aldehydes, works well as the aldehyde component. In addition, substituted anilines and diverse aminoheterocycles can be utilized in this process as the amine-containing component. Preliminary biological evaluation of the synthesized library identified a pyrimidine-based polycycle, which rivals the anticancer drug etoposide in its toxicity and apoptosis inducing properties toward a human T-cell leukemia cell line.