HPLC resolution of atropoisomeric compounds on a csp derived from (1R;2R)-diaminocyclohexane: Thermodynamic data from variable temperature chromatography

The preparation and a preliminary chromatographic evaluation of a novel polymeric chiral stationary phase (CSP) derived from (1R;2R)-diaminocyclohexane (DACH) are presented. A radical copolymerization process has been employed to generate a silica-based chiral sorbent, showing considerable high chemical and thermal stability and stereoselectivity toward racemic compounds capable of H-bonding (3-hydroxy-benzodiazepin-2-ones, chlorthalidone, atropoisomeric sulfur compounds, etc.); in the present paper we present the investigation on the resolution of racemic dihydroxy biarylic atropoisomers; the effects of eluent composition and of temperature on the separation ability of the CSP have been studied in order to elucidate the recognition mechanism operating in these chiral separations. © 1992 Wiley-Liss, Inc.     

The Enantiomeric Separation of Tetrahydrobenzimidazoles Cyclodextrins‐ and Cyclofructans

High performance liquid chromatography (HPLC) and capillary electrophoresis (CE) were used to examine the enantiomeric separation of a series of 17 racemic tetrahydrobenzimidazole analytes. These compounds were prepared as part of a synthetic program directed towards a select group of pyrrole‐imidazole alkaloids. This group of natural products has a unique framework of pyrrole‐ and guanidine‐containing fused rings which can be constructed through the intermediacy of a tetrahydrobenzimidazole scaffold. Several bonded cyclodextrin‐ (both native and derivatized) and derivatized cyclofructan‐based chiral stationary phases were evaluated for their ability to separate these racemates via HPLC. Similarly, several cyclodextrin derivatives and derivatized cyclofructan were evaluated for their ability to separate this set of chiral compounds via CE. Enantiomeric selectivity was observed for the entire set of racemic compounds using HPLC with resolution values up to 3.0. Among the 12 different CSPs, enantiomeric recognition was most frequently observed with the Cyclobond RN and LARIHC CF6‐P, while the Cyclobond DMP yielded the greatest number of baseline separations. Fifteen of the analytes showed enantiomeric recognition in CE with resolution values as high as 5.0 and hydroxypropyl‐γ‐cyclodextrin was the most effective chiral additive. Chirality 25:133–140, 2013. © 2012 Wiley Periodicals, Inc.     

Separation of Nadolol Stereoisomers by Chiral Liquid Chromatography at Analytical and Preparative Scales

The separation of the four nadolol stereoisomers on Chiralpak® AD by chiral liquid chromatography was carried out at both analytical and preparative scales. A screening of possible mobile‐phase compositions was performed using different alcohol–hydrocarbon mixtures. The results obtained confirm the use of 20:80:0.3 ethanol‐hexane‐diethylamine reported by McCarthy (1994) but introduce other possibilities for the complete resolution of the four nadolol stereoisomers at analytical scale, namely, the mixtures 30–40:70–60:0.3 ethanol‐heptane‐diethylamine. Additionally, this work describes how retention and resolution depend on the ethanol content in hexane and heptane mixtures. The separation of nadolol stereoisomers is also carried out at preparative scale and different alcohol–hydrocarbon compositions are proposed, depending on the target component to be obtained. Particularly, this work presents the experimental separation of the more retained nadolol stereoisomer (RSR‐nadolol) by simulated moving bed (SMB) chromatography using an 80:20:0.3 ethanol‐heptane‐diethylamine mobile phase. For a 2 g/l feed concentration, RSR‐nadolol is 100% recovered at the extract outlet stream, 100% pure, and with a system productivity of 0.65 g_{RSR‐nadolol}/(l_bed^.h) and a solvent consumption of 9.6 l_solvent/g_{RSR‐nadolol}. Chirality 25:197–205, 2013. © 2013 Wiley Periodicals, Inc.     

Magnetic separations in biotechnology

Magnetic separations are probably one of the most versatile separation processes in biotechnology as they are able to purify cells, viruses, proteins and nucleic acids directly from crude samples. The fast and gentle process in combination with its easy scale-up and automation provide unique advantages over other separation techniques. In the midst of this process are the magnetic adsorbents tailored for the envisioned target and whose complex synthesis spans over multiple fields of science. In this context, this article reviews both the synthesis and tailoring of magnetic adsorbents for bioseparations as well as their ultimate application.     

