Automation Highlights from Literature

Anti-Selective and Regioselective Aldol Addition of Ketones with Aldehydes Using Mgl₂ as Promoter

Stereoselective syntheses of anti-aldol products from unmodified ethyl ketones are of great interest to organic chemists, especially in the area of natural product synthesis. The first example of a direct aldehyde-ketone coupling using the secondary amine piperidine as a base in the presence of MgI₂ to generate a high selectivity of anti-aldol products from unmodified ethyl ketones in high yield is reported by Han-Xun Wei, Richard L. Jasoni, Huawu Shao, Jiali Hu, and Paul W. Paré (Tetrahedron 2004, 51, 1182911835). The coupling reactions are carried out as a one-pot reaction by mixing the four reaction components at room temperature under the protection of nitrogen gas. In the case of unsymmetrical ketones, an addition is made to the less hindered α-side. In order to obtain reasonable yields in this case, longer reaction times (2 h) and higher MgI₂ loading (1.4 equiv) are needed when piperidine is used as the base for the reaction.

Fe-Pillared Bentonite: An Efficient Catalyst for Sulfonylation of Arenes Using Aryl and Alkyl Sulfonyl Chlorides

Aryl sulfones and sulfoxides are interesting functional groups that possess manifold reactivity for conversion to a variety of organosulfur compounds in the fields of drugs and pharmaceuticals. The common methods for preparing such sulfones include the oxidation of sulfides or sulfonylation of arenes using an aryl sulfonyl halide or an aryl sulfonic acid in the presence of a strong acid catalyst. Although these methods are attractive, inherent disadvantages encountered in the use of conventional soluble acid catalysts are: the generation of large amounts of effluent, the inability to recycle reagents, highly corrosive conditions, and a low selectivity for para/ortho sulfonylated isomers. Furthermore, they are incompatible with numerous functional groups including olefins, amines, and some nitrogen hetero-cycles. D. U. Singh et al. report that Fe-pillared bentonite (Fe-PILC) functions as an extremely efficient catalyst for the sulfonylation of activated, as well as unactivated, carbocyclic aromatic compounds and heterocyclic aromatic compounds (Tetrahedron Lett. 2004, 49, 9079-9082). The catalyst is also found to be easily recyclable. After each cycle, the catalyst only is filtered and activated at 80 °C before using for the next cycle. The authors find the activity of the catalyst unaffected even after three cycles.

Simple Microwave-Assisted Method for the Synthesis of Primary Thioamides from Nitriles

The use of thioamides as building blocks in Hantzsch thiazole synthesis has found applicability in many areas of organic chemistry. Primary thioamides are prepared in excellent yield from the corresponding nitrile by treatment with ammonium sulfide in methanol (Mark C. Bagley et al., Synlett 2004, 14, 2615-2617). The reaction is carried out at room temperature for electron-deficient aromatic nitriles, or under microwave irradiation at 80 °C or 130 °C in 15-30 min for other aromatic and aliphatic nitriles. This procedure avoids the use of gaseous H₂S under high pressure, proceeds in the absence of a base, and provides thioamides usually without the need for chromato-graphic purification and, often, in quantitative yield. For the microwave-assisted reaction of nitriles and ammoniumsul-fide, a self-tunable CEM microwave Discover synthesizer was used (initial power 100 W). The system was cooled using a flow of compressed air.

Controlled Heating with Microwaves in Modern Organic Synthesis

An excellent review on microwave-assisted organic synthesis methods is presented by C. Oliver Kappe (Angew. Chem. 2004, 116, 6408). Special focus is given to transition metal catalyzed reactions, syntheses of heterocycles, and use of microwave-assisted syntheses protocols in combinatorial chemistry and library production.

Microarrays of Tagged Combinatorial Triazine Libraries in the Discovery of Small-Molecule Ligands of Human IgG

A novel and highly diverse tagged triazine library incorporating a triethylene glycol-based linker is synthesized by Shao Q. Yao et al. using an orthogonal combinatorial approach on the solid phase, and covalently immobilized on a glass substrate as a small molecule microarray (SMM). The SMM is screened with a fluorophore conjugated human IgG, and 4 novel binders from a library of 2,688 compounds are identified from the fully spatial addressable array without the need for compound decoding. Using surface plasmon resonance (SPR) analysis, binding seen on the array is confirmed, and a binding constant as low as K_d = 2.02 10-6 M is measured (J. Comb. Chem. 2004, 6, 862).

