Intelligent Microflow: Development of Self-Optimizing Reaction Systems

Soft Magnetic Microrobot Doped with Porous Silica for Stability-Enhanced Multimodal Locomotion in a Nonideal Environment

As an emerging field of robotics, magnetic-field-controlled soft microrobot has broad application prospects for its flexibility, locomotion diversity, and remote controllability. Magnetic soft microrobots can perform multimodal locomotion under the control of a magnetic field, which may have potential applications in precision medicine. However, previous research studies mainly focus on new locomotion in a relatively ideal environment, lacking exploration on the ability of magnetic microrobot locomotion to resist external disturbances and proceed in a nonideal environment. Here, a porous silica-doped soft magnetic microrobot is constructed for enhanced stability of multimodal locomotion in the nonideal biological environment. Porous silica spheres are doped into a NdFeB-silicone elastomer base, improving adhesion properties and refining the comprehensive mechanical properties of the microrobot. Multimodal locomotions are achieved, and the influence of porous silica doping on the stability of each locomotion in a nonideal environment is explored in depth. Motions in nonideal circumstances such as climbing, loading, current rushing, wind blowing, and obstacle hindering are conducted successfully with porous silica doping. Such a stability-enhanced multimodal locomotion system can be used in biocatalysis and thrombus removal, and its prospect for precision medicine is highlighted by in vivo demonstration of multimodal locomotion with nonideal disturbance.

Developing flow photo-thiol–ene functionalizations of cinchona alkaloids with an autonomous self-optimizing flow reactor

Continuous flow photo-thiol–ene reactions on cinchona alkaloids with a variety of organic thiols have been developed using enabling technologies such as a self-optimizing flow photochemical reactor.

Automated High-Pressure Atline Analysis of Photo-High-P,T Vitamin D3 Microfluidic Synthesis

Process analytical technology has become a relevant topic in both industry and academia as a mechanism to control process quality by measuring critical parameters; being mainly applied in pharmaceutical industry. An emerging topic is process monitoring with subsequent process automation in flow chemistry using inline, online and atline analyzers. Flow chemistry often deliberately and favorably uses harsh conditions (termed Novel Process Windows) to achieve process intensification which raises the need for sampling under these conditions. This demands for setting in place a stabilization of the sample before exposing it to the processing. Ignoring this may result in being unable to use inline/online analytics and posing the need for a separation step before quantitative analysis, leaving atline analysis as the only feasible option. That means that sampling and connected operations need also to be automated. This is where this study sets in, and this is enabled by a modified high-performance liquid chromatography (HPLC) autosampler coupled to the photo-high-p,T flow synthesis of vitamin D3. It shows that sampling variables, such as decompression speed, can be even more critical in terms of variability of results than process variables such as concentration, pressure, and temperature. The modification enabled the autosampler fully automated and unattended sampling from the reactor and enabled pressure independent measurements with 89% accuracy, >95% reproducibility, and >96% repeatability, stating decompression speed as the primary responsibility for measurements’ uncertainty.

Recent advances in continuous-flow organocatalysis for process intensification

The progresses on continuous-flow organocatalysis from 2016 to early 2020 are reviewed with focus on transition from batch to flow.

Reconfigurable Flow Platform for Automated Reagent Screening and Autonomous Optimization for Bioinspired Lignans Synthesis

Naturally occurring benzoxanthenones, which belong to the vast family of lignans, are promising biologically relevant targets. They are biosynthetically produced by the oxidative dimerization of 2-propenyl phenols. In this manuscript, we disclose a powerful automated flow-based strategy for identifying and optimizing a cobalt-catalyzed oxidizing system for the bioinspired dimerization of 2-propenyl phenols. We designed a reconfigurable flow reactor associating online monitoring and process control instrumentation. Our machine was first configured as an automated screening platform to evaluate a matrix of 4 catalysts (plus the blank) and 5 oxidants (plus the blank) at two different temperatures, resulting in an array of 50 reactions. The automated screening was conducted on micromole scale at a rate of one fully characterized reaction every 26 min. After having identified the most promising cobalt-catalyzed oxidizing system, the automated screening platform was straightforwardly reconfigured to an autonomous self-optimizing flow reactor by implementation of an optimization algorithm in the closed-loop system. The optimization campaign allowed the determination of very effective experimental conditions in a limited number of experiments, which allowed us to prepare the natural products carpanone and polemannone B as well as synthetic analogues.

