Search

The protein kinase Aurora A, and its close relative, Aurora B, regulate human cell division. Aurora A is frequently overexpressed in cancers of the breast, ovary, pancreas and blood, provoking genome instability and resistance to anti-mitotic chemotherapy. Intracellular localization and enzymatic activity of Aurora A are regulated by its interaction with the spindle assembly factor TPX2. Here, we have used fragment-based, structure-guided lead discovery to develop small-molecule inhibitors of the Aurora A-TPX2 protein-protein interaction (PPI). These compounds act by novel mechanism compared to existing Aurora A inhibitors and they are highly specific to Aurora A over Aurora B. We identify a biophysically, structurally and phenotypically validated lead compound,CAM2602, exhibits oral bioavailability, favourable pharmacokinetics, pharmacodynamic biomarker modulation, and arrest of growth in tumour xenografts. Consistent with our original finding that Aurora A overexpression drives taxane-resistance in cancer cells,CAM2602synergizes with paclitaxel to suppress the outgrowth of pancreatic cancer cells. Our results provide a structural and chemical blueprint for targeting the Aurora A-TPX2 PPI for cancer therapy and suggest a promising clinical utility for this mode of action.

We report the facile amide-forming ligation of acylsilanes with hydroxylamines (ASHA ligation) under aqueous conditions. The ligation is fast, chemoselective, mild, high-yielding and displays excellent functional-group tolerance. Late-stage modifications of an array of marketed drugs, peptides, natural products, and biologically active compounds showcase the robustness and functional-group tolerance of the reaction. The key to the success of the reaction could be the possible formation of the strong Si-O bond via a Brook-type rearrangement. Given its simplicity and efficiency, this ligation has the potential to unfold new applications in the areas of medicinal chemistry and chemical biology.

Herein, we disclose the first set of unique selenium-containing SLAP (SiLicon Amine Protocol) reagents for the direct synthesis of C3/C5-substituted selenomorpholines and 1,4-selenazepanes from diverse (hetero)aldehydes under mild photocatalytic conditions. Enantiomerically pure 1,2-amino alcohol/α-amino acid versions of these heterocycles were also synthesized. Further, we have shown the late-stage modification of certain biologically active agents using the developed seleno-SLAP reagents.

We describe the synthesis of a range of 6’-triazolyl-dihydroxanthene-hemicyanine (DHX-hemicyanine) fused dyes through an effective copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction, with the dual aim of providing molecular diversity and fine tuning spectral properties of these near-infrared (NIR)-active materials. This was implemented by reacting 16 different aliphatic and aromatic azides with a terminal alkynyl-based-DHX-hemicyanine hybrid scaffold prepared in four steps and 35% overall yield from 4-bromosalicylaldehyde. The resulting triazole derivatives have been fully characterized and their optical properties determined both in organic solvents and simulated physiological conditions (phosphate buffered saline containing 5% of bovine serum albumin protein). This systematic study is a first important step towards the development of NIR-I fluorogenic "click-on" dyes or related photoactive agents for light-based diagnostic and/or therapeutic applications.

Herein, we disclose the first set of unique selenium-containing SnAP reagents for the direct synthesis of C-substituted selenomorpholines and 1,4-selenazepanes, including their amino acid derivatives from commercially available aldehydes under mild conditions. These elusive N-unprotected heterocycles are not accessible by classical routes. Biological evaluation of these compounds revealed promising activities against clinically relevant fungal strains.

[Image: see text] The development of an efficient synthetic route toward rim-differentiated C(5)-symmetric pillar[5]arenes (P[5]s), whose two rims are decorated with different chemical functionalities, opens up successive transformations of this macrocyclic scaffold. This paper describes a gram-scale synthesis of a C(5)-symmetric penta-hydroxy P[5] precursor, and a range of highly efficient reactions that allow functionalizing either rim at will via, e.g., sulfur(VI) fluoride exchange (SuFEx) reactions, esterifications, or Suzuki–Miyaura coupling. Afterward, BBr(3) demethylation activates another rim for similar functionalizations.

Potassium acyltrifluoroborates (KATs) are opening up new avenues in chemical biology, materials science and synthetic organic chemistry due to their intriguing reactivities. However, the synthesis of these compounds remains mostly complicated and time-consuming. This lack of a rapid and facile synthetic route has hindered the widespread adoption of KAT-based chemistry, especially in the areas of compound library synthesis and drug discovery. Herein, we have developed chemoselective Pd-catalyzed approaches for the late-stage diversification of arenes bearing pre-functionalized KATs. These approaches feature chemoselective cross-coupling, rapid diversification, functional group tolerance, mild reaction conditions, and high yields.