A Library of Spirooxindoles Based on a Stereoselective Three-Component Coupling Reaction

A collection of structurally complex and chemically diverse small molecules is a useful tool to explore cell circuitry. Stuart L. Schreiber and coworkers report the split-pool synthesis of more than 3,000 spirooxindoles on high-capacity macro-beads. The key reaction to assemble the spirooxindole core stereoselectively is a Lewis acid variant of the Williams' three-component coupling. After formation, the skeleton is elaborated using Sonogashira couplings, amide-forming reactions, and N-acylations of γ-lactams. The final library is analyzed by sampling individual macrobeads and by using binomial confidence limits. It is determined that at least 82% of the library compounds should have better than 80% purity. To demonstrate the utility of their discovery process, a high-throughput chemical genetic modifier screen is performed using stock solutions of the resultant products. A number of positives are identified as enhancers of the cellular actions of latrunculin B, an actin polymerization inhibitor. Through resynthesis, the authors confirm one of the positives and demonstrate that in yeast cells, it has an EC₅₀ in the sub-micromolar range (J. Am. Chem. Soc. 2004, 126, 16077).

Parallel Screening of Homogeneous Copper Catalysts for the Oxidation of Benzylic Alcohols with Molecular Oxygen in Aqueous Solutions

A simple and efficient parallel screening method to evaluate the catalytic activities of homogeneous copper complexes for the oxidation of benzylic alcohols in aqueous solutions with molecular oxygen is reported by T. Repo et al. (J. Comb. Chem. 2004, 6, 967-973). Copper(II) sulfate is treated in situ with 22 nitrogen donor ligands, and the catalytic activities of these combinations are studied at four different pH values with two substrates (benzyl alcohol and 3,4-dimethoxy benzyl alcohol), resulting in 176 oxidation experiments in the primary screening stage. Copper complexes based on N,N,N′,N′-tetramethyl ethylenediamine (TMEDA), 9,10-diaminephenanthrene (DAPHEN), and 1,2-diaminocyclohexane (DACH) are determined to be the most active catalysts. In the second screenings, the influence of reaction conditions on Cu(DACH)-, Cu(TMEDA)-, and Cu(DAPHEN)-catalyzed reactions are investigated in more detail. It is found that highly basic reaction conditions favor the reaction with the exception of Cu(TMEDA), which is active at a lower pH range. Under optimized conditions, Cu(DAPHEN) catalyzes the transformation of veratryl alcohol to the corresponding aldehyde with 100% conversion. The screening setup for these experiments is described.

Reactor Cartridge for the Parallel Testing of Homogeneous Catalysts

J. Albers et al. describe the construction and applications of a new reactor cartridge for testing homogeneous catalysts in autoclaves (Chemie Ingenieur Technik 2004, 11, 1672-1675). The major disadvantage of autoclaves is the limited parallelism, usually only one reaction per time unit is supported. The use of the authors' reactor eliminates this disadvantage. It consists of high-grade steel and can be inserted into arbitrary single autoclaves. In principle, the cartridge divides the existing single autoclave area into several reactors that are gastight against each other. The number of chambers is determined by the size of the existing single autoclave. The gas supply is realized after insertion of the module via pressurization of the autoclave. The chamber valve opens automatically at this point, and the pressure balance between the chambers and autoclave is realized. After reconciliation, the valve closes again. The positioning of the autoclave on a heated magnetic agitator enables the thermal energy input and homogenization of the substances in the chambers. For this, each of the chambers contain a standardized magnetic ball. The system permits various modes of operation, for example, isochor and isobar. The chamber module is tested in several applications and represents a simple and inexpensive reactor system that can be inserted into existing laboratory autoclaves.