Scalability of Visible-Light-Induced Nickel Negishi Reactions: A Combination of Flow Photochemistry, Use of Solid Reagents, and In-Line NMR Monitoring

The scale up of light-induced nickel-catalyzed Negishi reactions is reported herein, with output rates reaching multigram quantities per hour. This level of throughput is suitable to support preclinical medicinal chemistry programs in late lead optimization, where tens of grams to hundreds of grams of final product is needed. Adjusting reaction times and concentrations was critical in achieving this robust output. This example demonstrates how visible photochemistry and use of solid metal reagent can be used and how the progress of the reaction can be followed by in-line NMR monitoring.

Flow reactors integrated with in-line monitoring using benchtop NMR spectroscopy

The state-of-the-art flow reactors integrated with in-line benchtop NMR are thoroughly discussed with highlights on the strengths and weaknesses of this emerging technology.

Why microfluidics? Merits and trends in chemical synthesis

The intrinsic limitations of conventional batch synthesis have hindered its applications in both solving classical problems and exploiting new frontiers. Microfluidic technology offers a new platform for chemical synthesis toward either molecules or materials, which has promoted the progress of diverse fields such as organic chemistry, materials science, and biomedicine. In this review, we focus on the improved performance of microreactors in handling various situations, and outline the trend of microfluidic synthesis (microsynthesis, μSyn) from simple microreactors to integrated microsystems. Examples of synthesizing both chemical compounds and micro/nanomaterials show the flexible applications of this approach. We aim to provide strategic guidance for the rational design, fabrication, and integration of microdevices for synthetic use. We critically evaluate the existing challenges and future opportunities associated with this burgeoning field.

Grignard Reagents on a Tab: Direct Magnesium Insertion under Flow Conditions

An on-demand preparation of organomagnesium reagents is presented using a new flow protocol. The risks associated with the activation of magnesium are circumvented by a new on-column initiation procedure. Required amounts of solutions with a precise titration were obtained. Telescoped flow or batch reactions allow access to a diverse set of functional groups.

The route from problem to solution in multistep continuous flow synthesis of pharmaceutical compounds

Recent advances in the field of continuous flow chemistry allow the multistep preparation of complex molecules such as APIs (Active Pharmaceutical Ingredients) in a telescoped manner. Numerous examples of laboratory-scale applications are described, which are pointing towards novel manufacturing processes of pharmaceutical compounds, in accordance with recent regulatory, economical and quality guidances. The chemical and technical knowledge gained during these studies is considerable; nevertheless, connecting several individual chemical transformations and the attached analytics and purification holds hidden traps. In this review, we summarize innovative solutions for these challenges, in order to benefit chemists aiming to exploit flow chemistry systems for the synthesis of biologically active molecules.

Improving the throughput of batch photochemical reactions using flow: Dual photoredox and nickel catalysis in flow for C(sp2)C(sp3) cross-coupling

We report herein the transfer of dual photoredox and nickel catalysis for C(sp²)C(sp³) cross coupling form batch to flow. This new procedure clearly improves the scalability of the previous batch reaction by the reactor's size and operating time reduction, and allows the preparation of interesting compounds for drug discovery in multigram amounts.

On-chip integration of organic synthesis and HPLC/MS analysis for monitoring stereoselective transformations at the micro-scale

We present a microfluidic system, seamlessly integrating microflow and microbatch synthesis with a HPLC/nano-ESI-MS functionality on a single glass chip. The microfluidic approach allows to efficiently steer and dispense sample streams down to the nanoliter-range for studying reactions in quasi real-time. In a proof-of-concept study, the system was applied to explore amino-catalyzed reactions, including asymmetric iminium-catalyzed Friedel-Crafts alkylations in microflow and micro confined reaction vessels.

Self-optimisation of the final stage in the synthesis of EGFR kinase inhibitor AZD9291 using an automated flow reactor

Self-optimising flow reactors combine online analysis with evolutionary feedback algorithms to rapidly achieve optimum conditions.

Online quantitative mass spectrometry for the rapid adaptive optimisation of automated flow reactors

An automated continuous reactor for the synthesis of organic compounds, which uses online mass spectrometry (MS) for reaction monitoring and product quantification, is presented.

Strategic Application of Residence-Time Control in Continuous-Flow Reactors

As a sustainable alternative for conventional batch-based synthetic techniques, the concept of continuous-flow processing has emerged in the synthesis of fine chemicals. Systematic tuning of the residence time, a key parameter of continuous-reaction technology, can govern the outcome of a chemical reaction by determining the reaction rate and the conversion and by influencing the product selectivity. This review furnishes a brief insight into flow reactions in which high chemo- and/or stereoselectivity can be attained by strategic residence-time control and illustrates the importance of the residence time as a crucial parameter in sustainable method development. Such a fine reaction control cannot be performed in conventional batch reaction set-ups.

