Abstract
Laboratory Automation and High-Throughput Chemistry
Automated Synthesis of Oligosaccharides as a Basis for Drug Discovery
Carbohydrates present both potential and problems. Their biological relevance has been recognized, but problems in producing sugars render them a difficult class of compounds to handle in drug discovery efforts. The development of the first automated solid-phase oligosaccharide synthesizer and other methods to prepare defined oligosaccharides rapidly have fundamentally changed this situation. A review by Peter H. Seeberger and Daniel B. Werz describes how quick access to oligosaccharides contributes not only to biological, biochemical, and biophysical investigations but also to drug discovery (Nat. Rev. Drug Discov.
Combinatorial Synthesis of Anti-HIV Agents
Combinatorial chemistry is well recognized as an important tool of drug discovery; the integration of a combinatorial approach with the fundamentals of medicinal chemistry and rational drug design is an ongoing challenge. Compound libraries designed to produce specific inhibitors of therapeutic target proteins generate significant interest in drug discovery research. A review by Dharmarajan Sriram et al. presents a survey of combinatorial synthesis of Human Immunodeficiency Virus (HIV)-1 reverse transcriptase inhibitors, protease inhibitors, HIV-1 function inhibitors such as adsorption inhibitors, CCR5 antagonists, and HIV-1 Tat-tar inhibitors that could be of interest as potential anti-HIV drugs (Comb. Chem. High Throughput Screen.
A Simple Continuous Flow Microwave Reactor
A simple new procedure for microwave-assisted organic synthesis under continuous flow processing is available from Mark C. Bagley et al. for use in a monomodal microwave synthesizer with direct temperature control using the instrument's built-in IR sensor. This design makes optimum use of the standing wave cavity to improve the energy efficiency of microwave-assisted flow reactions. The efficiency of the system is demonstrated with a Fischer-Indole synthesis, a hydrolysis reaction of a chloride to an alcohol, and a Bohlmann–Rahtz pyridine synthesis (J. Org. Chem.
Energy Efficiency in Chemical Reactions: A Comparative Study of Different Reaction Techniques
Although it is difficult to compare the effectiveness of various chemical reaction technologies, the energy required to complete a reaction is one of the most simple methods of comparison. James H. Clark et al. compare the energy consumed by a variety of technologies when preparing 1 mol of a chemical compound. Data are gathered for traditional oil bath, supercritical CO2, and microwave reactors. Two different Suzuki couplings, a Knoevenagel condensation, and a Friedel–Crafts acylation are all compared in both the microwave and oil bath, because this is where the most noticeable differences are observed. Most notable is that an 85-fold reduction in energy demand results when switching from oil bath to microwave reactor with a Suzuki reaction (Org. Proc. Res. Dev.
A High-Throughput Screening Approach for the Determination of Additive Effects in Organozinc Addition Reactions to Aldehydes
The effects of additives in phenylzinc addition reactions to aldehydes using an automated high-throughput screening approach are shared by Stefan Dahmen et al. With 2-bromobenzaldehyde as test substrate and N, N-dibutylnorephedrine as chiral ligand, an improvement of 20% enantiomeric excess (EE) over the catalyzed reaction in the absence of the additive is observed. The described results enable a novel approach toward chiral diarylmethanols using commercially available substrates, reagents, ligands, and fast automated techniques. The reactions are carried out on a high-throughput screening system based on a Tecan Genesis Freedom200 robot equipped with a reaction block capable of performing 96 parallel reactions. Reaction vessels are individually sealed by septa, agitated with magnetic stirring, and flushed with argon using the pipetting arm of the robot. All reactions are run at a concentration of 0.25 mmol/mL at 10 °C (Adv. Synth. Catal.
