Cyclic oligosaccharide cyclodextrin

The cyclic oligosaccharide cyclodextrins and the cychc ohgopeptide vali-nomycin were recognized as naturally occurring host molecules in he 1950s. Pedersen s discovery of crown ether in 1967 opened the door to research on... 

As mentioned above, some naturally occurring cyclic hosts that possess molecular recognition capabilities were known before crown ethers (the first artificial host molecules) were discovered. For example, the cyclic oligopeptide valinomycin and the cyclic oligosaccharide cyclodextrin were found to bind to specific guest molecules. The chemical modification of cyclodextrin was particularly well-researched, and artificially modified cyclodextrins became one of the most important compoimds used in host-guest chemistry. 

A derivatization with acid chlorides is also possible. Amino acids can be derivatized with 9-fluorenylmethyl chloroformate (FMOC) and separated on a CSP with X-cyclodextrin (ChiraDex gamma ), a cyclic oligosaccharide which consists of eight glucose units. 

Cyclic oligosaccharides composed of a single type of oligosaccharide unit may be named semisystematically by citing the prefix cyclo , followed by terms indicating the type of linkage [e.g. malto for a-(l—>4)-linked glucose units], the number of units (e.g. hexa for six) and the termination -ose . The trivial names a-cyclodex-trin (a-CD) for cyclomaltohexaose, (i-cyclodextrin ((i-CD) for cyclomaltoheptaose and y-cyclodextrin (y-CD) for cyclomaltooctaose are well established. 

Cyclodextrins (CDs) are inclusion compounds formed by enzymatic decomposition of starch to the cyclic oligosaccharides containing six to eight... 

Cyclodextrin (CD). An inclusion cyclic oligosaccharide compound containing six to eight glucose units. 

Cylodextrins (CDs) are a class of chiral cyclic oligosaccharides that have molecule-sized cavities. They commonly comprise between six and eight D-glucopyranoside units that are linked via a-l,4-glycosidic links. Their bowl-shaped form is generally represented as a cylindrical funnel by analogy to the calixarenes family. There is a large number of cyclodextrin derivatives in the... 

Host-guest inclusion complexes, 262—263 antibiotic hosts, 231—233 cahxarene hosts, 228—231 chiral crown ether hosts, 213—218 cyclic oligosaccharide hosts, 218—222 cyclodextrin host selectivities, 223/ host molecular size, 221 hnear ohgosaccharide hosts, 222—228 ir- TT stacking interactions, 217 proteic hosts, 231 Human 15-hpoxygenase, 52/... 

Among the best known and most versatile hosts are the various cydodextrins [1,2] of which a-, P- and y-cyclodextrins are the most available. These are cyclic oligosaccharides built up of six, seven, or eight glucopyranose units, respectively. These compounds can be prepared by enzymatic hydrolysis of starch. The undoubtedly most important member of the cyclodextrin family is P-cyclodextrin (P-CD) which has become a cheap and easily available chemical, suitable for large scale applications. Schemes... 

Cyclodextrins are cyclic oligosaccharides made up of several o-glucose units. Depending on the number of units, these doughnut-shaped molecules are able to host different sized molecules or the same molecule with different association... 

In accordance with Emery s retro-hydroxamate ferrichrome, mentioned above, two retro analogs of the linear ferrioxamine G and cyclic desferrioxamine E (129 and 130, respectively) were prepared. The iron-chelating properties were compared to DFO, showing that the linear retro-desferrioxamine G (131) binds iron faster and the cyclic retro desferrioxamine E (132) has improved affinity to iron, compared to the linear DFO. Based on these resnlts, many retro-hydroxamate ferrioxamines were prepared. In a later paper, Akiyama and coworkers reported the attachment of -cyclodextrin, a cyclic oligosaccharide, composed of seven a-D-glucopyranoside units, linked from position 1 to position 4, to linear retro-hydroxamate ferrioxamines (133 and 134), which formed 1 1 iron(III) complexes. Influenced by the chiral -cyclodextrin gronp, 133 and 134 formed A-selective coordination around the metal ion. In addition, Akiyama proposed that the... 

K Kano, Y Tamiya, C Otsuki, T Shimomura, T Ohno, O Hayashida, Y Murakami. Chiral recognition by cyclic oligosaccharides. Enantioselective com-plexation of binaphthyl derivatives with cyclodextrins. Supramol Chem 2 137, 1993. 

Polymerization in P-cyclodextrin (CD) complexes with monomer offers a route to polymerization, as well as other organic reactions, in water without the need for organic solvents [Ritter and Tabatabai, 2002]. P-Cyclodextrins are toms-shaped, cyclic oligosaccharides obtained by degradation of starch. The hydroxyl groups of the glucose repeat unit of CD are located on the outer surface. This makes the outer surface hydrophilic, whereas the inner surface and cavity are hydrophobic. Water-insoluble monomers become solubilized in water when mixed with CD or CD derivatives because the monomers are absorbed into the cavity. This allows polymerization in aqueous, not organic media, with water-soluble initiators. 

Cyclodextrins (sometimes called cycloamyloses) make up a family of cyclic oligosaccharides composed of 5 or more a-D-glucopyranoside units linked 1 —> 4, as in amylose (a fragment of starch), and have been used as activating macrocyclic excipients in nonaqueous biocatalysis. Griebenow et al. observed that lyophilization of methyl-[3-cyclodextrin with subtilisin Carlsberg in a 6 1 weight ratio resulted in a 164-fold rate enhancement in THF for the transesterification rate of sec-phenethyl alcohol with vinyl butyrate (Scheme 3.3) [98]. 

The inclusions and dynamics of various molecules into cyclodextrins, cyclic oligosaccharides generally serving as a hydrophilic cover for the hydrophobic guest, and formations of... 

A similar chiral environment is given by inclusion to cyclodextrins (CDs), cyclic oligosaccharides (3). The outside of the host molecule is hydrophilic and the inside hydrophobic. The diameters of the cavities are approximately 6 (a), 7-8 (j3), and 9-10 A (7), respectively. Reduction of some prochiral ketone-j3-CD complexes with sodium boro-hydride in water gives the alcoholic products in modest ee (Scheme 2) (4). On the other hand, uncomplexed ketones are reduced with a crystalline CD complex of borane-pyridine complex dispersed in water to form the secondary alcohols in up to 90% ee, but in moderate chemical yields. Fair to excellent enantioselection has been achieved in gaseous hydrohalogenation or halogenation of a- or /3-CD complexes of crotonic or methacrylic acid. These reactions may seem attractive but currently require the use of stoichiometric amounts of the host CD molecules. 

Scheme 10 Cyclodextrins as Homologous Cyclic Oligosaccharides Are Highly Symmetrical and Rigid Compounds and Are Ideal Templates for the Construction of, for Example, Hexameric Peptide Assemblies on a-...

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