Cyclodextrin modification

Of particular importance for modifications of starch are the enzyme degradation products such as glucose symps, cyclodextrins, maltodextrins, and high fmctose com symps (HFCS). Production of such hydrolysis products requites use of selected starch-degrading enzymes such as a-amylase,... 

Introduction and general overview of cyclodextrin chemistry 98CRV1743. Methods for selective modifications of cydodextrins 98CRV1977. 

There are three main types of CDs a-cyclodextrin (a-CD), -cyclodexlrin (p-CD), and y-cyclodextrin (y-CD), which are macrocycles formed by six, seven, and eight sugar ring molecules, respectively. The spatial structure of p-CD is shown on Fig. 3. Review [19] generalizes data on the synthesis, modification, physicochemical and theoretical investigations of CDs, and certain applications particularly for enantio-separation and pharmaceutical applications. CDs are able to form host-guest complexes (pseudorotaxanes) with hydrophobic molecules such as aza-dyes... 

Some modifications to the cyclodextrin structure have also been found to improve their complexing ability. Casu and coworkers prepared 2,3,6-tri-O-methyl and 2,6-di-O-methyl derivatives of alpha and beta cyclodextrin. They observed that tri-O-methyl-alpha cyclodextrin shows an almost ten-fold increased stability of the complex with the guest, Methyl Orange, compared with the unmodified alpha cyclodextrin. A possible reason for this increase in stability is that the methyl groups are responsible for an extension of the hydrophobic cavity of the cyclodextrin. Other workers,however, observed a much smaller enhancement of stability of complexes on methylation of the cyclodextrin, and a decrease in stability has even been reportedfor the one host-two guests complex of tropaeolin with beta cyclodextrin. Thus, the effect of methylation on the stability of a complex varies with the guest species involved, and cannot be readily predicted. 

Some other interesting modifications of the gamma cyclodextrin structure have been made by the group of Ueno and coworkers. By the... 

Chemical modification of cyclodextrins is achieved through reactions of their hydroxyl groups. Of the 21 hydroxyls ofP-CD, the seven primary ones (C-6) can easily be reacted. In addition, the C-2 secondary hydroxyl groups are also fairly reactive while the ones at C-3 resist modification (e.g. by methylation). Several CD derivatives are available commercially in large quantities including -among others- randomly methylated P-cylodextrin and hydroxypropyl-P-cylodextrin [2]. Chemical modifications substantially alter the solubility of cyclodextrins in water. For example, the solubility of P-CD... 

Attachment of a catalytic unit to the cyclodextrin toms can be achieved by several modifications. One recent example is shown on Scheme 10.3 (although no catalytic application of complexes with this ligand have been disclosed yet), other modified cyclodextrins (126-128) are depicted in Chapter 2. 

Cyclodextrins, products of the degradation of starch by an amylase of Bacillus macerans(1), have been studied in terms of chemical modifications, mainly for the purpose of developing efficient enzyme mimics(2). Not only their unique cyclic structures, but also their ability to form Inclusion complexes with suitable organic molecules, led us to Investigate the total synthesis of this class of molecules(3) We describe here an approach to a total synthesis of alpha(l), gamma(2), and "iso-alpha" cyclodextrin (3). 

Variations of this method are possible in several ways. First of all, cyclodextrin which is available on a large scale by enzymatically catalyzed modification of starch can be tailored by chemical reactions. Furthermore, copolymerizations between different host-guest complexes are possible whereby in some cases the reactivity ratios differ from those reported in literature. 

Scheme S. Stepwise Iooper s walk modification of cyclodextrin.

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