Self-Assembly of Nanoparticles into Two-Dimensional Arrays for Catalytic Applications.

Self-assembly of nanoparticles (NPs) is at the heart of nanotechnology, and has shown many potential applications in fabricating nanodevices with highly controlled functionality. Two-dimensional (2D) arrays of NPs can provide a thin and uniform NP array with each NP being exposed on the surface to maximize NP catalysis. This minireview summarizes the recent progress on the fabrication and application of 2D NP arrays. It conveys the important message to readers that creation of libraries of NP arrays with varying catalytic strengths is an exciting direction in catalysis. This approach can be used to solve complicated catalytic problems in which multiple chemical reactions need to be catalyzed in a single reaction vessel.

Rational design of novel irreversible inhibitors for human arginase.

Parasites have developed a variety of strategies for invading hosts and escaping their immune response. A common mechanism by which parasites escape nitric oxide (NO) toxicity is the activation of host arginase. This activation leads to a depletion of l-arginine, which is the substrate for NO synthase, resulting in lower levels of NO and increased production of polyamines that are necessary for parasite growth and differentiation. For this reason, small molecule inhibitors for arginase show promise as new anti-parasitic chemotherapeutics. However, few arginase inhibitors have been reported. Here, we describe the discovery of novel irreversible arginase inhibitors, and their characterization using biochemical, kinetic, and structural studies. Importantly, we determined the site on human arginase that is labeled by one of the small molecule inhibitors. The tandem mass spectra data show that the inhibitor occupies the enzyme active site and forms a covalent bond with Thr135 of arginase. These findings pave the way for the development of more potent and selective irreversible arginase inhibitors.

Hydrodehalogenation of Polyhalogenated Aromatics Catalyzed by NiPd Nanoparticles Supported on Nitrogen-Doped Graphene.

Ni30 Pd70 nanoparticles supported on nitrogen-doped graphene (NG) acts as a catalyst for the hydrodehalogenation of halogenated aromatics under mild reaction conditions. It reduces mono- or dichloroarenes to the corresponding dehalogenated arenes in >90 % yield in 10 % aqueous isopropanol solvent at or below 50 °C within 5 h. Tests on a variety of substrates containing various functional groups show that the catalyst is selective for reduction of C-Cl and C-Br bonds. In addition, this catalyst completely hydrodehalogenates high-concentration solutions of dioxin, polychlorinated biphenyls, chloroaromatic constituents of the defoliant agent orange, and polybrominated diphenyl ethers in 12 h. The catalyst is reusable and shows no morphological or compositional changes after 5 cycles. This methodology offers a powerful, low-cost, and safe technology for the degradation of polyhalogenated aromatics, and may be useful for preventing proliferation of these toxins in the environment from causing serious health issues.

Maximizing the Catalytic Activity of Nanoparticles through Monolayer Assembly on Nitrogen-Doped Graphene.

We report a facile method for assembly of a monolayer array of nitrogen-doped graphene (NG) and nanoparticles (NPs) and the subsequent transfer of two layers onto a solid substrate (S). Using 3 nm NiPd NPs as an example, we demonstrate that NiPd-NG-Si (Si=silicon wafer) can function as a catalyst and show maximum NiPd catalysis for the hydrolysis of ammonia borane (H3 NBH3 , AB) with a turnover frequency (TOF) of 4896.8 h-1 and an activation energy (Ea ) of 18.8 kJ mol-1 . The NiPd-NG-S catalyst is also highly active for catalyzing the transfer hydrogenation from AB to nitro compounds, leading to the green synthesis of quinazolines in water. Our assembly method can be extended to other graphene and NP catalyst materials, providing a new 2D NP catalyst platform for catalyzing multiple reactions in one pot with maximum efficiency.

AgPd Nanoparticles Deposited on WO2.72 Nanorods as an Efficient Catalyst for One-Pot Conversion of Nitrophenol/Nitroacetophenone into Benzoxazole/Quinazoline.

We report a seed-mediated growth of 2.3 nm AgPd nanoparticles (NPs) in the presence of 40 × 5 nm WO2.72 nanorods (NRs) for the synthesis of AgPd/WO2.72 composites. The strong interactions between AgPd NPs and WO2.72 NRs make the composites, especially the Ag48Pd52/WO2.72, catalytically active for dehydrogenation of formic acid (TOF = 1718 h-1 and Ea = 31 kJ/mol) and one-pot reactions of formic acid, 2-nitrophenol, and aldehydes into benzoxazoles in near quantitative yields under mild conditions. The catalysis can also be extended to the one-pot reactions of ammonium formate, 2-nitroacetophenone, and aldehyde for high yield syntheses of quinazolines. Our studies demonstrate a new catalyst design to achieve a green chemistry approach to one-pot reactions for the syntheses of benzoxazoles and quinazolines.