Solid-Phase Synthesis of a 6-Phenylquinolin-2(1H)-one Library Directed Toward Nuclear Hormone Receptors
Markus Ruda et al. describe the preparation of a library of 6-phenylquinolin-2(1H)-ones using solid-phase parallel synthetic techniques. A key step in the synthesis of the library is a tandem alkylation cleavage in which diversity can be introduced at position 1 simultaneously to the cleavage from the resin. The yields of this step are significantly improved over what was previously reported with the addition of cesium carbonate to scavenge the acid formed during the reaction. The resulting 6-phenylquinolin-2(1H)-one library is screened against a panel of nuclear hormone receptors. Certain members of this library display moderate affinity for several of these receptors, and therefore the authors claim that the 6-phenylquinolin-2(1H)-one core of the library can be considered a privileged structure for nuclear hormone receptors (J. Comb. Chem.
A Practical Flow Reactor for Continuous Organic Photochemistry
Compact flow reactors are constructed and optimized by Malcolm B. Berry and colleagues to perform continuous organic photochemistry on a large scale. The reactors are constructed from commercially available or customized immersion well equipment combined with UV-transparent, solvent-resistant fluoropolymer tubing. The reactors are assessed using a [2 + 2] photocycloaddition and the intramolecular [5 + 2] photocycloaddition of 3,4-dimethyl-1-pent-4-enylpyrrole-2,5-dione to form a bicyclic azepine. The reactors are shown to be capable of producing both products in amounts of several hundred grams in a continuous 24-h processing period. Because of the facile control of irradiation time, the continuous-flow reactor also proves to be superior to a batch reactor for performing a problematic photochemical reaction on a larger scale (J. Org. Chem.
Combinatorial Libraries and the Development of Organic Synthetic Methods. PLS Modeling to Discriminate Between Successful and Failed Reaction Systems
Rolf Carlson and Hanna Gautun describe a combinatorial study in which substrate structure, Lewis acid properties, and solvent properties are varied to explore the Fischer indole synthesis. The number of items in the combinatorial library is 254. Of these, 162 afford the Fischer reaction. It is demonstrated how partial least squares (PLS) modeling can be used to identify critical properties of the reaction systems so that conditions that are favorable for both the reactions and conditions that fail can be identified. Subsequent transformation of the PLS models to response surface models enables the analysis of the reaction system properties in detail (Chemom. Intell. Lab. Syst.,
Performing the Synthesis of a Complex Molecule on Sequentially Linked Columns: Toward the Development of a “Synthesis Machine”
Thomas Lectka et al. report the diastereoselective synthesis of the metalloproteinase inhibitor BMS-275291 that is currently in clinical trials as a cancer treatment via a column-based system. This methodology is complementary to classical automated solid-phase synthesis. Columns are packed with resin-bound reagents and then linked in sequence. In contrast to the traditional solid-phase approach, substrates are introduced in the mobile phase where they build up chemical complexity by percolating through the linked columns, ultimately eluting as the desired product (Org. Lett.
Microfluidic Chip Technology and Microreactor Technology
Effect of Temperature on Solids Mixing in a Bubbling Fluidized Bed Reactor
R. Radmanesh et al. report the effects of temperature on solid mixing in a bubbling fluidized bed reactor (Int. J. Chem. React. Eng.
To investigate the effect of temperature on the fluidization of silica sand particles (Geldat-B) in a bubbling fluidized bed reactor, radioactive particle tracking (RPT) is used. Experiments are carried out at different temperatures (25–400 °C) and superficial gas velocities (0.17–0.75 m/s). The effect of temperature on global mixing is studied in conjunction with the changes found in the dynamics of the ascending and descending phases.
A two-phase countercurrent back-mixing model is used for mixing solids in the fluidized bed of sand particles at high temperatures. The effect of temperature on the phase dynamic shows that more solids are present in the dilute phase at higher temperatures. This, in turn, affects the global mixing of solids in the bed.
The dynamic parameters, that is, ascending and descending velocities of the phases and the fraction of each phase in the bed, were found using the instantaneous position of a tagged particle in the bed of the RPT experiments. The only adjustable parameter when fitting the model to the concentration response from a pulse injection is the exchange coefficient between the phases. Kw is found to be in the range of 0.7–2 s–1 for different experiments. The dynamic changes in the bed indicate that increasing the temperature results in a decrease in the value of Kw.
