Large‐Ring Cyclodextrins as Chiral Selectors for Enantiomeric Pharmaceuticals

Large‐ring cyclodextrins (CD) are cyclic glucans composed of 9 or more α‐1,4‐linked glucose units. They are minor side products of bacterial glucanotransferases (CGTases, EC 2.4.1.19) and have previously been available only in very small amounts for studies of their properties in supramolecular complex formation reactions. We engineered a CGTase to synthesize mainly large‐ring CD facilitating their preparation in larger amounts. By reversed phase chromatography, we obtained single CD samples composed of 10 to 12 glucose units (CD10, CD11, and CD12) with a purity of >90 %. Their identity was confirmed by high resolution mass spectrometry and fragmentation analysis. We demonstrated the non‐toxicity of CD10–CD12 for human cell lines by a cell proliferation assay and impedimetric monitoring. We then showed that CD10 and CD11 are efficient chiral selectors for the capillary electrophoretic separation of the enantiomeric pharmaceuticals fluvastatin, mefloquine, carvedilol, and primaquine.     

Strain-Induced “Band Flips” in Cyclodecaamylose and Higher Homologues

The cavity of the larger molecule has less space for guests! Unlike the structure of the smaller annular cyclodextrins, that of the higher homologues of cycloamyloses (CAs) with more than ten glucose units contains a 90° kink between adjacent glucose residues within one half of the molecule and a 180° band flip between adjacent units in different halves (see depicted section of the CA14 structure) to yield butterfly-shaped structures with narrow, groovelike cavities.     

Effect of the reaction temperature on the transglycosylation reactions catalyzed by the cyclodextrin glucanotransferase from Bacillus macerans for the synthesis of large-ring cyclodextrins

The synthesis of cyclodextrins with from 6 to more than 50 glucose units by cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from Bacillus macerans was investigated. Analysis of the synthesized cyclic α-1,4-glucan products showed that a higher yield of large-ring cyclodextrins were obtained with a reaction temperature of 60 °C compared to 40 °C. The yield of large-ring cyclodextrins obtained at 60 °C represented about 50% of the total glucans employed in the reaction. Analysis of the cyclodextrin-forming cyclization reaction and of the coupling reaction of the CGTase resulting in the degradation of mainly the larger cyclic α-1,4-glucans indicated higher rates of the cyclization reaction at 60 °C compared to 40 °C while the opposite was found for the coupling reaction.     

Large Cyclodextrins

The existence of large cyclodextrins, cyclic -D-(1 4) glucans with a degree of polymerisation higher than eight, has been proven during the past decade. A number of 4- -glucanotransferases have been shown to be able to produce large cyclodextrins consisting of up to several hundred glycosyl units, from both amylose and amylopectin. Large cyclodextrins with degree of polymerisation up to 31 have been isolated to purity by use of elaborate purification schemes, enabling studies of their structural and complex forming properties. The solid state structures of the large cyclodextrins with a degree of polymerisation 10, 14 and 26, respectively, have revealed interesting new structural features of this family of molecules. This review summarises the studies of the large cyclodextrins, a varied and highly interesting group of molecules.     

Cyclodextrin functionalization: Simple routes to tailored solubilities and nanoscopic polymer networks

The systematic chemical modification of cyclodextrins (CDs) provides an opportunity to create new substances with novel phase transfer, guest–host, solubility, and network properties. Such materials have several potential applications in polymer science, including free‐volume modifiers, stabilizers or compatibilizers, and scaffolds or templates for synthesizing new materials. In this study, we describe simple, inexpensive, and easy purification one‐pot methods to selectively functionalize CD rings with short‐ and long‐chain alkyl derivatives of varying polarity. Using bifunctional reagents in the same reaction scheme yields CD‐based polymer networks. Particular attention is devoted to solution and solid‐state NMR experiments that reveal the type and extent of functionalization, which may be used to control solubility and swelling. Alkyl chain functionalization may be expressed as the average number of CH₂ units attached per CD ring, the magnitude of which can reach at least 16 and the product still be water soluble, but products become insoluble in water at a value of 32. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

New side-chain poly(methacryl-rotaxanes) bearing cyclodextrins as non-covalently anchored ring components. Chemoenzymatic synthesis and degradation

The chemoenzymatic synthesis of new side-chain polyrotaxanes ( 6 ) bearing non-covalently attached cyclodextrins is described. Starting from 11-methacryloylaminoundecanoic acid, up to 8 units of 12-hydroxylauric acid were condensed in the presence of a lipase from Candida antarctica. They were copolymerized with methyl methacrylate to comb-like polymers ( 4 ) bearing free carboxylic groups at the end of the oligoester side chains. These free carboxylic groups were then condensed chemically with a nucleophilic barrier group, N-(4-aminobutanoyl)-4-triphenylmethylaniline ( 5 ), in the presence of dimethylated β-cyclodextrin, yielding new polyrotaxanes that contain statistically more than 1 ring component per side chain.     