Description of the cytotoxic effect of a novel drug Abietyl-Isothiocyanate on endometrial cancer cell lines.

The objective of the present study was to determine the in-vitro effect of Abietyl-Isothiocyanate (ABITC), a representative of a new class of anti-cancer drugs, on endometrial cancer (EC) cell lines. ABITC at concentrations ≥1 µM displayed dose-dependent and selective cytotoxicity to EC cell lines (ECC-1, AN3CA, RL95-2) in comparison to other cancer cell lines. After treatment with ABITC, ECC-1 unlike control cells displayed hallmark features of apoptosis including chromatin condensation and nuclear fragmentation. At concentrations below the IC50, ABITC exerted anti-proliferative effects by blocking cell-cycle progression through G0/G1 and S-phase. In addition, cells attempted to counteract drug treatment by pro-survival signaling such as deactivation of JNK/SAPK and p38 MAPK and activation of AKT and ErK1/2. ABITC also altered EGF-receptor phosphorylation. At a concentration of 5 µM ABITC generated an excess amount of reactive oxygen species (ROS) and displayed pro-apoptotic signaling such as activation of caspase-8, JNK-SAPK and deactivation of PARP-1. Co-treatment with an antioxidant blocked the drug effects by reducing ROS generation, cytotoxicity and pro-apoptotic signaling. In summary, novel isothiocyanate ABITC is an anti-proliferative and selectively cytotoxic drug to EC cells in-vitro. Key mechanisms during cell death are predominantly correlated to excess generation of ROS. We suggest the further development of ABITC as a potential therapeutic by studying the drug efficacy in EC in-vivo models.

Kinetic delay of cyclization/elimination-coupled enzyme assays: analysis and solution.

A kinetic analysis of an enzyme assay employing a synthetic substrate that produces a detectable signal through a spontaneous organic cyclization/elimination reaction following the enzymatic reaction was conducted. The results from the calculation were used to predict the lag period and provide accurate measurements of the activity of alkaline phosphatase using the fluorogenic substrate (1).

A focused library of protein tyrosine phosphatase inhibitors.

Protein tyrosine phosphatases such as PTP1B and YopH are potential targets for the development of therapeutic agents against a variety of pathological conditions including diabetes, obesity, and infection by the bacterium Yersinia pestis. A focused library of bidentate α-ketoacid-based inhibitors has been screened against several tyrosine phosphatases. Compound 2a has IC(50) values of 43 and 220 nM against YopH and PTP1B, respectively, and shows a 30-fold selectivity for PTP1B over the closely related phosphatase TCPTP.

The binding site of zinc and indium metal to amino acid derivatized squarate complexes - Implications in inhibitor and mediator designs.

Three novel metal squaric acid-peptide complexes, SQI-SQIII were prepared by addition of indium triflate or zinc chloride to the previously reported compounds [1], 3-(hydroxymethylamino)-4-(l-isoleucine methyl ester)-3-cyclobutene-1,2-dione (squarate 1), and 3-(hydroxymethylamino)-2-(l-isoleucine methyl ester)-4-thioxo-2-cyclobuten-1-one (squarate 2). The structures of SQI-SQIII were elucidated using NMR analysis. The electrochemical applications of two of these metal-squaric acid systems (SQI and SQII) were also investigated. Incorporation of SQII as a mediator, in the previously optimized Pt/p(HEMA)/p(pyrrole)/GOx electrode using the ionic liquid [bmim][BF(4)] as the solvent medium, produced a biosensor with enhanced properties, namely a sensitivity of 175.9mA/M d-glucose, working potential of +200mV, large linear range (0-12mM) and a detection limit of 1x10(-6)M.

Enantioselective synthesis of 1-aryltetrahydroisoquinolines.

1-Aryltetrahydroisoquinolines (1-arylTHIQs) are important structural motifs in many alkaloids and biologically active compounds. Ligand 2a promotes the enantioselective addition of arylzinc reagents to 3,4-dihydroisoquinoline N-oxide to yield (S)-1-arylTHIQs in 97-99% ee. Pinacol arylboronic esters are the optimal precursors for the arylzinc reagents. This method is applied to the enantioselective synthesis of Solifenacin.

Fluorogenic peptide substrates for serine and threonine phosphatases.