Summary BRCA2 controls RAD51 recombinase during homologous DNA recombination (HDR) through eight evolutionarily conserved BRC repeats, which individually engage RAD51 via the motif Phe-x-x-Ala. Using structure-guided molecular design, templated on a monomeric thermostable chimera between human RAD51 and archaeal RadA, we identify CAM833, a 529 Da orthosteric inhibitor of RAD51:BRC with a Kd of 366 nM. The quinoline of CAM833 occupies a hotspot, the Phe-binding pocket on RAD51 and the methyl of the substituted α-methylbenzyl group occupies the Ala-binding pocket. In cells, CAM833 diminishes formation of damage-induced RAD51 nuclear foci; inhibits RAD51 molecular clustering, suppressing extended RAD51 filament assembly; potentiates cytotoxicity by ionizing radiation, augmenting 4N cell-cycle arrest and apoptotic cell death and works with poly-ADP ribose polymerase (PARP)1 inhibitors to suppress growth in BRCA2-wildtype cells. Thus, chemical inhibition of the protein-protein interaction between BRCA2 and RAD51 disrupts HDR and potentiates DNA damage-induced cell death, with implications for cancer therapy., Graphical abstract, Highlights • CAM833 inhibits the protein-protein interaction between RAD51 and BRCA2 • Crystal structure shows CAM833 binds RAD51 at the same site as the BRCA2 FxxA motif • CAM833 blocks formation of RAD51 foci and filaments, preventing DNA repair • CAM833 potentiates cytotoxicity by IR and synergises with PARP1 inhibitors, Scott et al. describe CAM833, an inhibitor of DNA recombinase RAD51, that binds at the site normally occupied by the BRC repeats of the BRCA2 protein. Through blocking this protein-protein interaction, CAM833 is able to prevent RAD51-mediated homologous recombination and thus potentiate cancer cells to damage by radiation or PARP1 inhibition.

SUMMARYBRCA2 controls RAD51 recombinase during homologous DNA recombination (HDR) through eight evolutionarily-conserved BRC repeats, which individually engage RAD51 via the motif Phe-x-x-Ala. Using structure-guided molecular design, templated on a monomeric thermostable chimera between human RAD51 and archaeal RadA, we identify CAM833, a 529 Da orthosteric inhibitor of RAD51:BRC with a Kd of 366 nM. The quinoline of CAM833 occupies a hotspot, the Phe-binding pocket on RAD51 and the methyl of the substituted α-methylbenzyl group occupies the Ala-binding pocket. In cells, CAM833 diminishes formation of damage-induced RAD51 nuclear foci; inhibits RAD51 molecular clustering, suppressing extended RAD51 filament assembly; potentiates cytotoxicity by ionising radiation, augmenting 4N cell-cycle arrest and apoptotic cell death and works with poly-ADP ribose polymerase (PARP)1 inhibitors to suppress growth in BRCA2-wildtype cells. Thus, chemical inhibition of the protein-protein interaction between BRCA2 and RAD51 disrupts HDR and potentiates DNA damage-induced cell death, with implications for cancer therapy.

International audience; We describe an expedient access to a 5', 6', 7'-trifluoro dihydroxanthene-hemicyanine fused scaffold in 2 steps and 54% overall yield from the corresponding salicylic aldehyde. A 6'-regioselective nucleophilic aromatic substitution (SNAr) reaction with a wide range of nitrogen, sulfur or selenium nucleophiles then gives access to 16 near-infrared (NIR) fluorophores emitting in the 710-750 nm range. We also report the experimental and theoretical photophysical investigations of these unique optical agents that include the first series of 6'-heavy atom substituted dihydroxanthenes, extending the pool of polyfluorinated markers for biomedical and material applications.

A mild one-pot protocol for the synthesis of symmetrical biaryls by sequential Ir-catalyzed C-H borylation and Cu-catalyzed homocoupling of arenes is described. The regiochemistry of the biaryl formed is sterically controlled as dictated by the C-H borylation step. The methodology is also successfully extended to heteroarenes. Some of the products obtained by this approach are impossible to obtain via the Ullmann or the Suzuki coupling protocols. Finally, we have shown a one-pot sequence describing C-H borylation/Cu-catalyzed homocoupling/Pd-catalyzed Suzuki coupling to obtain π-extended arene frameworks.

