Asymmetric catalysis on sequentially-linked columns.

We report a catalytic asymmetric reaction process that involves the use of solid-phase reagents and catalysts that constitute the packing of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of beta-lactams, to yield pure products with excellent enantio- and diastereoselectivity. We have identified several advantages to conducting chemical reactions on sequential columns, including ease of catalyst and reagent recovery and simplified purification steps that preclude the need for chromatography.     

A flow process for the multi-step synthesis of the alkaloid natural product oxomaritidine: a new paradigm for molecular assembly

A flow process for the multi-step synthesis of the alkaloid natural product (+/-)-oxomaritidine is described, mediated through the use of microfluidic pumping systems that progress material through various packed columns containing immobilized reagents, catalysts, scavengers or catch and release agents; our route involves the combination of seven separate synthetic steps linked into one continuous sequence utilizing flow chemistry.     

Macroporous monolithic poly(4‐vinylbenzyl chloride) columns for organic synthesis facilitation by in situ polymerization of high internal phase emulsions

PolyHIPE materials are produced by polymerizing the continuous phase of emulsions where the internal phase volume fraction is higher than 74%. Columns of flow‐through supports for immobilized scavengers and reagents were prepared by polymerizing the continuous phase of high internal phase emulsions containing 4‐vinylbenzyl chloride and divinylbenzene. Emulsions were placed in containers and polymerized in situ. Highly porous (80% pore volume) monolithic columns with chloromethyl functionalities and crosslinked with divinylbenzene (6% or 40%) were obtained and functionalized by a flow‐through method, immobilizing tris(2‐aminoethyl)amine, diethanolamine, and 4‐bromophenylboronic acid. Columns with immobilized tris(2‐aminoethyl)amine were applied for the effective removal of acid chlorides from the solution pumped through the column. Flow properties (back pressure versus flow rate) were characterized for dichloromethane, N,N‐dimethylformamide and acetonitrile. High effectiveness of columns were demonstrated by an over 90% of acid chloride removal from the solution after a single pass‐flow of the solution through the column. The morphology of the column material was characterized by scanning electron microscopy and showed no damage of the material after the flow‐through utilization. Good permeative properties of the interconnected porous structure make polyHIPE columns good candidates for supports for reagents and catalysts. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6726–6734, 2009     

Automated sample preparation method for suspension arrays using renewable surface separations with multiplexed flow cytometry fluorescence detection

In this paper, we describe a new method of automated sample preparation for multiplexed biological analysis systems that use flow cytometry fluorescence detection. In this approach, color-encoded microspheres derivatized to capture particular biomolecules are temporarily trapped in a renewable surface separation column to enable perfusion with sample and reagents prior to delivery to the detector. This method provides for separation of the biomolecules of interest from other sample matrix components as well as from labeling solutions. After sample preparation, the beads can be released from the renewable surface column and delivered to a flow cytometer for direct on-bead analysis one bead at a time. Using mixtures of color-encoded beads derivatized for various analytes yields suspension arrays for multiplexed analysis. Development of this approach required a new technique for automated capture and release of the color-encoded microspheres within a fluidic system. We developed a method for forming a renewable filter and demonstrate its use for capturing microspheres that are too small to be easily captured in previous flow cells for renewable separation columns. The renewable filter is created by first trapping larger beads in the flow cell, and then smaller beads are captured either within or on top of the bed of larger beads. Both the selective microspheres and filter bed are automatically emplaced and discarded for each sample. A renewable filter created with 19.9 μm beads was used to trap 5.6 μm optically encoded beads with trapping efficiencies of 99%. The larger beads forming the renewable filter did not interfere with the detection of color-encoded 5.6 μm beads by the flow cytometer fluorescence detector. The use of this method was demonstrated with model reactions for a variety of bioanalytical assay types including a one-step capture of a biotinylated label on Lumavidin beads, a two-step sandwich immunoassay, and a one-step DNA binding assay. A preliminary demonstration of multiplexed detection of two analytes using color-encoded beads was also demonstrated. The renewable filter for creating separation columns containing optically encoded beads provides a general platform for coupling renewable surface methods for sample preparation and analyte labeling with flow cytometry detectors for suspension array multiplexed analyses.     