A new fluorescent assay for Ser/Thr protein phosphatases has been developed. Hydrolysis of a phosphoSer residue liberates the Ser hydroxyl group, which induces a cyclization reaction on the N-terminal carbamate and releases a fluorescent reporter. Sequence selectivity is observed using several peptide substrates against alkaline phosphatase (ALP), bacteriophage lambda protein phosphatase (lambda-PPase), and vaccinia H1 related phosphatase (VHR). These studies suggest that the assay could be a useful tool for profiling the substrate specificities of medicinally important phosphatases.

Macrocyclic inhibitors for the serine protease plasmin.

Macrocyclic inhibitors for the serine protease plasmin were synthesized and evaluated. The inhibitors were constructed starting from a cyclohexanone core. This core was linked to either the C- or N-terminus of a peptide so that the inhibitors were designed to interact with the non-primed or primed binding sites of the protease. Macrocycles were prepared by connecting the side chain of Tyr or Trp, via a short linker, to one end of the peptide. The activities of the macrocyclic inhibitors, while modest, were up to 10-fold more potent than a related non-cyclic analog.

Development of a specific inhibitor for the placental protease, cathepsin P.

Gene duplications in rodents have given rise to a family of proteases that are expressed exclusively in placenta. To define the biological role of these enzymes specific inhibitors are needed to differentiate their activities from other more ubiquitously expressed proteases, such as cathepsins B and L. Libraries of peptidyl inhibitors based upon a 4-cyclohexanone pharmacophore were screened for inhibition of cathepsins P, L, and B. The tightest binding dipeptidyl inhibitor for cathepsin P contained Tyr in P(2) and Trp in P(2)('), consistent with the specificity of this enzyme for hydrophobic amino acids at these sites in synthetic substrates. An inhibitor containing Trp in both P(2) and P(2)(') provided better discrimination between cathepsin P and cathepsins B and L. Extension of the inhibitors to include P(3), and P(3)(') amino acids identified an inhibitor with Trp in P(2), P(2)('), and P(3), and Phe in P(3)(') that bound to cathepsin P with a K(i) of 32 nM. This specificity for inhibitors with hydrophobic aromatic amino acids in these four positions is unique among the lysosomal cysteine proteases. This inhibitor bound to cathepsin P an order of magnitude tighter than to mouse and human cathepsin L and two orders of magnitude tighter than to human cathepsin B. Cbz-Trp-Trp-4-cyclohexanone-Trp-Phe-OMe can discriminate cathepsin P from cathepsins B and L and consequently can be used to specifically inhibit and identify cathepsin P in cellular systems.

A two stage click-based library of protein tyrosine phosphatase inhibitors.

Protein tyrosine phosphatases (PTPs) are important regulators of signal transduction pathways. Potent and selective PTP inhibitors are useful for probing these pathways and also may serve as drugs for the treatment of a variety of diseases including type 2 diabetes and infection by the bacterium Yersinia pestis. In this report Cu(I)-catalyzed 'click' cycloaddition reactions between azides and alkynes were employed to generate two sequential libraries of PTP inhibitors. In the first round library methyl 4-azidobenzoylformate was reacted with 56 mono- and diynes. After hydrolysis of the methyl esters, the resulting alpha-ketocarboxylic acids were assayed in crude form against the Yersinia PTP and PTP1B. Four compounds were selected for further evaluation, and one compound was chosen as the lead for generation of the second round library. This lead compound was modified by conversion of an alcohol into an azide group, and the resulting azide was reacted with the same 56 mono- and diynes that were used in the first generation library. After screening the crude inhibitors against the Yersinia PTP and PTP1B, four compounds were selected and evaluated in pure form against the Yersinia PTP, PTP1B, TCPTP, LAR, and CD45. The best bis(alpha-ketocarboxylic acid) inhibitor 34 had an IC(50) value of 550nM against the Yersinia PTP and an IC(50) value of 710nM against TCPTP. The most potent inhibitor containing a single alpha-ketocarboxylic acid group 32 had IC(50) values of 2.1, 5.7, and 2.6 microM against the Yersinia PTP, PTP1B, and TCPTP, respectively.

Structure-activity studies of cyclic ketone inhibitors of the serine protease plasmin: design, synthesis, and biological activity.

Three series of cyclic ketone inhibitors were synthesized and evaluated against the serine protease plasmin. Peptide inhibitors that incorporated 3-oxotetrahydrofuran and 3-oxotetrahydrothiophene 1,1-dioxide groups had the highest activities. Alkylamino substituents, which were designed to bind in the S1 subsite of plasmin, were attached to the inhibitors. Compounds 5c and 5g, which incorporated 6-aminohexyl substituents, were found to be optimal and demonstrated IC(50) values in the low micromolar range. Incorporating conformationally constrained peptide segments into the inhibitors did not improve their activities.