Herein, we report the meta-nitration of arenes bearing ortho/para directing group(s) using the iridium-catalyzed C-H borylation reaction followed by a newly developed copper(II)-catalyzed transformation of the crude aryl pinacol boronate esters into the corresponding nitroarenes in a one-pot fashion. This protocol allows the synthesis of meta-nitrated arenes that are tedious to prepare or require multistep synthesis using the existing methods. The reaction tolerates a wide array of ortho/para-directing groups, such as -F, -Cl, -Br, -CH3 , -Et, -iPr -OCH3 , and -OCF3 . It also provides regioselective access to the nitro derivatives of π-electron-deficient heterocycles, such as pyridine and quinoline derivatives. The application of this method is demonstrated in the late-stage modification of complex molecules and also in the gram-scale preparation of an intermediate en route to the FDA-approved drug Nilotinib. Finally, we have shown that the nitro product obtained by this strategy can also be directly converted to the aniline or hindered amine through Baran's amination protocol.

Deregulation of protein kinase activity has been linked to many diseases ranging from cancer to AIDS and neurodegenerative diseases. Not surprisingly, drugging the human kinome - the complete set of kinases encoded by the human genome - has been one of the major drug discovery pipelines. Majority of the approved clinical kinase inhibitors target the ATP binding site of kinases. However, the remarkable sequence and structural similarity of ATP binding pockets of kinases make selective inhibition of kinases a daunting task. To circumvent these issues, allosteric inhibitors that target sites other than the orthosteric ATP binding pocket have been developed. The structural diversity of the allosteric sites allows these inhibitors to have higher selectivity, lower toxicity and improved physiochemical properties and overcome drug resistance associated with the use of conventional kinase inhibitors. In this chapter, we will focus on the allosteric inhibitors of selected serine/threonine kinases, outline the benefits of using these inhibitors and discuss the challenges and future opportunities.

A 26-member library of novel N-hydroxyquinolinone derivatives was synthesized by a one-pot Buchwald-type palladium catalyzed amidation and condensation sequence. The design of these rare scaffolds was inspired from N-hydroxypyridones and 2-quinolinones classes of compounds which have been shown to have rich biological activities. The synthesized compounds were evaluated for their anti-plasmodial and anti-bacterial properties. In addition, these compounds were screened for their iron(II)-chelation properties. Notably, four of these compounds exhibited anti-plasmodial activities comparable to that of the natural product cordypyridone B.

Background: Aurora A (AurA) kinase is a key mitotic protein implicated in cancer. Several small molecule inhibitors targeting the ATP binding site of this enzyme are in various stages of clinical development. However, these inhibitors can result in selectivity and drug resistance problems. Allosteric inhibition of kinases using small molecules is an alternative strategy to target these enzymes selectively and these could serve as the seeds for next generation medicines. This review discusses the developments in the non-ATP site binding small molecule inhibitors of AurA and their prospect as future therapeutics. Discussion: Allosteric targeting of AurA kinase using small molecules is relatively a new strategy, and only a handful of research work has been reported. Two patents and three papers pertaining to allosteric targeting of AurA kinase using small molecules were covered in this review. Topics discussed include, identification of small molecule inhibitors targeting AurA- Targeting Protein for Xenopus kinesin-like protein 2 (TPX2) interaction, anacardic acid - a natural product ligand that selectively modulates AurA activity in the presence of Aurora B kinase, and identification of felodipine as an uncompetitive inhibitor of AurA using Surface Enhanced Raman Spectroscopy (SERS) technique Conclusion: Allosteric targeting of therapeutically relevant enzymes using small molecules is a burgeoning research area. New techniques such as fragment-based ligand discovery, SERS methods, etc., are expanding to identify the allosteric site binding ligands. Research in this area is expected to deliver fruitful outcome in terms of novel therapeutics against AurA kinase as well as other therapeutically relevant enzymes.

International audience; A late-stage amination of a bifunctional dihydroxanthene (DHX) scaffold is reported to access a wide variety of new near-infrared (NIR) chromophores/fluorophores. The divergent approach allows the coupling of aliphatic and aromatic amines and readily provides molecular diversity shedding light on the structure fluorescence relationship of this emerging class of NIR fluorophores.

