Cyclic Dextrins Research Articles

Reducing the Unintentional Impact of Triazole Fungicides on Aspergillus fumigatus: Are Cyclodextrins a Solution?

Graphical Abstract Triazoles are among the most widely used fungicides in agriculture, for the protection of materials and crops. Their broad spectrum of action makes them the substances of choice for preventing and curing fungal diseases such as Septoria or Fusarium wilt. However, their spread in the environment can lead to the selection of triazole resistance not only in crop pathogens, but also in non-target organisms, such as a non-phytopathogenic fungus Aspergillus fumigatus. This fungus is an opportunistic human pathogen associated with high mortality in cases of resistance to pharmacological treatments based on triazoles. There is therefore a need to find ways of limiting the unintended impact of fungicides on this pathogen. We describe here the impact of linear (maltodextrin) or cyclic (cyclodextrins, CDs) dextrins and their interaction with two fungicides (difenoconazole and tebuconazole), through measurements of growth in 20 A. fumigatus strains. Three native (α-CD, β-CD and γ-CD) and two modified (hydroxypropyl-β-CD (HP- β-CD) and heptakis-(2,3,6-tri-O-methyl)-β-CD (TRIMEB)) cyclodextrins were used. In each experiment, the minimum inhibitory concentration (MIC) was determined according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) reference method. Microscopical observations were also performed to highlight the effect of the presence of dextrins. HP-β-CD was the most effective cyclic dextrin. It reduced the antifungal activity of triazoles, whereas maltodextrin and α-CD had no effect. Those observations were more investigated thanks to molecular modeling in order to clarify cyclodextrin/fungicide interactions. The use of cyclodextrins is a promising approach for limiting the emergence of resistance to triazole antifungal drugs.

Synthesis of multivalent sialyllactosamine-carrying glyco-nanoparticles with high affinity to the human influenza virus hemagglutinin

A series of multivalent sialoglyco-conjugated nanoparticles were efficiently synthesized by using highly-branched α-glucuronic acid-linked cyclic dextrins (GlcA-HBCD) as a backbone. The sialoglycoside-moieties, with varying degrees of substitution, could be incorporated onto the preformed nanoparticles. These synthesized particles, which are highly soluble in aqueous solution, were shown to have a spherical nanostructure with a diameter of approximately 15nm. The interactions of the sialoglyco-nanoparticles (Neu5Acα2,6LacNAc-GlcA-HBCDs) with human influenza virus strain A/Beijing/262/95 (H1N1) were investigated using a hemagglutination inhibition assay. The sialoglyco-nanoparticle, in which the number of sialic acid substitution is 30, acted as a powerful inhibitor of virus binding activity. We show that both distance and multiplicity of effective ligand-virus formation play important roles in enhancing viral inhibition. Our results indicate that the GlcA-HBCD backbone can be used as a novel spherical nanocluster material for preparing a variety of glyco-nanoparticles to facilitate molecular recognition.

Synthesis of modified cyclic and acyclic dextrins and comparison of their complexation ability.

We compared the complex forming ability of α-, β- and γ-cyclodextrins (α-CD, β-CD and γ-CD) with their open ring analogs. In addition to the native cyclodextrins also modified cyclodextrins and the corresponding maltooligomers, functionalized with neutral 2-hydroxypropyl moieties, were synthesized. A new synthetic route was worked out via bromination, benzylation, deacetylation and debenzylation to obtain the 2-hydroxypropyl maltooligomer counterparts. The complexation properties of non-modified and modified cyclic and acyclic dextrins were studied and compared by photon correlation spectroscopy (PCS) and capillary electrophoresis (CE) using model guest compounds. In some cases cyclodextrins and their open-ring analogs (acyclodextrins) show similar complexation abilities, while with other guests considerably different behavior was observed depending on the molecular dimensions and chemical characteristics of the guests. This was explained by the enhanced flexibility of the non-closed rings. Even the signs of enantiorecognition were observed for the chloropheniramine/hydroxypropyl maltohexaose system. Further studies are planned to help the deeper understanding of the interactions.

Gas‐chromatographic approach to probe the absence of molecular inclusion in enantioseparations by carbohydrates. Investigation of linear dextrins (“acyclodextrins”) as novel chiral stationary phases

Acetylated/silylated maltooligosaccharides with different degrees of oligomerization have been tested as chiral stationary phases for enantioselective gas chromatography. The acyclic dextrin derivatives carrying tert-butyldimethylsilyl groups at the primary hydroxyl sites and acetyl groups at the secondary hydroxyl sites showed an unexpected ability for the enantioseparation of alpha-amino acid derivatives and halogenated compounds, in addition to some underivatized chiral compounds. Some examples of an improved enantioselectivity invoked by the linear CSPs as compared to that of cyclic oligosaccharides are demonstrated in this work. The results highlight the role of the polar external surface of the selector in lieu of the well-established inclusion mechanism of enantiorecognition by cyclic dextrins. Thus, the enantioseparation of chiral compounds on linear dextrin derivatives--devoid of a molecular cavity--sheds a new light on the mechanisms of enantiorecognition by cyclodextrin derivatives. In contrast to cyclodextrins, linear dextrins are readily accessible in both enantiomeric forms.