New Developments in the Field of Reaction Technology: The Multiparallel Reactor HPMR 50-96

The progress in automated reaction technology is marked by the continuous development and the miniaturization of reaction setups. The most important reasons for this development are, on the one hand, the reduction of the amount of used substances (and consequently experimentation costs), and on the other hand, the possibility of increasing throughput (and therefore reducing research costs). A robot integrated multiparallel reaction system, originally intended for catalytic pressure reactions, is described by Allwardt et al. (Chemie Ingenieur Technik 2004, 11, 1679-1682). A glass microtiter plate (Zinsser Analytik) with 96 wells is used as a reaction chamber. The reaction chamber must be airight and watertight to avoid cross contamination. This is achieved through the use of a sealing material (Santropene). The pressure chamber, which is made of Inconnel 625, represents the central structural unit of the reactor system, where the microtiter plate can be placed for the reaction. Pressures up to 50 bar can be realized within the reaction chamber. The desired robotic integration of the system is guaranteed by the bifurcation of the chamber into a movable lid and a static bottom half. The homogenization of the reaction mixture is achieved through the use of a mixing system based on an outer magnetic field. The temperature of the reaction chamber can be varied within the range of 0-100 °C using six peltier elements.

The system HPMR 50-96 has been tested for the hydrogenation of Benzoin. The potential applications of the reactor are not limited to catalytic high-pressure reactions; the system can also be used for different tasks in the field of synthesis optimization or combinatorial chemistry. Future research projects include the expansion of the system to allow parallel treatments of up to 384 tests and the increase of the possible pressure ranges.

Catalyst Surface Characterization in Microfabricated Reactors Using Pulse Chemisorption

The applicability of micoreactors for high-throughput catalyst characterization with quantitative comparison is described by Klavs F. Jensen et al. (ChemCom 2004, 26102611). Today, silicon microfabrication methods allow cost-efficient replication of small chemical reactors with integrated sensors and actuators for automated high-throughput screening. These reactors can be used to accurately and reproducibly measure catalytic rates and selectivities. To compare the activity of supported metal catalysts within a combinatorial library, the number of available surface metal sites is required. With the used pulse CO chemisorption as the quantification method, the adsorbent quantity can be accurately proportioned for small catalyst samples. A wide variety of catalyst properties can be analyzed using this method, depending on the adsorbent molecule and conditions. The microreactors used in this work are fabricated out of silicon and glass substrates. This study demonstrates that quantitative analysis of metal surface sites in supported catalysts is possible using mg quantities of sample in microchemical systems. It can be shown that microreactors are applicable for intelligent high-throughput characterization and materials screening using turnover rates. Pulse measurement approaches are also pertinent for activity and deactivation assessment of the performance of small catalyst samples in microreactors. Analysis of even smaller catalyst masses appears to be possible using online detectors with lowest (ppb) sensitivity. Improved packaging for higher temperature analysis and temperature programmed studies will improve the data precision.

Cation Pool-Initiated Controlled/Living Polymerization Using Microsystems

The discovery of controlled/living polymerization is an epoch-making event in polymer science and technology, and the control of molecular weight and molecular weight distribution is still at the forefront in this field. One of the key issues of controlled/living cationic and radical polymerizations is the establishment of a dynamic equilibrium between active (growing) and dormant species to maintain a low concentration of active species. This equilibrium is also helpful in preventing chain-breaking processes such as termination and transfer reactions. Jun-ichi Yoshida et al. demonstrate the potential of microsystems, in conjunction with their cation pool, to effect cationic polymerization in a highly controlled manner without the deceleration inherent in the dynamic equilibrium between active and dormant species. The molecular weight distribution can be controlled by extremely fast micromixing, and the polymer end can be used as the living reactive species for a follow-up reaction (J. Am. Chem. Soc. 2004, 126, 14702).

Solid-Supported Continuous Flow Synthesis in Microreactors Using Electroosmotic Flow

Paul Watts and Nikzad Nikbin report the fabrication of a microreactor suitable for use with supported reagents. They demonstrate that the electroosmotic flow can be used to move the reagents over a solid-supported catalyst bed. To obtain reproducible flow, it is important that the support does not swell in organic solvents, and it is shown that silica supports fulfill this criteria. Silica-functionalized piperazine is used in a variety of Knoevenagel reactions to enable high conversion of the product (Organic Process Res. Dev. 2004, 8, 942).