A approximately 3500-member library of bidentate inhibitors against protein tyrosine phosphatases (PTPs) was rapidly assembled using click chemistry. Subsequent high-throughput screening had led to the discovery of highly potent (K(i) as low as 150 nM) and selective MptpB inhibitors, some of which represent the most potent MptpB inhibitors developed to date.

An efficient strategy for the solid-phase synthesis of azidomethylene inhibitors targeting cysteine proteases is described. The method is highlighted by its compatibility with readily available building blocks, as well as its ability to accommodate different functional groups. A 249-member library has thus far been successfully synthesized, characterized, and screened against Caspase-1, -3 and -7.

Click chemistry is emerging as a powerful tool to elucidate the complex catalytic functions that enzymes perform in the biological system. Recent advances in proteomics heavily rely on the robust, modular and high-throughput platform offered by click chemistry. This minireview focuses on the central role click chemistry has played on the most recent advances in the chemical proteomic research involving the discovery of enzyme inhibitors and enzyme profiling using Activity-Based Probes (ABPs). The strength and benefit of click chemistry and its novel variants, such as the so-called in situ screening using click chemistry have been even more evident recently when this novel chemistry is coupled with high-throughput assay technologies such as microarrays and characterization techniques such as Liquid Chromatography-Mass Spectrometry in Selected Ion Mode (LCMS-SIM) and multidimensional LC-MS. The invaluable contribution of click chemistry in the emerging field of “Catalomics” is thus firmly established.

The first regioselective one-pot protocol for the conversion of arylic C—H bonds into 1,2,3-triazoles is presented.