CymA of Klebsiella oxytoca Outer Membrane: Binding of Cyclodextrins and Study of the Current Noise of the Open Channel

CymA, the outer membrane component of the cyclodextrin (CD) uptake and metabolism system of Klebsiella oxytoca, was reconstituted into lipid bilayer membranes. The channel properties of this unusual porin were studied in detail. The binding of CDs to the channel resulted in its complete block for ion transport. This result allowed the detailed investigation of carbohydrate binding, and the stability constants for the binding of cyclic and linear carbohydrates to the binding site inside the channel were calculated from titration experiments of the membrane conductance with the carbohydrates. Highest stability constant was observed for α-cyclodextrin ( α-CD; K = 32,000 1/M) followed by β-cyclodextrin ( β-CD; K = 1970 1/M) and γ-cyclodextrin ( γ-CD; K = 310 1/M). Linear maltooligosaccharides bound also to CymA but with much smaller stability constants as compared to cyclic ones. The noise of the current through CymA in multi- and single-channel experiments was investigated using fast Fourier transformation. The current through the open channels had a rather high spectral density, which was a Lorentzian function of the frequency up to 2000 Hz. Upon addition of cyclic dextrins to the aqueous phase the spectral density decreased in a dose-dependent manner, which made it impossible to evaluate the binding kinetics. Experiments with single CymA-channels demonstrated the channel is highly asymmetric concerning channel flickers and current noise.

Electrophoretic resolution of monosaccharide enantiomers in borate-oligosaccharide complexation media

Monosaccharide enantiomers have been directly separated by capillary electroplroresis as complexes with borate and linear or cyclic dextrins of the general poly(gly-(1 -4)-α-D-Glu) structure. Their relative electrophoretic migration and their separation selectivity were mainly influenced by the type and concentration of the chiral additive, the concentration of boric acid, and the chemical nature of a fluorescence-tagging (derivatizing) agent. The analytes were detected by laser-induced fluorescence. All sugar enantromers were resolved using β-cyclodextrin as the electrolyte additive. Their migration order could be adjusted by a type of chiral additive, a derivatizing agent, or the surface property (chemical modification) of the separation capillary

Cyclodextrin-aided microbial transformation of aromatic aldehydes by Saccharomyces cerevisiae

Biotransformation of benzaldehyde and vanillin by growing cells of Saccharomyces cerevisiae was performed in an aqueous medium containing either α- or β-cyclodextrin at the same molar concentration as the substrate. The yeast fermentative activity, as reflected by CO2 evolution, and bioconversion to the corresponding alcohols were both faster and greater in the presence of the cyclic dextrins. Clearly, cyclodextrins were shown to significantly alleviate the inhibitory effects of the aromatic aldehydes.

Alpha-amylase of Escherichia coli, mapping and cloning of the structural gene, malS, and identification of its product as a periplasmic protein.

Mal+ lacZ operon fusions, inducible by maltose, were isolated in Escherichia coli, strain MC4100. One fusion strain, SF1707, was analyzed in detail. This fusion did not map in any of the known genes of the malA or malB region, but its expression was under control of malT, the positive regulator gene of the maltose regulon. The gene in which the fusion occurred mapped between xyl and mtl at 80 min on the linkage map and was transcribed clockwise. We define this gene as malS. The malS-lacZ fusion was transferred onto a phage lambda vector and the 5' portion of malS was subcloned into pBR322. The resulting plasmid was used as a probe to identify the intact malS gene in a lambda library of E. coli chromosomal HindIII fragments. The phage that hybridized with the probe contained a 12-kilobase insert. The malS containing portion was subcloned into pBR322 as a 4-kilobase ClaI-HindIII fragment. This plasmid directed the malT and maltose-dependent synthesis of a periplasmic protein of 66,000 apparent molecular weight. The purified enzyme hydrolyzed maltodextrins longer than maltose including cyclic dextrins. The primary products of hydrolysis were glucose, maltose, and maltotriose, even when maltotetraose was used as a substrate. These properties differentiate this periplasmic enzyme from the cytoplasmic amylomaltase and define it as an alpha-amylase.

A simple and specific assay for cyclodextrin transglucosidase

A new assay for the cyclodextrin transglucosidase of Bacillus macerans is presented. It is based upon the ability of the enzyme to couple the cyclic dextrins to substrates to produce linear nonreducing oligosacharides. These saccharides are then hydrolyzed with α-amylase and the reducing sugars released are measured by conventional tests. The utility and precision of the method are demonstrated by determining enzyme kinetic parameters.

FORMATION AND DEGRADATION OF CYCLIC DEXTRINS BY INTRACELLULAR ENZYMES OF BACILLUS MACERANS.

The enzymes of Bacillus macerans that participate in the formation and degradation of Schardinger dextrins were shown to be intracellular. Bacillus macerans amylase converts starch into cyclic dextrins. A newly discovered enzyme, cyclodextrinase, catalyzes the degradation of cyclic dextrins.

The utilization of Schardinger dextrins by the rat

Comparative metabolism studies were made with radioactive starch and cyclic Schardinger dextrins. This paper describes the growth of radioactive potato tubers, the isolation of radioactive starch from the tubers, and the preparation of radioactive α- and β-cyclic dextrins. The radioactive starch and the two cyclic dextrins were administered to rats and the expired C 14O 2 was measured continuously for 17–23 hours. The distribution of residual radioactivity in the individual organs and carcasses of animals fed starch and Schardinger dextrins was determined by standard combustion techniques. The results show that the cyclic dextrins are metabolized, but at a slower initial rate than starch. However, after 24 hours, the total amounts metabolized are about the same. The distribution of radioactivity within the animals is similar to that of starch.