Enantioselective addition of vinylzinc reagents to 3,4-dihydroisoquinoline N-oxide.

Ligand 2a promotes the enantioselective addition of vinylzinc reagents to 3,4-dihydroisoquinoline N-oxide to yield chiral allylic hydroxylamines. With 0.1 equiv of the ligand, the product is obtained in up to 84% ee, whereas with 1.2 equiv of the ligand, the ee is increased to the 90-95% range with a variety of aliphatic, cyclic, and aromatic vinylzinc reagents. This method was used to synthesize the protected unnatural amino acid N-Cbz-d-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid in three steps from the allylic hydroxylamine.

Squaric acid-based peptidic inhibitors of matrix metalloprotease-1.

[structure: see text] A series of squaric acid-peptide conjugates were synthesized and evaluated as inhibitors of MMP-1. The cyclobut-3-enedione core was substituted at the 3-position with several functional groups, such as -N(alkyl)OH, -NHOH, and -OH, that are designed to bind to the zinc atom in the active site of the metalloprotease. The 4-position of the cyclobut-3-enedione was derivatized with mono- or dipeptides that are designed to bind in the S1' and S2' subsites of the enzyme, and position the metal chelating group appropriately in the active site for binding to zinc. Positional scanning revealed that -N(Me)OH provided the highest level of inhibition among the chelating groups that were tested, and Leu-Tle-NHMe was the preferred amino acid sequence. A combination of these groups yielded an inhibitor with an IC50 value of 95 microM. For one inhibitor, conversion of one of the carbonyl groups on the cyclobut-3-enedione core to a thiocarbonyl group resulted in a 18-fold increase in potency, and yielded a compound with an IC50 value of 15 microM.

Selective inhibitors of the serine protease plasmin: probing the S3 and S3' subsites using a combinatorial library.

A combinatorial library of 400 serine protease inhibitors with the general structure Cbz-X(aa)-Trp-cyclohexanone-Trp-Y(aa)-OH has been constructed. The library was synthesized on the solid phase using mix-and-split synthesis, where 20 different amino acids were incorporated at both the X(aa) and Y(aa) positions. These two positions correspond to the S3 and S3' subsites of the active site. Iterative deconvolution was used to identify hits from the library. The library was screened against four serine proteases: plasmin, kallikrein, thrombin, and trypsin. Seven inhibitors from the library that showed promising activities were resynthesized using solution-phase methods. Four of these compounds were good inhibitors of plasmin with IC(50) values in the range of 2.7-3.6 microM. The most potent of these inhibitors showed >150-fold selectivity for plasmin when compared to the other three serine proteases.

A comparison of cyclohexanone and tetrahydro-4H-thiopyran-4-one 1,1-dioxide as pharmacophores for the design of peptide-based inhibitors of the serine protease plasmin.

The plasminogen system is important in the proteolytic cascade that facilitates angiogenesis, a process that is essential for tumor growth and metastasis. The serine protease plasmin has a central role in the plasminogen system. This protease acts by degrading several components of the basement membrane and by activating other proteases. Therefore, inhibition of plasmin may be an effective method for blocking angiogenesis and, as a result, inhibiting the growth of primary tumors and secondary metastases. Three pairs of plasmin inhibitors were synthesized to compare the relative potency of inhibitors that are based upon a cyclohexanone or a tetrahydro-4H-thiopyran-4-one 1,1-dioxide nucleus. Compounds 1, 3, and 5 were cyclohexanone-based inhibitors, whereas compounds 2, 4, and 6 were tetrahydro-4H-thiopyran-4-one 1,1-dioxide-based inhibitors. Compounds 5 and 6 are reasonable inhibitors with IC50 values of 25 and 5.5 microM, respectively. Comparisons of the IC50 values of the three pairs show that the electron-withdrawing sulfone functional group is a beneficial element for the design of plasmin inhibitors. The presence of the sulfone increases inhibitor potency by a factor of 3-5 when compared to inhibitors that are based upon a simple cyclohexanone core.

Using enzyme inhibition as a high throughput method to measure the enantiomeric excess of a chiral sulfoxide.

[reaction: see text] The enantiomeric excess of methyl p-tolyl sulfoxide can be determined in a high throughput format by measuring its ability to inhibit the alcohol dehydrogenase catalyzed oxidation of ethanol. The two enantiomers of the sulfoxide have very different inhibition constants for the enzyme. Thus, the initial rate of ethanol oxidation in the presence of the sulfoxide is correlated with the sulfoxide enantiomeric excess.