In the post-genomic era, the characterization of enzyme activity patterns is more meaningful than enzyme identification. This is because the so-called substrate fingerprint of an enzyme reveals the type of chemical entities accepted by the enzyme as its potential substrates, and thereby helps in a better understanding of its catalytic mechanism and properties. Similarly, the unique pattern generated for an unknown enzyme by using a set of known substrates can be used to delineate its identity. With the aid of standard analytical tools, traditional fingerprinting experiments use a whole spectrum of substrates and/or their analogues on a target enzyme to create quantitative and reproducible profiles directly related to the enzyme’s activity. Different classes of enzymes have been studied in this fashion, including cytochrome P450, protein kinases, and hydrolytic enzymes. In recent years, much effort has been expended in developing microarray-based bioassays. If adopted for fingerprinting experiments, they could potentially provide a powerful platform by allowing the simultaneous analysis of thousands of enzymatic reactions on a single chip with very small sample volumes, while retaining a good degree of detection sensitivity. Proteases, one of the largest groups of enzymes that are important therapeutic targets of major human diseases, have been the focus of new enzyme-assay developments in recent years. Activity-based profiling (ABP), originally developed by Cravatt et al. , allows the proteases present in a crude proteome to be studied on the basis of their enzymatic activities rather than their relative abundance. ABP works by using either mechanismor affinity-based chemical probes that can be covalently attached to different classes of enzymes, thus providing a versatile tool for large-scale protease identification, characterization, and even fingerprinting experiments. We recently investigated a new class of ABP probes that target all major classes of proteases by their properties as enzyme substrates, rather than as inhibitors. For this reason, we expect that these probes will be more suitable for protease fingerprinting experiments than existing ones. We now report the chemical synthesis of a full set of these probes and their use in activity-based fingerprinting of proteases in gel-based experiments, as well as their potential application in microarraybased enzyme assays. A total of 16 probes were synthesized (Scheme 1), each containing a common p-aminomandelic acid moiety and a unique recognition head consisting of an N-acetylated amino acid that mimics the P1 position in a protease substrate. The amide bond between the two groups imitates the scissile bond in the protease substrate. A fluorescent reporter group, Cy3, was attached to the other end of p-aminomandelic acid. Upon proteolytic cleavage of the scissile bond, the probe releases the amino acid head group to generate a highly reactive quinolimine methide, which subsequently reacts covalently with the protease (that cleaves it) and renders it detectable (Scheme 1, left). One potential limitation of our enzyme-fingerprinting approach is that, since only P-site residues can be incorporated into the probe design, the approach might only be suitable for profiling proteases that possess P-site specificities. To make the 16 probes, commercially available p-nitrophenylacetic acid (17) was treated with thionyl chloride in methanol to afford the methyl ester 18 in 93% yield. Subsequently, the benzylic proton in 18 was brominated by N-Bromosuccinimide (NBS; 85% yield) to generate 19. This was followed by conversion to the corresponding benzyl alcohol 21 in two steps. Reduction of the nitro group in 21 with 10% Pd/C in the presence of H2 gave intermediate 22 in excellent yield (93%). A number of acylating reagents were tested in order to optimize the subsequent coupling reaction between the aromatic amine on 22 and a properly protected amino acid (both N-a-Boc and N-aFmoc amino acids were used), and it was found that O-(7azabenzotriazole-1-yl)-N,N,N’,N’-tetramethyluronium hexafluorophosphate (HATU) consistently gave the best yield (80–88% on average). By using the optimized method, 16 different amino acids were used to generate 16 versions of compound 23 in which each compound differed by its amino acid side chain. After deprotection of the N-a-Fmoc or N-a-Boc group, the resulting amino acids were acylated with acetic anhydride in N,N-diisopropylethylamine (DIEA) to afford 24. The hydrolytic cleavage of the methyl ester in 24 was achieved by using LiOH solution in nearly quantitative yield to furnish 25. The final 16 probes, represented by the single-letter codes of their amino acid (Table 1), were subsequently obtained in three steps by conversion of the benzylic OH group in 25 to the corresponding fluoride with (diethylamino)sulfur trifluoride (DAST) at 0 8C, and attachment of a reporter Cy3 dye via a hydrophilic linker. The average yield of these three steps combined for all sixteen probes was approximately 50%. The labeling experiments were first performed with four of the 16 probes synthesized F, K, Y, and W, and four commercially available proteases, trypsin, actinase E, b-chymotrypsin, and a-chymotrypsin. Both geland microarray-based labeling experiments were carried out (Figure 1). Control experiments were run with nonprotease proteins including bovine serum albumin (BSA), alkaline phosphatase, lysozyme, and lipase; but no labeling was observed even after prolonged incubation of these proteins with the probes (see Supporting Information and ref. [6]). As shown in Figure 1 (top), all four proteases were positively labeled by the different substrate-based probes, with [a] R. Srinivasan, X. Huang, S. L. Ng, Prof. Dr. S. Q. Yao Department of Chemistry, National University of Singapore 3 Science Drive 3, Singapore 117543 (Republic of Singapore) Fax: (+65)677-91691 E-mail : chmyaosq@nus.edu.sg [b] Prof. Dr. S. Q. Yao Department of Biological Sciences, National University of Singapore 14 Science Drive 4, Singapore 117543 (Republic of Singapore) Supporting information for this article is available on the WWW under http://www.chembiochem.org or from the author.

The post-genomic era heralds a multitude of challenges for chemists and biologists alike, with the study of protein functions at the heart of much research. The elucidation of protein structure, localization, stability, post-translational modifications, and protein interactions will steadily unveil the role of each protein and its associated biological function in the cell. The push to develop new technologies has necessitated the integration of various disciplines in science. Consequently, the role of chemistry has never been so profound in the study of biological processes. By combining the strengths of recombinant DNA technology, protein splicing, organic chemistry, and the chemoselective chemistry of native chemical ligation, various strategies have been successfully developed and applied to chemoselectively label proteins, both in vitro and in live cells, with biotin, fluorescent, and other small molecule probes. The site-specific incorporation of molecular entities with unique chemical functionalities in proteins has many potential applications in chemical and biological studies of proteins. In this article, we highlight recent progress of these strategies in several areas related to proteomics and chemical biology, namely, in vitro and in vivo protein biotinylation, protein microarray technologies for large-scale protein analysis, and live-cell bioimaging.

We review various advancements in small molecule probes, intein-based labeling methods, and the incorporation of synthetic amino acids into proteins for live cell imaging experiments. Finally, recent developments in quantum dots-based labeling are briefly reviewed.

A one-pot protocol for the synthesis of N-aryl 1,2,3-triazoles from arenes by an iridium-catalyzed CH borylation/copper catalyzed azidation/click sequence is described. 1 mol % of Cu(OTf)2 was found to efficiently catalyze both the azidation and the click reaction. The applicability of this method is demonstrated by the late-stage chemoselective installation of 1,2,3-triazole moiety into unactivated molecules of pharmaceutical importance.