In flow activation of diol-silica with cyanogen bromide and triethylamine for preparing high-performance affinity chromatographic columns

A new coupling strategy using pre-packed diol-silica supports to obtain affinity columns for high-performance affinity chromatography (HPAC) is described. These columns were prepared by "in flow" activation in which solutions containing anhydrous solutions of CNBr and triethylamine are separately pumped to a mixer and then onto a pre-packed diol-silica column. Recycling the amino ligand to be coupled several times over the activated silica diol columns results in ligand immobilization. DNA (the Op 1 lac operator), 6-aminohexyl-Cibacron and a peptide (melittin) were all successfully "in flow" coupled to freshly activated columns. Methods for CNBr activation of pre-packed diol-silica column were developed for one, two or three pump HPLC systems. The supports were successfully used for the HPAC purification of a Lac repressor-beta-galactosidase fusion protein, alcohol dehydrogenase, and calmodulin. Columns prepared by in flow activation/coupling procedures were shown to be stable for at least 14 months. Also, in flow activated silica columns could be stored in anhydrous acetone for at least 3 months prior to coupling. Our experiments with these affinity ligand columns (DNA-silica, aminohexyl-Cibacron F3GA-silica, and melittin-silica), suggests that this is a very successful coupling protocol for producing a variety of HPAC columns.     

Unified gas and supercritical fluid chromatography on 50 μm i.d. Columns

A unified approach to sequential gas and supercritical fluid Chromatography using 50 μm i.d. open tubular columns is described. Sample introduction is performed by means of a rotary injection valve. In order that linear velocities can be optimized independently, a second rotary valve in the chromatographic oven is used to direct the flow of column eluate to the flame ionization detector through either fused silica tubing in GC, or a frit restrictor in SFC. Applications of sequential GC-SFC on a 50 μm i.d. open tubular column are demonstrated, and comparisons made between sequential GC-SFC on 50 and 100 μm i.d. columns.     

Development of solid-phase chemiluminescence immunoassays for digoxin comparing flow injection and sequential injection techniques.

The development of a competitive solid-phase immunoassay for digoxin making use of the acridinium chemiluminescence system is described. Two different instrumental approaches are compared. One is based on a continuous flow system using a peristaltic flow injection analysis pump; the other uses a new sequential injection technique. In both systems a flow cell, consisting of transparent PTFE tubing packed with immobilized antibodies, acts as an immunoreactor. The entire assay, including both the immunoreaction and the chemiluminescence reaction, takes place in this immunoreactor cell. Compared with the flow injection technique, the sequential injection mode showed higher precision, ranging from 2.16 to 5.5% RSD depending on concentration. The total assay time, including regeneration, is less than 8 min with the sequential injection technique. The detection limit for both techniques is in the low femtomole range.     

Column asymmetric catalysis for beta-lactam synthesis

[structure] A catalytic asymmetric reaction process was designed involving the use of solid-phase reagents and catalysts that constitute the packing of a series of "reaction columns". This process was applied to the catalytic asymmetric synthesis of beta-lactams, yielding pure product after crystallization with exceptional enantio- and diastereoselectivity.     

高分子负载贵金属类催化剂及其在有机反应中的最新应用

高分子负载金属催化剂与传统的均相催化剂相比,具有较高的催化活性、立体选择性、较好的稳定性和重复使用性能,并且后处理简单,在反应完成后可方便地借助固-液分离方法将高分子催化剂与反应体系中其他组分分离、再生和重复使用,可降低成本和减少环境污染。本文综述了近五年来高分子负载贵金属类催化剂在有机反应中的最新应用,根据金属不同将其分为钌、钯、银、金四大类,并分类介绍了其在不同固相反应中的应用。本文介绍的负载贵金属类催化剂中的负载物均为不溶性聚合物,但不包括二氧化硅、可溶性聚合物和树枝状大分子等。     

A study of the effects of temperature and pressure on the retention time in series-coupled columns under conditions of constant mass flow rate

The technique of controlling chromatographic selectivity by the adjustment of column temperatures in systems of series-coupled columns is investigated by means of a general model incorporating the effects of temperature and mobile phase compressibility. In a previous article the performance of series-coupled columns was investigated under conditions of constant overall pressure drop. The present paper, on the other hand, considers systems in which a constant mass flow rate is maintained at all temperatures. The expressions derived for the effective partition coefficient and the retention time are compared with those of the previous paper. The numerical results for two-column systems exhibit the same major trends as those for constant pressure drop. It is shown that the effective partition coefficient is slightly dependent on the mass flow rate.     

The effect of temperature and pressure on the retention time in series-coupled gas-chromatographic columns

The promising technique of controlling chromatographic selectivity by the adjustment of individual column temperatures in systems of series-coupled columns is investigated by means of a general model incorporating the effects of temperature and mobile phase compressibility. Expressions are derived for the linear flow velocity, the effective partition coefficient and the retention time for a system of n columns assuming an ideal mobile phase gas, under conditions of constant overall pressure drop and neglect of the temperature dependence of the mobile phase viscosity. The results indicate the importance of thermodynamic parameters, relative to parameters influencing the linear flow velocity, in determining the effect of temperature on the chromatographic retention time. Numerical results are illustrated graphically for two-column systems which are discussed in greater detail. Switching of columns is also discussed and it is shown that even if thermodynamic contributions remain unchanged, non-thermodynamic contributions have a notice-able effect.     