An Extra‐Large‐Pore Zeolite with Intersecting 18‐, 12‐, and 10‐Membered Ring Channels

Zeolites with extra‐large pores have attracted great attention because of their important applications such as in hydrocracking, catalysis, and separation of large molecules. Despite much progress has been made during the past decades, the synthesis of these materials remains a big challenge. A new extra‐large‐pore zeolite NUD‐1 (Nanjing University Du’s group zeolite no. 1) is synthesized by using an approach based on supramolecular self‐assemblies of small aromatic organic cations as structure‐directing agents. NUD‐1 possesses interconnecting 18‐, 12‐, and 10‐membered ring channels, built from the same building units as those of ITQ‐33 and ITQ‐44. There coexist single 3‐membered ring, double‐3‐membered ring and double‐4‐membered ring secondary building units in NUD‐1, which have not been seen in any other zeolites.     

A comparative study of complexation of enalapril with α-, β- and γ-cyclodextrins in aqueous medium: structure elucidation of inclusion complexes using NMR spectroscopic and molecular mechanics methods

Structural studies of complexes of enalapril maleate with α-, β- and γ-cyclodextrins were carried by NMR spectroscopy and computational methods. The formation of complexes of enalapril with all the three cyclodextrins was established by chemical shift changes observed in the cavity protons of cyclodextrins in the presence of enalapril maleate. The stoichiometry of the complexes was determined to be 1:1 by ¹H NMR titrations studies using Scott’s method. Intermolecular cross peaks observed in the 2D ROESY spectra of mixtures of enalapril maleate with three cyclodextrins helped in establishing the probable structures of these inclusion complexes which were supported by molecular mechanics (MM2) studies. Enalapril forms 1:1 inclusion complex with all the studied cyclodextrins through aromatic ring. The mode of approach of aromatic ring to the α-cyclodextrin cavity was found to be different from those of β- and γ-cyclodextrins, which were identical.     

Cyclodextrin Inclusion Compounds in Research and Industry

α-, β-, and γ-Cyclodextrins are cyclic oligosaccharides consisting of six, seven, or eight glucose units, which can be obtained on a large scale from starch. They form inclusion compounds with smaller molecules which fit into their 5—8 Å cavity. These (crystalline) complexes are of interest for scientific research as, contrary to the classical clathrates, they exist in aqueous solution and can be used to study the hydrophobic interactions which are so important in biological systems. Cyclodextrins also serve as models both for polymeric starch and, in the form of their polyiodide complexes, for “blue iodine-starch”. As cyclodextrins catalyze several chemical reactions they and their functionalized derivatives provide useful enzyme models. Cyclodextrins can be used to advantage in the production of pharmaceuticals, pesticides, foodstuffs, and toilet articles—the (micro-encapsulated) active and aromatic substances enclosed within them are protected from the effects of light and atmosphere and can be easily handled and stored in powder from. Substances which are not very soluble in water become more soluble in the presence of cyclodextrins—creams and emulsions can be stabilized, and the growth and yield of grain harvests can be increased. Cyclodextrins can be chemically modified for many different purposes; polymerized cyclodextrin or cyclodextrin bound to a polymer carrier have already been employed in gel inclusion and affinity chromatography.     

Advances in the Use of Cyclodextrins as Chiral Selectors in Capillary Electrokinetic Chromatography: Fundamentals and Applications

Capillary electrokinetic chromatography is generally recognized as a versatile and robust capillary electromigration technique for the separation of enantiomers. In this mode, one or more chiral selectors are added to the background electrolyte acting as pseudostationary phases. Within the various chiral selectors that have been applied to enantioseparations in capillary electrokinetic chromatography, cyclodextrins are by far the most often used selectors because of their versatility, structural variety and commercial availability. This is reflected in the large number of applications of cyclodextrins to analytical enantioseparations that have been reported between January 2012 and July 2016, the period of time covered by this review. Many of these applications cover aspects of life sciences such as drug analysis, bioanalysis or food analysis. Despite the large number of commercially available cyclodextrins, new derivatives have been developed in order to achieve altered enantioselectivities or to further broaden the application range. Cyclodextrins have also been used to demonstrate the validity of theoretical models of electromigration as well as complex formation equilibria in enantioseparations. Finally, recent studies for an understanding of the molecular basis of the chiral recognition between cyclodextrins and the analytes are discussed.