A single-phase high-efficiency near-unity power-factor (PF) half-bridge boost converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. This converter is capable of operating under variable PF. However, the focus of this paper is in achieving unity PF operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two DC-link capacitors, which was noted before, is confirmed here. The cause for the imbalance is analyzed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed-band hysteresis current control (HCC) technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90-V AC input and 300-W 300-V output, the experimental prototype demonstrates an efficiency of 96.23% and a PF of 0.998. This converter, with its relatively high DC-output voltage, is well suited for the 110-V utility supply system. A circuit modification for universal input voltage range operation is also suggested.

A highly efficient solid-phase strategy for assembly of small molecule inhibitors against protein tyrosine phosphatase 1B (PTP1B) is described. The method is highlighted by its simplicity and product purity. A 70-member combinatorial library of analogues of a known PTP1B inhibitor has been synthesized, which upon direct in situ screening revealed a potent inhibitor ( Ki = 7.0 microM) against PTP1B.

Click chemistry is emerging as a powerful tool to elucidate the complex catalytic functions that enzymes perform in the biological system. Recent advances in proteomics heavily rely on the robust, modular and high-throughput platform offered by click chemistry. This minireview focuses on the central role click chemistry has played on the most recent advances in the chemical proteomic research involving the discovery of enzyme inhibitors and enzyme profiling using Activity-Based Probes (ABPs). The strength and benefit of click chemistry and its novel variants, such as the so-called in situ screening using click chemistry have been even more evident recently when this novel chemistry is coupled with high-throughput assay technologies such as microarrays and characterization techniques such as Liquid Chromatography-Mass Spectrometry in Selected Ion Mode (LCMS-SIM) and multidimensional LC-MS. The invaluable contribution of click chemistry in the emerging field of “Catalomics” is thus firmly established.

This protocol describes the step-by-step procedures for the efficient assembly of bidentate inhibitor libraries of a target enzyme, using the so-called 'click chemistry' between an alkyne-bearing core group and an azide-modified peripheral group, followed by direct biological screening for the identification of potential 'hits'. The reaction is highlighted by its modularity, high efficiency (approximately 100% yield in most cases) and tolerance toward many functional groups present in the fragments, as well as biocompatibility (typically carried out in aqueous conditions with small amounts of biocompatible catalysts). The approach consists of three steps: (i) chemical synthesis of alkyne-bearing protein tyrosine phosphatase or matrix metalloprotease core groups and diverse azide-modified peripheral groups; (ii) click chemistry to assemble the bidentate inhibitor libraries; and (iii) direct screening of the libraries with target enzymes using 384-well microplate assays. Following the chemical synthesis of the core and peripheral groups and optimization of the click chemistry conditions (approximately 1 week), steps (ii) and (iii) take 3 d to complete (approximately 1-2 d for library assembly and 1 d for inhibitor screening).

The study of dynamic movement and interactions of proteins inside living cells in real time is critical for a better understanding of cellular mechanisms and functions in molecular detail. Genetically encoded fusions to fluorescent protein(s) (FP) have been widely used for this purpose [Annu. Rev. Biochem. 1998, 67, 509-544]. To obviate some of the drawbacks associated with the use of FPs [Curr. Opin. Biotechnol. 2005, 16, 1-6; Nat. Methods2006, 3, 591-596], we report a small molecule-based approach that exploits the unique reactivity between the cysteine residue at the N-terminus of a target protein and cell-permeable, thioester-based small molecule probes resulting in site-specific, covalent tagging of proteins. This approach has been demonstrated by the in vivo labeling of proteins in both bacterial and mammalian systems thereby making it potentially useful for future bioimaging applications.

[reaction: see text] We have successfully designed and synthesized a small library of protein tyrosine phosphatase (PTP) inhibitors, in which the so-called "click chemistry" or Cu(I)-catalyzed 1,3-dipolar alkyne-azide coupling reaction was carried out for rapid assembly of 66 different bidentate compounds. Subsequent in situ enzymatic screening revealed a potential PTP1B inhibitor (IC(50) = 4.7 microM) which is 10-100 fold more potent than other PTPs.

We have successfully synthesized a number of small molecule probes designed for site-specific labeling of N-terminal cysteine-containing proteins expressed in live cells. Their utility for site-specific, covalent modifications of proteins was successfully demonstrated with purified proteins in vitro, and with live bacterial cells in vivo.