高分子支载手性催化剂在Michael反应中的研究进展

高分子手性催化剂用于不对称有机合成,它易与产物分离、可通过适当的处理后回收重复使用;具有毒性或气味的手性催化剂支载在高分子上后,使用更加安全和方便;而且,适当结构的高分子聚合物可以为不对称反应提供更有利的微环境,提高立体选择性.正是这些优点,高分子手性催化剂的研究越来越受到人们的关注.不对称Michael反应是形成手性碳-碳、碳-杂键的重要反应,在有机合成和药物合成中起着重要的作用.本文综述了近年来的高分子手性催化剂在Michael反应中的应用及最新进展.     

Polymer-supported reagents and catalysts: recent advances in synthetic applications

The current surge in parallel array synthesis for the production of small molecule libraries has generated keen interest in the application of solid-supported reagents and catalysts in solution-phase chemistry. The strategy assimilates the advantages of product isolation and purification of solid-phase organic synthesis with the flexible choice of chemistry from the vast repertoire of solution-phase organic reactions. This review summarizes the significant recent advances in the application of polymer-bound reagents and catalysts in solution-phase synthesis of organic molecules. Multi-step reaction sequences employing sequential use of polymer-supported reagents are also discussed. In view of the earlier review publications on this topic, only the recent literature covering 1998 and 1999 is included.     

微电渗流毛细管原位柱的制备及性能考察

 采用二元致孔剂原位聚合的方法制备了一种新型微电渗流毛细管原位柱。与三元致孔剂制柱方法相比 ,具有制备过程简单、重复性好、能够方便地通过改变致孔剂配比来改变柱床的孔径和孔结构的特点。得到的毛细管柱内部结构均匀 ,通透性好。通过对改变不同致孔剂配比所制备的原位柱的孔结构特征及电渗流情况考察 ,及对柱长和柱径与电渗流的关系的探讨 ,发现制备的原位柱在较高 pH值和较高的有机改性剂浓度条件下 ,电渗流均能保持在较低值 ,可以适应不同电泳分离模式的需要。     

On-line redox derivatization liquid chromatography using double separation columns and one derivatization unit

A new on-line redox derivatization technique using double separation columns and one redox derivatization unit was presented for enhancement of separation selectivity of HPLC. This on-line redox derivatization HPLC system consisted of two separation columns and one redox derivatization unit placed between them. The redox reaction proceeds in the derivatization unit so that an analyte compound migrates as its original form in the first column, while as its oxidized or reduced form in the second column. The retention of the analytes is controlled by the lengths of the two separation columns in this system. We adopted a small column packed with porous graphitic carbon (PGC) as a redox derivatization unit and two C18 silica columns treated with hexadecyltrimethylammonium chloride as separation columns. The redox activity of PGC and the efficiency of the on-line redox derivatization HPLC system for enhancement of separation selectivity were investigated using EDTA complexes of some metal ions. Original untreated PGC and PGC treated with hydrogen peroxide completely oxidized Co(II)-EDTA and converted it to Co(III)-EDTA, while the other metal complexes eluted as their original oxidation states throughout the system. Selective separation and determination of cobalt in a reference copper alloy by the developed method were demonstrated.     

Fluidized beds in flow analysis: use with ion-exchange separation for spectrophotometric determination of zinc in plant digests

A novel strategy for utilization of solid reagents in flow analysis is proposed. Establishment of diffuse and reproducible geometry enables the solid particles to be maintained in constant floating, reflux, and circulating motion inside a mini-chamber. This is efficiently accomplished with pulsed flows, a characteristic of multi-pumping flow systems. Drawbacks inherent in solid-phase packed columns, for example backpressure, preferential pathways, swelling, etc., and some limitations inherent in immobilized reagents are minimised. Spectrophotometric determination of zinc in plants was selected as an application of the technique. Dowex 1-X8 anionic resin was kept freely inside a mini-chamber. Zinc chloro-complexes were adsorbed on the moving particles and derivatization with zincon was performed after elution. Analytical figures of merit and the potential and limitations of the approach are discussed.     

