Cyclodextrins as enzyme models

Catalytical aspects of supramolecular chemistry will be discussed in some detail in the next chapter. In this section only cyclodextrins as enzyme models will be briefly presented. Several examples of cyclodextrins catalytic activity have been reported. The acceleration of the reaction rate upon adding of CDs is... 

In a pioneering work, Breslow and his colleagues have used a-cyclodextrins as enzyme models in the chlorination of anisole and obtained almost exclusive para chlorination1004-1006. Another approach is the application of micellar solutions1007. 

Iglesias, E. (1998) Cyclodextrins as enzyme models in nitrosation and in acid-base-catalyzed reactions of alkyl nitrites, J. Am. Chem. Soc. 120, 13057-13069. 

Cyclodextrins as enzyme models MAKOTO KOMIYAMA" and MYRON L. BENDER ... 

As described above, the most important reason for the increasing attention to cyclodextrins as enzyme models is the formation of inclusion complexes (the substrates are included in the cavities of cyclodextrins). 

However, cyclodextrins as enzyme models suffer from a shortcoming, namely their only catalytic group is the hydroxyl group, which restricts the scope of their applicability. Thus, many attempts have been made to introduce other catalytic functional groups into cyclodextrins. In these modified cyclodextrins, the introduced groups function as catalytic sites and the cavities of cyclodextrins serve as the binding sites for the substrates. 

Recently marked progress was made in cyclodextrin chemistry. In this review we dealt with only the materials relevant to the use of cyclodextrins as enzyme models since it is beyond the scope of this review to cover all the papers in this field. During this decade, many X-ray analyses of cyclodextrin inclusion complexes were made, giving much important information. Readers who are interested in them are recommended to refer to the book on cyclodextrin chemistry [1]. 

The contribution from Iwao Tabushi (Kyoto) was based on his work with chemically-modified cyclodextrins as enzyme models. The asymmetrically bifunctionalised cyclodextrins (3a,3b) were synthesised in order to mimic the aminotransferase activity of Vitamin B5. The A-B regio-isomer (3a) was used to effect the transformation of keto-acids into L-amino acids with 96% ee. The elegance of the system was demonstrated by the fact that the B-A regioisomer (3b) performs the same reaction on keto-acids to give the corresponding D-amino acids acids with identical enantiomeric excesses. 

Cyclophanes has several great advantages in use as enzyme models. First, the design of the preparation of substituted cyclophanes is well established. Second, they are very stable, even more by stable comparison with corresponding cyclodextrins. Moreover, a cyclophane of certain cavity size is readily available. Because of these advantages, cyclophanes attract increasing attention from chemists. 

Cyclodextrins, also called cycloamylases, doughnut-shaped oligosaccharides, have attracted much attention as enzyme models. Although this area of research was surveyed in Volume 23, much subsequent progress in this field through multifunctionalization of cyclodextrin necessitates a new review. This contribution was written by I. Tabushi and Y. Kuroda, active researchers in this area. 

Cyclodextrins can serve as enzyme models because of their stereospecific binding followed by stereospecific reactions [85], Several modifications of CDs, specifically of their primary and secondary hydroxyls as tosylates, methoxylates, allyl ethers and many others have been described. 

SYNTHESIS AND REACTIVITY OF 3-CYCLODEXTRIN-HISTAMINE AS ENZYME MODEL... 

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