Laboratory Information Management Systems for Life Science Applications

Kerstin Thurow and colleagues discuss different aspects of laboratory information management systems in life science applications. Although different LIM systems are available on the market, the state-of-the-art LIMS do not fulfill all requirements regarding flexibity and process connectivity. A fully Web-oriented LIM system is described. The approach presents a system's model based on modern Web-oriented software technologies. It includes planning tools, a virtualized lab, and online process adaptation, as well as an interface for computational data processing and data mining (Organic Process Res. Dev. 2004, 8, 970).

High-Throughput Experimentation in Pharmaceutical Process R&D: Developing a New Software Workflow to Overcome Downstream Data-Analysis Bottlenecks and Improve Productivity

A new software workflow is described by Paul D. Higginson and Neal W. Sach to overcome data analysis, data modification, and visualization bottlenecks. Through a combination of in-house and external supplier expertise, a software workflow tackles the mass of data generated from high-throughput experimentation. Also described is a solution to high-throughput HPLC reaction analysis. In overcoming these bottlenecks, the productivity of their reaction screening technology increased dramatically (Organic Process Res. Dev. 2004, 8, 1009).

Preparative LC-MS Purification: Improved Compound-Specific Method Optimization

One of the remaining challenges in providing effective preparative LC-MS purification is balancing throughput and compound purity. Karl F. Blom et al. (J. Comb. Chem. 2004, 6, 874) describe an approach to optimizing preparative LC-MS methods that provide significantly better chromato-graphic resolution and better compound purity than generic preparative LC methods in the same amount of time. Their approach is easier to implement, is more rugged, and permits significantly greater flexibility than previously reported approaches. The instrument configurations and protocols are specifically tailored for open access support, but the basic approach is equally suitable and effective in high-throughput situations.

Drugs as Materials: Valuing Physical Forms in Drug Discovery

In an excellent review, Colin R. Gardner, Christopher T. Walsh, and Örn Almarsson discuss the challenge of pharmaceutical materials discovery and suggest strategies for addressing the characterization and evaluation of physico-chemical and material properties in the drug discovery and development process (Nature Reviews Drug Discovery 2004, 3, 926). High-throughput platforms for crystallization and formulation also are described.

A Sensitive Colorimetric Method for the Study of Polystyrene Merrifield Resins and Chloromethylated Macroporous Monolithic Polymers

Reactive polymers have attracted great interest due to their application in the development of supported reagents and catalysts, and for the parallel synthesis of chemical libraries. One basic limitation in this area is the proper monitoring of progress of the solid-phase supported reactions. Colorimetric methods are growing in popularity because they are fast and do not require expensive instrumentation. Santiago V. Luis et al. (J. Comb. Chem. 2004, 6, 859) describe a colorimetric methodology based on the reaction of 4-(4-nitrobenzyl)pyridine (NBP) for the detection of chloromethyl groups in polystyrene-based resins. This sensitive test can be applied both for the analysis of individual samples and in combinatorial approaches for the fast optimization of the preparation conditions for resins, obtained by polymerization and reaction conditions for processes involving chloromethylated polymers.

Resonant Multisensor System for High-Throughput Determinations of Solvent/Polymer Interactions

Solvent-resistant polymers are important in numerous research, engineering, and consumer applications. To address the limitations of existing methods of evaluation of polymer solubility and solvent resistance, R. A. Potyrailo et al. (J. Comb. Chem. 2004, 6, 869). develop and build a 6 × 4 array of resonant acoustic-wave sensors operating in the thickness shear mode (TSM). The application of this system makes possible analysis of nanogram quantities of polymers in small amounts of solvent and permits the simultaneous analysis of multiple samples, such as those produced in combinatorial polymerization reactions. These parallel determinations of polymer/solvent interactions eliminate errors associated with serial determinations. During periodic exposure of the TSM crystals to polymer/solvent combinations, the mass increase of the crystal is determined, and is proportional to the amount of polymer dissolved and deposited onto the sensor from a polymer solution. The high mass sensitivity of the resonant TSM sensors (10 ng), use of only a minute volume of solvent (<2 mL), and parallel operation (matching a layout of available 24-well plates) make this system a good fit with available polymer combinatorial synthesis equipment.