Microchannel Reactors: Applications and Use in Process Development
An overview of microchannel reactors and their applications is shared by S. V. Gakhale et al. (Int. J. Chem. React. Eng.
Microreactors involve reaction chambers with dimensions typically in the range of micrometers (μm) and volumetric capacities in the range of microliters (μL). The advantages of these reactors are that they allow high temperature or concentration with significant ease of process control and thermal management, because of the possibility of reduced dimensions with small volumes of reaction zone. Furthermore, the reactors make regimes of operation infeasible, and improved performance possible. After a historical overview of the development of microreactors, the authors present a summary of some of the more commonly used microreactor systems with some selected details of their operation and use. These systems can be extremely useful in process development work.
Fabrication methods and new novel designs, especially inorganic substance-using semiconductor processing techniques (photolithography and etching), are explained.
The authors introduce some details of fundamental flow behavior, mixing patterns, rate dynamics, heat and mass transfer, design, modeling, and optimization.
In summary, the microchannel reactors prove to be immensely beneficial because:
High surface area to volume ratio (>200), efficient heat and mass transfer, and fluid mixing allow precision reaction control and ensure quality of product. Easy optimization and scale up of process are possible. The development of safe and stable processes can be achieved with reduced scale-up costs and fewer resources. Less time is required to accomplish reaction conversion. This also reduces degradation of products, side product formation, and enhances yield and selectivity. Problematic chemistry (such as that which involves high exothermicity, unstable or toxic products, or difficult to separate byproducts) can be handled easily. A wide variety of high performance material options and reconfigurable modular flexible designs enable specificity and ease of handling for the multiphase system under consideration.
The features of microchannel reactors help research and development organizations engaged in the development of new processes or products come one step closer to reducing development lead time while ensuring product quality, elimination of byproducts, optimum use of mass and energy resources, and thus the economics of the process.
Aqueous Kolbe–Schmitt Synthesis Using Resorcinol in a Microreactor Laboratory Rig Under High-p, T Conditions
Volker Hessel et al. report on aqueous Kolbe–Schmitt synthesis using resorcinol to yield 2,4-dihydroxy benzoic acid in a microreactor rig. A small-scale plant is equipped initially with one capillary reactor and one microstructured cooler only. During the course of the project, two upgraded versions are constructed by having a microstructured cooler and a microstructured mixer. The chemical protocol is significantly varied compared to standard laboratory operation. Higher temperatures (up to 220 °C) and pressures (up to 74 bar) are used. Reaction time can be shortened by orders of magnitude, from about 2 h to less than 1 min, and in some cases even to seconds. This results in a remarkable increase in the space–time yield by a factor of 440 at best. Productivity is in the L/h range and yields at best 111 g/h product compared to 4 t/a. Some drawbacks of the microreactor operation are also identified and discussed, such as high sensitivity to fouling and delicate regulation of system pressure, leading to partly unstable plant operation (Org. Proc. Res. Dev.
High-Throughput Analytics
High-Throughput Purification of Single Compounds and Libraries
During the past few years, the need for increasing productivity in medicinal chemistry and associated improvements in automated synthesis technologies for compound library production has resulted in a major challenge for compound purification technology and its organization. To meet this challenge at Sanofi-Aventis, Erich von Roedern et al. set up three full-service automated chromatography units. Their goal is to combine high-throughput purification with the high attention to detail afforded by a dedicated purification service. This purification laboratory can purify up to 1000 compounds/week in amounts ranging from 5 to 300 mg, whereas the two service intermediate purification units take 100 samples/week in amounts ranging from 0.3 to 100 g. The technologies consist of normal-phase and reversed-phase chromatography, robotic fraction pooling and reformatting, a bottling system, an automated external solvent supply and removal system, and a customized, high-capacity freeze-dryer. All work processes are linked by an electronic sample registration and tracking system (J. Comb. Chem.
From the Mouse to the Mass Spectrometer: Detection and Differentiation of the Endoproteinase Activities of Botulinum Neurotoxins A–G by Mass Spectrometry
J. Barr and co-workers explore a new procedure for identifying and determining activity of botulinum neurotoxins (BoNTs) by mass spectrometry to replace the standard determination method that typically depends on expensive and time-consuming mouse bioassays (Anal. Chem.