Microfluidic mixing of nonpolar liquids by contact charge electrophoresis

We present a simple and effective ratcheted microfluidic mixer that uses contact charge electrophoresis (CCEP) of a micron-scale particle to rapidly mix nonpolar liquids. CCEP combines contact charging and electrostatic actuation to drive the continuous oscillatory motion of a conductive particle between two electrodes subject to a constant (DC) voltage. We show how this oscillatory motion can be harnessed to mix laminar flows by using dielectric "ramps" to direct the particle along non-reciprocal, orbital trajectories, which repeatedly stretch and fold the flowing streams. Complete mixing requires that the speed of the particle is much larger than the fluid velocity such that the particle completes many orbits as the fluid flows through the mixing region. The extent of mixing also depends strongly on the size of the particle and the shape of its trajectory; effective mixers relied on larger particles (comparable to the size of the channel) moving along non-reciprocal orbits. While the present study uses mineral oil as a convenient nonpolar liquid, we also screened fifteen common solvents to determine the applicability of CCEP for mixing other organic liquids. Owing to its simple design and low power requirements (~100 nW), the orbital mixer presented here demonstrates the utility and versatility of ratcheted electrostatic actuation in powering active microfluidic operations.

Continuous-flow solid-phase peptide synthesis: a revolutionary reduction of the amino acid excess

A highly efficient continuous-flow technique for the synthesis of peptides was developed. The method allows the application of only 1.5 equivalents of amino acids during coupling, while yielding virtually quantitative conversions. A mesoscale reactor was constructed which permits the use of high temperature and pressure during the synthesis. A complete reaction parameter optimization was carried out. Under the optimum conditions, the couplings of all 20 proteinogenic amino acids were achieved with 1.5 amino acid equivalents with quantitative conversions. As a demonstration of the efficiency of the methodology, difficult sequences and β-peptide foldamers with alicyclic side-chains were synthetized in excellent yields and with lower costs thanks to the lower amounts of amino acid and solvent used. By this the synthesis is highly economic and sustainable. Importantly, exotic and expensive artificial amino acids were incorporated into peptidic sequences by the utilization of a reasonable number of amino acid equivalents. The synthesis can be performed in quantities of microgram to gram in an automated way.

Synthesis of riboflavines, quinoxalinones and benzodiazepines through chemoselective flow based hydrogenations

Robust chemical routes towards valuable bioactive entities such as riboflavines, quinoxalinones and benzodiazepines are described. These make use of modern flow hydrogenation protocols enabling the chemoselective reduction of nitro group containing building blocks in order to rapidly generate the desired amine intermediates in situ. In order to exploit the benefits of continuous processing the individual steps were transformed into a telescoped flow process delivering selected benzodiazepine products on scales of 50 mmol and 120 mmol respectively.

Real-time feedback control using online attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy for continuous flow optimization and process knowledge

The use of automated continuous flow reactors is described, with real-time online Fourier transform infrared spectroscopy (FT-IR) analysis to enable rapid optimization of reaction yield using a self-optimizing feedback algorithm. This technique has been applied to the solvent-free methylation of 1-pentanol with dimethyl carbonate using a γ-alumina catalyst. Calibration of the FT-IR signal was performed using gas chromatography to enable quantification of yield over a wide variety of flow rates and temperatures. The use of FT-IR as a real-time analytical technique resulted in an order of magnitude reduction in the time and materials required compared to previous studies. This permitted a wide exploration of the parameter space to provide process understanding and validation of the optimization algorithms.

Efficient continuous-flow synthesis of novel 1,2,3-triazole-substituted β-aminocyclohexanecarboxylic acid derivatives with gram-scale production

The preparation of novel multi-substituted 1,2,3-triazole-modified β-aminocyclohexanecarboxylic acid derivatives in a simple and efficient continuous-flow procedure is reported. The 1,3-dipolar cycloaddition reactions were performed with copper powder as a readily accessible Cu(I) source. Initially, high reaction rates were achieved under high-pressure/high-temperature conditions. Subsequently, the reaction temperature was lowered to room temperature by the joint use of both basic and acidic additives to improve the safety of the synthesis, as azides were to be handled as unstable reactants. Scale-up experiments were also performed, which led to the achievement of gram-scale production in a safe and straightforward way. The obtained 1,2,3-triazole-substituted β-aminocyclohexanecarboxylates can be regarded as interesting precursors for drugs with possible biological effects.