High-Throughput Characterization of Materials by Photoluminescence Spectroscopy

An automated system for high-throughput characterization of large libraries of solid materials by photolumines-cence spectroscopy is described by Avelino Corma et al. (Chem. Eur—J. 2004, 10, 6043). The system provides time-resolved transient emission spectra in the microsecond scale and can be employed for characterization of materials of interest in the fields of catalysis and electroluminescence, and others.

A Generally Applicable, High-Throughput Screening-Compatible Assay to Identify, Evaluate, and Optimize Antimicrobial Agents for Drug Therapy

Efficacious and tolerable drugs are needed for successful medication in the clinic. The common preclinical screening cascade in drug discovery focuses on therapeutic activity, and the safety profile is analyzed at a later stage of drug development. Kleymann and Werling (J. Biomol. Screen. 2004, 9, 578) describe a fluorescence-based test system that monitors tolerability of antimicrobial agents simultaneously to their antimicrobial activity in a single assay setup. This novel approach analyzes the survival of host cells in a cell culture experiment infected with microbes, such as viruses, bacteria, or fungi. The authors report that this assay is a generally applicable HTS-compatible test enabling discovery and evaluation of tolerable antimicrobial agents by covering all potential in vitro targets of the pathogen and the host cells simultaneously and speeds up the selection of suitable development candidates. This assay principle could serve as a new standard in anti-infective drug discovery and clinical development.

Development of the “Cell Chip”: A New in Vitro Alternative Technique for Immunotoxicity Testing

The immune system consists of a very sensitive and specific network of cellular and humoral interactions. Deregulation of this system, for instance by xenobiotic exposure, leads to different pathological manifestations. Predictive testing of immunotoxicity is complicated and cannot be accomplished with a single test. Most of the existing tests for immunotoxicity employ experimental animals and rely on a combination of in vivo, ex vivo, and in vitro assays. Ulleras et al. (Toxicology 2005, 206, 245) present a new alternative system for in vitro immunotoxicity testing, which employs changes in cytokine expression observed in vitro as an endpoint, indicating potential for perturbation of the immune system in vivo. This system, named “fluorescent cell chip” (FCC), is based on a number of genetically modified immortalized cell lines representing different phenotypes. This method is suitable for uniform high-throughput testing of xenobiotics and generates information about the changes in expression of cytokines in immune and nonimmune cells exposed in vitro to tested compounds.

High-Throughput Protein Crystallography and Drug Discovery

In a tutorial review, Ian Tickle and colleagues (Chem. Soc. Rev. 2004, 33, 558) cover the various technologies involved in the process pipeline for high-throughput protein crystallography as it is currently being applied to modern drug discovery. Single crystal X-ray diffraction is the technique of choice for studying the interactions of small organic molecules with proteins by determining their three-dimensional structures. The requirement for highly purified protein and the lack of process automation have traditionally limited its use in this field. Despite these shortcomings, the use of crystal structures of therapeutically relevant drug targets in pharmaceutical research has increased significantly over the last decade. The application of structure-based drug design has resulted in several marketed drugs and is now an established discipline in most pharmaceutical companies.

Multidimensional Drug Profiling by Automated Microscopy

Zachary E. Perlman et al. present a method for high-throughput cytological profiling by microscopy. The system provides quantitative multidimensional measures of individual cell states over wide ranges of perturbations. Dose-dependent phenotypic effects of drugs can be profiled in human cell culture with a titration-invariant similarity score (TISS). This method successfully categorizes blinded drugs and suggested targets for drugs of uncertain mechanism. Multivariate single-cell analysis is a starting point for identifying relationships among drug effects at a systems level, and a step toward phenotypic profiling at the single-cell level. This method will be useful for discovering the mechanism and predicting the toxicity of new drugs (Science 2004, 306, 1194).