Cyclic oligosaccharides, with

Development of cyclic oligosaccharides with heterogenous linkages 311... 

DEVELOPMENT OF CYCLIC OLIGOSACCHARIDES WITH HETEROGENOUS LINKAGES... 

Cyclodextrins are water-soluble cyclic oligosaccharides with hydrophilic cavities of different sizes. For incorporation of Ceo, thereby facilitating its dissolution in aqueous media, y-CD is the most promising candidate. Molecular modeling (i.e., balancing of cavity radius and fullerene size) suggests that a full inclusion in the... 

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 residue can be named by giving the systematic name of the glycosyl residue, preceded by the linkage type in parentheses, preceded in turn by cyclo- with a multiplicative suffix (i.e. cyclohexakis- etc.)... 

Haworth representation, cyclic monosaccharides, 61-63 Hemiacetal groups disaccharides with, 149-150 without, 148-149 nomenclature, 122-123 oligosaccharides with, 153-154 without, 151-153... 

Table 14 1 /Is. Dn values of permethylated cyclic oligosaccharide hosts with amino acid ester hydrochloride guests...

Cycloamyloses are cyclic oligosaccharides made up of D-glucopyranose rings in a a-1,4 linkage (Fig. 1), Cycloamyloses with six, seven, and eight glucose units have been extensively studied (for review, see 6, 18, 26, 27). 

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]. 

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. 

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