     

Synthesis of cyclodextrin–pyrrole conjugates possessing tuneable carbon linkers

Cyclodextrins are naturally occurring cyclic oligosaccharides consisting of glucose units. The main feature of cyclodextrins is the ability to accommodate various lipophilic compounds in their interior, which determines them to be popular helpers to the mankind. However, there is still a demand for new derivatives for advanced applications. Herein, we report the synthesis of β-cyclodextrin–pyrrole conjugates. Their preparation is based on an amide bond formation or copper(I)-catalysed azide-alkyne cycloaddition between β-cyclodextrin and pyrrole derivatives. The main advantage of the synthetic approach lies in the possibility to attach the substituent in β-position, because polypyrroles possessing a substituent in this position are generally more conductive than the N-substituted ones. Moreover, the presented synthetic route is general and allows tuning the properties (various types of connections and lengths) of a linker. The presented cyclodextrin–pyrrole derivatives thus open the door for new applications in the field of sensors or tissue engineering.     

Effect of ethanol on the synthesis of large-ring cyclodextrins by cyclodextrin glucanotransferases

Cyclodextrin glucanotransferase (EC 2.4.1.19, CGTase) synthesizes cyclodextrins (CD) composed of 6 to more than hundred glucose units from amylose by an intramolecular transglycosylation reaction. The addition of ethanol to the reaction medium resulted in an increase of the yield of large-ring CD obtained with a CGTase from Bacillus sp. BT3-2 and Bacillus macerans. The presence of 15% ethanol in the reaction mixture with the CGTase from Bacillus sp. BT3-2 resulted in a 30% increase of the amounts of CD₁₀–CD₁₃ synthesized after 5 h of reaction. The addition of 20% ethanol increased the yield of CD₁₄–CD₂₁ up to 1000%. The hydrolysis of the large-ring CD by the CGTases was suppressed in the presence of ethanol. The ring-opening coupling cyclization reactions of the CGTase were effected differently by the organic solvent which may contribute to the observed increase of the yield and size of the CD obtained in the synthesis reactions.     

Physicochemical Properties and Complex Formation Abilities of Large-Ring Cyclodextrins

Large-ring cyclodextrins (LR-CD) are cyclic -1,4-glucanscomposed of nine to more than several hundred glucopyranose units. The firstdefinitive evidence for the existence of LR-CD with a degree of polymerization between 9and 13 was reported in 1965. That LR-CD study did not reveal anything that attracted attention. LR-CD with a degree of polymerization between 9 and 31 were isolated andcharacterized during the past decade, and so began to attract considerable attention. This mini-review summarizes the findings of LR-CD with regard to the potentialfor host-guest interactions and corresponding applications.     

Large-scale purification of human granulocyte-macrophage colony-stimulating factor expressed in <Emphasis Type="Italic">Bombyx mori</Emphasis> pupae

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) acts on many different kinds of cells, including monocytes, macrophages, granulocytes, eosinophils, and multipotential stem cells. To explore further explore pharmaceutical action, we expressed hGM-CSF by the Bombyx mori nucleopolyhedrovirus expression system in silkworm pupae. However, purifying recombinant proteins from silkworm pupae on a large scale has been a big challenge. To establish purification methods suitable for mass production, we tried two crude preparation methods: (NH₄)₂SO₄ fractional precipitation and isoelectric precipitation with a combination of gel filtration andion-exchange chromatography. The isoelectric precipitation method was found to be more efficient. With this method, we eventually obtained approx 11.7 mg of 95% pure product from 1000 g of infected silkworm pupae. The recovery of purified protein was greatly increased, by approx 40%, compared with the other method. The biologic activity of this protein was determined up to 9.0×10⁶ colony-forming units/mg in the final purified product.     

环糊精相关的超分子自组装最新进展

对基于环糊精的超分子自组装的最新研究进展作了综述.详细介绍了环糊精为轮、高分子为轴的聚轮烷的制备及其修饰的方法,同时还介绍了无高分子参与的环糊精的超分子自组装高分子化合物的制备.并且对这些超分子在智能材料、生物医药和聚合催化等方面的应用进行了介绍.     