BoNTs as zinc-dependent metalloproteinases cleave specific targets on proteins in the nervous system, so that the resulting cleavage products from each BoNT act as toxin-specific fingerprints. The four synthetic peptide substrates used for Endopep-MS cover the entire scope recognized by BoNTs. After an appropriate incubation period, the resulting cleavage targets are identified and analyzed to differentiate activity-dependent toxin concentrations. Although the analysis of the products by MALDI-TOF MS is faster (less than 30 min for a plate with 192 spots), the increased sensitivity provided by ESI-MS/MS (the detection limit is about 10-fold lower) implies a higher safety level for low-toxin-level serum analysis. Based on the detection of protein cleavage products, the assay also can be adapted to other toxins.
Development of Proton-Transfer Ion Trap-Mass Spectrometry: On-line Detection and Identification of Volatile Organic Compounds in Air
Analyzing complex mixtures of volatile organic compounds (VOCs) is a field of continuing interest for environmental analytics. C. Warneke and co-workers from Aeronomy Laboratory, and R. Fall from Cooperative Institute for Research in Environmental Sciences (both Boulder, CO) present a newly developed instrument that uses proton-transfer ion trap-mass spectrometry (PIT-MS) for online trace gas analysis of VOCs (J. Am. Soc. Mass Spectrom.
The general advantages of gas analysis by proton-transfer reaction-mass spectrometry (PTR-MS) compared with GC–MS are the faster time response, the simultaneous analysis of numerous VOCs without preconcentration or chromatographic separation, and the capability of performing stand-alone measurements. Here, the developed mass spectrometer is equipped with an ion trap-mass spectrometer (IT-MS) for extended performance, and can analyze a range of masses of several 100 Th (Thompson) almost simultaneously. Furthermore, VOCs can be identified by collision-induced dissociation and ion molecule reactions in the IT-MS. The PIT-MS instrument assembly is described in detail and important performance tests are discussed. The still unsolved problem compared to PTR-MS, namely the lower sensitivity (about a factor of 5), is the subject of further investigations.
Bioautomation and Screening
A Magnetic Nanoprobe Technology for Detecting Molecular Interactions in Live Cells
Bioactive natural products are an important source of drug leads, but their modes of action are usually unknown. Identification of their physiological targets is essential for understanding their therapeutic and adverse effects, and is also important in chemical biology where high-throughput screening is used to identify small molecules with a desired phenotype. Technologies to assess the molecular targets of biomolecules in living cells are lacking. Won et al. (Science
MAGIC can be used to detect a variety of biological interactions and protein modifications within live cells in a broad range of tissues and disease states. Use of MAGIC in genome-wide expression screening can identify multiple protein targets of a drug.
Identification of Nitric Oxide Donors by Biomimetic HTS Application
Nitric oxide (NO) is known to be active as a powerful vasodilator. In addition, many other physiological functions of NO have been identified. The diverse biological effects of NO might limit the therapeutic application of NO donors; however, targeted NO delivery can lead to more specific NO-related effects. To identify liver-selective, metabolically activated NO donors with diverse chemical structures, Balogh et al. (Comb. Chem. High Throughput Screen.
Such a chemistry-based screen offers several advantages over conventional biological assays: results are not affected by biological uncertainties, automation friendly assay protocols can be developed more easily, and cost/data point ratios can be improved drastically. For automation of the assay, a Tecan CombiTec automated parallel synthesizer is used, and the assay is carried out in a 96-well-plate format. Methodology is validated by testing known NO donors. Samples are analyzed by LC-MS, and absorption measurements are determined with a Tecan Sunrise microplate reader. In addition, a compound library is screened, and identified hits are validated in chemical and microsomal models.
LIMS and Information Technology
Real Networking Compatibility—Control of an HPLC System by a Standard Web Browser
This article (GIT Laborfachzeitschrift
Overcoming Daunting Business Challenges of a LIMS Migration
This article (eLab