Novel process windows for enabling, accelerating, and uplifting flow chemistry

Novel Process Windows make use of process conditions that are far from conventional practices. This involves the use of high temperatures, high pressures, high concentrations (solvent-free), new chemical transformations, explosive conditions, and process simplification and integration to boost synthetic chemistry on both the laboratory and production scale. Such harsh reaction conditions can be safely reached in microstructured reactors due to their excellent transport intensification properties. This Review discusses the different routes towards Novel Process Windows and provides several examples for each route grouped into different classes of chemical and process-design intensification.

Segmented flow reactors for nanocrystal synthesis

In the past decade microreactors have emerged as a compelling technology for the highly controlled synthesis of colloidal nanocrystals, offering multiple advantages over conventional batch synthesis methods (including improved levels of control, reproducibility, and automation). Initial work in the field employed simple continuous phase reactors that manipulate miscible streams of a single reagent phase. Recently, however, there has been increasing interest in segmented flow reactors that use an immiscible fluid to divide the reagent phase into discrete slugs or droplets. Key advantages of segmented flow include the elimination of velocity dispersion (a significant cause of polydispersity) and greatly reduced susceptibility to reactor fouling. In this progress report we review the operation of segmented flow microreactors, their application to the controlled synthesis of nanocrystals, and some of the principal challenges that must be addressed before they can become a mainstream technology for the controlled production of nanomaterials.

Alkyne-azide cycloadditions with copper powder in a high-pressure continuous-flow reactor: high-temperature conditions versus the role of additives

A safe and efficient flow-chemistry-based procedure is presented for 1,3-dipolar cycloaddition reactions between organic azides and acetylenes. This simple and inexpensive technique eliminates the need for costly special apparatus and utilizes Cu powder as a plausible Cu(I) source. To maximize the reaction rates, high-pressure/high-temperature conditions are utilized; alternatively, the harsh reaction conditions can be moderated at room temperature by the joint application of basic and acidic additives. A comparison of the performance of these two approaches in a series of model reactions has resulted in the formation of useful 1,4-disubstituted 1,2,3-triazoles in excellent yields. The risks that are associated with the handling of azides are lowered, thanks to the benefits of flow processing, and gram-scale production has been safely implemented. The synthetic capability of this continuous-flow technique is demonstrated by the efficient syntheses of some highly functionalized derivatives of the antifungal cispentacin.

A flow-system array for the discovery and scale up of inorganic clusters

The batch synthesis of inorganic clusters can be both time consuming and limited by a lack of reproducibility. Flow-system approaches, now common in organic synthesis, have not been utilized widely for the synthesis of clusters. Herein we combine an automated flow process with multiple batch crystallizations for the screening and scale up of syntheses of polyoxometalates and manganese-based single-molecule magnets. Scale up of the synthesis of these architectures was achieved by programming a multiple-pump reactor system to vary reaction conditions sequentially, and thus explore a larger parameter space in a shorter time than conventionally possible. Also, the potential for using the array as a discovery tool is demonstrated. Successful conditions for product isolation were identified easily from the array of reactions, and a direct route to 'scale up' was then immediately available simply by continuous application of these flow conditions. In all cases, large quantities of phase-pure material were obtained and the time taken for the discovery, repetition and scale up decreased.

Establishing a flow process to coumarin-8-carbaldehydes as important synthetic scaffolds

Despite their usefulness as fluorophores and synthetic precursors, efficient and reliable routes to coumarin-8-carbaldehydes are lacking. We describe here a high-yielding continuous flow synthesis that requires no manual intermediate purification or work-up, giving access to multigram quantities of the aldehyde product.

On being green: can flow chemistry help?

The principles of Green Chemistry are important but challenging drivers for most modern synthesis programs. To meet these challenges new flow chemistry tools are proving to be very effective by providing improved heat/mass transfer opportunities, lower solvent usage, less waste generation, hazardous compound containment, and the possibility of a 24/7 working regime. This machine-assisted approach can be used to effect repetitive or routine scale-up steps or when combined with reagent and scavenger cartridges, to achieve multi-step synthesis of complex natural products and pharmaceutical agents.

Application of metal-based reagents and catalysts in microstructured flow devices

Over the years, organic synthesis has witnessed several improvements through the development of new chemical transformations or more efficient reagents for known processes. Likewise, technological advances, aiming at speeding up reactions and facilitating their work-up, have established themselves in academic as well as in industrial laboratories. In this Minireview, we highlight very recent developments in flow chemistry, focusing on organometallic reagents and catalysts. First, we describe reactions with homogeneous catalysts immobilized on different support materials using the concept of packed bed reactors. In the last chapter, we will discuss applications that utilize organometallic reagents.