Chemical synthesis of cyclodextrins by using intramolecular glycosylation

An efficient synthesis of cyclodextrins (CDs) by using the intramolecular glycosylation is demonstrated. alpha-CD, an alpha(1-->4)linked hexaglucoside, was prepared via a block condensation of three maltose units. A modified key maltose intermediate as a precursor to both glycosyl donor and acceptor components was prepared in 6 steps starting from maltose. All the glycosylation for chain elongation and cyclization of saccharides was carried out after tethering the donor to the acceptor by the phthaloyl bridge to give the desired saccharides in good yields with complete alpha-selectivity. delta-CD composed of 9 glucose units was synthesized by the same manner from three maltotriose units.     

Production of Large-Ring Cyclodextrins by Amylomaltases

Amylomaltase is a well-known glucan transferase that can produce large ring cyclodextrins (LR-CDs) or so-called cycloamyloses via cyclization reaction. Amylomaltases have been found in several microorganisms and their optimum temperatures are generally around 60–70 °C for thermostable amylomaltases and 30–45 °C for the enzymes from mesophilic bacteria and plants. The optimum pHs for mesophilic amylomaltases are around pH 6.0–7.0, while the thermostable amylomaltases are generally active at more acidic conditions. Size of LR-CDs depends on the source of amylomaltases and the reaction conditions including pH, temperature, incubation time, and substrate. For example, in the case of amylomaltase from Corynebacterium glutamicum, LR-CD productions at alkaline pH or at a long incubation time favored products with a low degree of polymerization. In this review, we explore the synthesis of LR-CDs by amylomaltases, structural information of amylomaltases, as well as current applications of LR-CDs and amylomaltases.     

Azo-Dyes-Grafted Oligosaccharides—From Synthesis to Applications

Azobenzenes are photochromic molecules that possess a large range of applications. Their syntheses are usually simple and fast, and their purifications can be easy to perform. Oligosaccharide is also a wide family of biopolymer constituted of linear chain of saccharides. It can be extracted from biomass, as for cellulose, being the principal constituent of plant cell wall, or it can be enzymatically produced as for cyclodextrins, having properties not far from cellulose. Combining these two materials families can afford interesting applications such as controlled drug-release systems, photochromic liquid crystals, photoresponsive films or even fluorescent indicators. This review will compile the different syntheses of azo-dyes-grafted oligosaccharides, and will show their various applications.     

Aquatic fulvic acid as a matrix for matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric analysis

Aquatic fulvic acids (AFAs) are demonstrated to be effective matrices for the analysis of various polar compounds (ranging from 100–1500 Da) by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). The efficiency of AFA as a matrix is shown for a wide range of test compounds, including a number of carbohydrates, cyclodextrins and peptides, with typical detection limits of ～10 µg mL^?1. The propensity of AFA to enhance ionization through protonation of peptides, and formation of sodium and potassium adducts of carbohydrates and polyethylene glycol, was noted. Differences were observed in the performances of the two AFA matrices used, a Suwannee River, International Humic Substances Society (IHSS) standard and a locally extracted fulvic acid (LFA). For example, in the analysis of carbohydrate standards, the use of the LFA matrix typically doubled the analyte ion signal intensities and resulted in signal‐to‐noise (S/N) ratios that were 2–4 times better than when the Suwannee River AFA matrix was used. AFA was also used in the analysis of real‐world samples without extraction or purification; cantaloupe juice and acetaminophen tablets were analyzed, and glucose and acetaminophen could easily be identified as respective components. When lower concentrations of fulvic acid were used in the presence of sugars, a reversal of roles was observed in which the sugars functioned as the matrix and significantly enhanced ionization of the AFA components, while ions associated with the sugars themselves were suppressed or absent. Effective as a matrix for a variety of analytes and widely available, AFA is an attractive environmentally friendly choice for use in MALDI applications. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of carbohydrate-based azamacrocycles by Richman–Atkins cyclisation

Symmetrical nitrogen containing ring structures with two or four glucose units were easily obtained from accessible monosaccharide building units. Various tetherings via 4,4’- and 6,6’-positions lead to a variety of precursors which were transformed successively employing different bridging units by Richman–Atkins cyclisation to result in defined glycophane coronands.