Functionalized Polymers-Emerging Versatile Tools for Solution-Phase Chemistry and Automated Parallel Synthesis

As part of the dramatic changes associated with the need for preparing compound libraries in pharmaceutical and agrochemical research laboratories, industry searches for new technologies that allow for the automation of synthetic processes. Since the pioneering work by Merrifield polymeric supports have been identified to play a key role in this field however, polymer-assisted solution-phase synthesis which utilizes immobilized reagents and catalysts has only recently begun to flourish. Polymer-assisted solution-phase synthesis has various advantages over conventional solution-phase chemistry, such as the ease of separation of the supported species from a reaction mixture by filtration and washing, the opportunity to use an excess of the reagent to force the reaction to completion without causing workup problems, and the adaptability to continuous-flow processes. Various strategies for employing functionalized polymers stoichiometrically have been developed. Apart from reagents that are covalently or ionically attached to the polymeric backbone and which are released into solution in the presence of a suitable substrate, scavenger reagents play an increasingly important role in purifying reaction mixtures. Employing functionalized polymers in solution-phase synthesis has been shown to be extremely useful in automated parallel synthesis and multistep sequences. So far, compound libraries containing as many as 88 members have been generated by using several polymer-bound reagents one after another. Furthermore, it has been demonstrated that complex natural products like the alkaloids (+/-)-oxomaritidine and (+/-)-epimaritidine can be prepared by a sequence of five and six consecutive polymer-assisted steps, respectively, and the potent analgesic compound (+/-)-epibatidine in twelve linear steps ten of which are based on functionalized polymers. These developments reveal the great future prospects of polymer-assisted solution-phase synthesis.     

Automated two-dimensional liquid chromatographic system for mapping proteins in highly complex mixtures.

An automated two-dimensional liquid chromatographic system was developed for systematic protein separations which could serve for analytical mapping and preparative separations of proteins. The system applies the principles of the column-switching technique, and consists of two different columns connected in tandem through an electrical column switching valve, two pumping systems to operate each column independently and a system controller to perform sequential chromatography on the two columns. A protein mixture is applied to the first-dimensional anion-exchange column and is separated by stepwise elution with an increasing sodium chloride concentration. The eluent is introduced directly to the second-dimensional reversed-phase column, and is further separated by gradient elution with an increasing acetonitrile concentration. The two elution stages are synchronized by a computer program. By this system, very complex protein mixtures such as crude cerebellar extracts were resolved reproducibly into ca. 200 peaks within 12 h. The method can be used for the total analysis of proteins in various tissues and cells without complicated premanupulation of samples, and allows the simultaneous analysis of a protein isolated by chromatography. The isolated protein is most suitable for use in the strategy of protein and gene sequence analysis.     

Immobilization of chitosan in sol–gel phases for chiral open-tubular capillary electrochromatography

Three different approaches for immobilizing cross-linked chitosan molecules (CS-s) in sol–gel phases to form chiral OT-CEC capillaries were comparatively investigated in this study. To synthesize column I, a bare capillary was first silanized with triethoxysilane (TEOS) and then reacted with the reaction product of 3-glycidyloxypropyltrimethoxysilane (GTS) and CS-s. Column II was prepared by the silanization of a bare capillary with a mixture of TEOS and GTS silanes followed by reaction with CS-s. To obtain column III, all the reagents, including TEOS, GTS, and CS-s were reacted together in a bare capillary. The SEM images showed that the column I phase consisted of two distinct layers, GTS and TEOS sol–gel films, while column II and III phases were homogeneous phases. By elemental analysis, the chitosan contents of the columns were found to decrease in the order column I > II > III, which corresponded to the order of the electroosmotic mobility values obtained from the measurements of the electroosmotic flow in the columns. The retention factor and the selectivity for the chiral separation of phenylglycine enantiomers in the optimized Tris running buffer (100 mM, pH 7.5) also followed this decreasing order. Besides the strength of the interaction with the immobilized functional chitosan, the hydrophobicity of the column affected the resolution of enantiomeric samples. The hydrophilic alanine sample could only be resolved by column III, but the hydrophobic tryptophan and catechin enantiomers were better separated by columns I and II. A reverse-phase mechanism has been found in the separations. Furthermore, the resolution and analysis time of column I and II phases were superior to the phase simply bonded with molecular chitosan.     

Organic monolith frits encased in polyether ether ketone tubing with improved durability for liquid chromatography

This study introduces a preparation method for polymer‐encased monolith frits with improved durability for liquid chromatography columns. The inner surface of the polyether ether ketone tubing is pretreated with sulfuric acid in the presence of catalysts (vanadium oxide and sodium sulfate). The tubing was rinsed with water and acetone, flushed with nitrogen, and treated with glycidyl methacrylate. After washing, the monolith reaction mixture composed of lauryl methacrylate, ethylene glycol dimethacrylate, initiator, and porogenic solvent was filled in the tubing and subjected to in situ polymerization. The tubing was cut into thin slices and used as frits for microcolumns. To check their durability, the frit slices were placed in a vial and a heavy impact was applied on the vial by a vortex mixer for various periods. The frits made in the presence of catalysts were found to be more durable than those made without catalysts. Furthermore, when the monolith‐incorporated tubing was used as a chromatography column, the column prepared in the presence of catalysts resulted in a better separation efficiency. The separation performance of the columns installed with the polyether ether ketone encased monolith frits was comparable to that of the columns installed with the commercial stainless‐steel screen frits.