Chemistry of Modified Cyclodextrins

Various modified CyDs have been prepared to improve their binding affinities and selectivities controlled by external factors such as photons, metal ions, or pH. Such CyDs can act as chemosensors, artificial enzymes, drug carriers, or reaction fields. CyDs have been used as scaffolds for highly preorganizing functional units. There are aheady many reviews on modified CyDs [1-6, 8, 9, 123-125], so here we summarize only developments reported in the last seven years. 

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Modification Reactions of Cyclodextrins and the Chemistry of Modified Cyclodextrins... 

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. 

Ashton, PR, SE Boyd, G Gattuso et al. (1995). A novel approach to the synthesis of some chemically-modified cyclodextrins. The Journal of Organic Chemistry, 60(12), 3898—3903. 

Monflier, E. Blouet, E. Barbaux. Y. Mortreux. A. Wacker oxidation of I-decene to 2-decanone in the presence of a chemically modified cyclodextrin system A happy union of host-guest chemistry and homogeneous catalysis. Angew. Chem.. Int. Ed. 1994. 33. 2100-2102. 

O Mahony et al. modified cyclodextrin structurally, for enhanced siRNA deliveiy to the brain. In this study, an amphiphilic cationic p-cyclodextrin with hydrocarbon chains (C12) on the primacy face and a polar (propyl-amino) group on the secondary face was synthesized by applieation of copper(I)-catalyzed click chemistry. The results showed a signifieant inerease in siRNA delivery, with at least 80% eell viability after modification of cyclodextrin in both immortalized hypothalamic neurons and primary hippocampal neurons. Other physicoehemical properties of modified CDs were also found to be suitable for a gene deliveiy system. On the other hand, an investigation of modified amphiphilic p-cyclodextrin was done by Godinho et al. In this particular study, efficient HTT siRNA delivery with limited toxicity was reported. 

Two reviews (in Japanese) have appeared on aspects of cyclodextin chemistry a) on structure, physical properties, toxicity, metabolism, entrapping characteristics and uses in the pharmaceutical and food industries, and on the construction of chemically modified cyclodextrins that recognize anions. ... 

There has been considerable interest in the development of new methods of chemical sensing to recognize molecules or ions as important application of supramolecular chemistry [1-3]. Our group has prepared many kinds of chro-mophore-modified cyclodextrins (CD) as chemosensors for detecting molecules [4-8]. Colorless neutral molecules can be detected as changes in the intensities of the fluorescence, absorption, or circular dichroism using chemosensors based on chromophore-modified CD. 

Table 9.5 Percentage conversion from allylamine (1.8 mmol) to propylamine obtained with cyclodextrin (CD)-modified Pt and Pd nanoparticles under 1.0 atm H2(g) at room tempera ture in D20 solution (2.0 ml ). (Reprinted with permission of the Royal Society of Chemistry [69])...

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