We have successfully synthesized a number of small molecule probes designed for site-specific labeling of N-terminal cysteine-containing proteins expressed in live cells. Their utility for site-specific, covalent modifications of proteins was successfully demonstrated with purified proteins in vitro, and with live bacterial cells in vivo.

A single-phase, high efficiency, and near-unity power factor half-bridge boost power converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. Though this power converter is capable of operating under variable power factor, the focus of this paper is in achieving unity power factor operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two DC link capacitors, which was noted before, is confirmed here. The cause of the imbalance is analysed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed band hysteresis current control technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90 V AC input and 300 W, 300 V output, the experimental prototype demonstrates an efficiency of 96% and a power factor of 0.998. This power converter, with its relatively high DC output voltage, is well suited for 110 V utility supply system. A circuit modification for universal input voltage range operation is also suggested.

A single-phase parallel power processing scheme with input-paralleled power factor correction stage is proposed. The input current in the proposed scheme is nearly-sinusoidal with power factor close to unity. This scheme is very attractive for systems with two or more independent loads, each requiring an AC-DC power converter. An example of one such system is a personal computer (the monitor and the CPU units). For such a system, the proposed scheme is both cost effective and efficient than the popular two-stage cascaded scheme. The scheme is implemented using a half-bride boost PFC stage, and is analysed in detail. Analytical plots and expressions useful to a design engineer, have been developed. Switched and averaged model simulation results, and experimental results are also included. An efficiency of 93.78% at 90 V input, and a power factor of 0.999 were obtained experimentally. The possible circuit variations of the proposed scheme have also been identified.

A single-phase AC-DC buck-type converter using only two switches is studied in detail. The converter is derived from half-bridge boost AC-DC converter using the principle of duality of electrical networks. The converter can be used with various control techniques such as sine PWM and phase control. An inductor voltage control method, capable of fast and robust input current control, is adopted here. With this control the converter can be made to draw a near sinusoidal input current with any arbitrary power factor while the output voltage may be controlled smoothly from a maximum value to zero volts. The proposed converter is analysed in detail, and analytical plots and expressions useful to a design engineer, have been developed. An averaged circuit model of the converter has been developed to obtain the analytical results of some of the circuit variables. This model can also be used successfully for fast and efficient circuit simulation studies. Besides providing the experimental results, the merits and demerits of the converter are also brought out.

With the enforcement of the agency standards such as IEC-555-2 for the harmonic components of the input line current, conventional single phase AC/DC power converters with rectifier-capacitor type input interface can no longer be used in switch mode power supplies except for power levels below 75 W. As a result, several alternative AC/DC converters, called power factor corrected (PFC) converters, meeting the agency requirements have been proposed. Most of these achieve near sinusoidal input current irrespective of power levels. However, for lower power levels, IEC-555-2 does not require a sinusoidal input current. Realising this, a parallel power processing scheme is proposed. Here, a conventional offline converter is paralleled with a PFC converter resulting in less overall power handled and thus in improved efficiency. Excellent output dynamics is achieved by two control methods. Method 1 proposes to cancel the second harmonic (100 Hz) current component injected into the output capacitor by the PFC converter. The input harmonic performance was improved further in method 2 which may be viewed as a modification of method 1. SABER simulation using both switched models and averaged models are utilised to confirm the anticipated good performance of the proposed scheme. >

A key challenge in current drug discovery is the development of high-throughput (HT) amenable chemical reactions that allow rapid synthesis of diverse chemical libraries of enzyme inhibitors. The Cu(I)-catalyzed, 1,3-dipolar cycloaddition between an azide and an alkyne, better known as "click chemistry", is one such method that has received the most attention in recent years. Despite its popularity, there is still a lack of robust and efficient chemical strategies that give access to diverse libraries of azide-containing building blocks (key components in click chemistry). We report herein a highly robust and efficient strategy for high-throughput synthesis of a 325-member azide library. The method is highlighted by its simplicity and product purity. The utility of the library is demonstrated with the subsequent "click" synthesis of the corresponding bidentate inhibitors against PTP1B.

A panel of 198 P4-diversified aldehyde (reversible) and vinyl sulfone (irreversible) inhibitors is successfully synthesized via an efficient "click chemistry" platform and directly screened against caspase-3 and -7 for inhibition.