RECENT DEVELOPMENTS IN MEMBRANE-BASED SEPARATIONS IN BIOTECHNOLOGY PROCESSES: REVIEW

Membrane-based separations are the most ubiquitous unit operations in biotech processes. There are several key reasons for this. First, they can be used with a large variety of applications including clarification, concentration, buffer exchange, purification, and sterilization. Second, they are available in a variety of formats, such as depth filtration, ultrafiltration, diafiltration, nanofiltration, reverse osmosis, and microfiltration. Third, they are simple to operate and are generally robust toward normal variations in feed material and operating parameters. Fourth, membrane-based separations typically require lower capital cost when compared to other processing options. As a result of these advantages, a typical biotech process has anywhere from 10 to 20 membrane-based separation steps. In this article we review the major developments that have occurred on this topic with a focus on developments in the last 5 years.     

GSI promotes vincristine-induced apoptosis by enhancing multi-polar spindle formation

Gamma secretase inhibitors (GSI), cell-permeable small-molecule inhibitors of gamma secretase activity, had been originally developed for the treatment of Alzheimer disease. In recent years, it has been exploited in cancer research to inhibit Notch signaling that is aberrantly activated in various cancers. We previously found that GSI could synergize with anti-microtubule agent, vincristine (VCR) in a Notch-independent manner. Here, we delineate the underlying cell cycle-related mechanism using HeLa cells, which have strong mitotic checkpoints. GSI enhanced VCR-induced cell death, although GSI alone did not affect cell viability at all. GSI augmented VCR-induced mitotic arrest in a dose-dependent manner, which was preceded by apoptotic cell death, as shown by an increase in Annexin V-positive and caspase-positive cell population. Furthermore, GSI amplified multi-polar spindle formation triggered by VCR. Altogether, we show the evidence that GSI enhances VCR-induced apoptosis in HeLa cells via multi-polar mitotic spindle formation, independent of Notch signaling. These data suggest that one or more GS substrates, yet to be identified, in a post-GS processed form, may play a role in maintaining functional centrosomes/mitotic spindles. More significantly, the synergistic effect of GSI in combination with VCR could be exploited in clinical setting to improve the efficacy of VCR.     

L-谷氨酰胺生产及分离纯化研究进展

谷氨酰胺是一种条件性必需氨基酸,具有重要的生理作用,是一种极有开发前途的新药.本文对谷氨酰胺的生理作用、应用、生产及分离纯化工艺进行了综述.     

Fluorine: a new element in protein design

Fluorocarbons are quintessentially man-made molecules, fluorine being all but absent from biology. Perfluorinated molecules exhibit novel physicochemical properties that include extreme chemical inertness, thermal stability, and an unusual propensity for phase segregation. The question we and others have sought to answer is to what extent can these properties be engineered into proteins? Here, we review recent studies in which proteins have been designed that incorporate highly fluorinated analogs of hydrophobic amino acids with the aim of creating proteins with novel chemical and biological properties. Fluorination seems to be a general and effective strategy to enhance the stability of proteins, both soluble and membrane bound, against chemical and thermal denaturation, although retaining structure and biological activity. Most studies have focused on small proteins that can be produced by peptide synthesis as synthesis of large proteins containing specifically fluorinated residues remains challenging. However, the development of various biosynthetic methods for introducing noncanonical amino acids into proteins promises to expand the utility of fluorinated amino acids in protein design.     

Link between biological signaling and increased enantioseparations of acids using glycopeptide antibiotics

The vancomycin analog A82846B has been shown to provide excellent selectivity as a chiral recognition agent for some acidic test analytes in capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). In both modes A82846B outperforms vancomycin as a chiral selector. A82846B has enhanced antibacterial activity data in comparison to vancomycin, which is probably due to the increased dimerization constant of over 100 in magnitude in comparison to vancomycin. The link between the electrophoretic and chromatographic separations observed and the biological activity of A82846B is discussed. Dimerization of A82846B in solution was proposed as a theory as to why A82846B gave such enhanced separations for acidic racemates. Further literature and experimental studies support the theory.