Introduction
Cyclodextrins (CDs) are cyclic oligosaccharides consist of (α-1,4)-linked α-D-glucopyranose units produced by bacterial digestion of cellulose. These structurally related natural products contain a central cavity that was lined by the skeletal carbons and ethereal oxygens of the glucose residues, which gave it a lipophilic character to a certain extent while the outer surface is hydrophilic. The 3D-structure of CDs are shaped like a truncated cone rather than perfect cylinders due to the chair conformation of their glucopyranose units. The hydroxyl functional groups are orientated on the cone exterior with the primary hydroxyl groups of the sugar residues at the narrow edge of the cone, and the secondary hydroxyl groups at the wider edge. The polarity of the cavity has been estimated to be similar to that of an aqueous
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The use of artificial enzymes could probably increase the scope of enzyme catalysis in synthesis. However, the natural product CD-based oxidases, with ketone as functional group are well known as a good artificial enzyme mimics. These inexpensive, harmless, easily functionalized and water-soluble natural products are commercially available. In addition, the structure of CDs enable them to form host-guest complexes with hydrophobic molecules. As a result, these molecules have been used in a wide range of fields.
In manufacturing cyclodextrins, a reasonable assumption is that the catalytic group is better placed at the secondary rim of CDs since this opening is wider and therefore more likely to bind the substrate. Generally, CDs with one to four aldehyde groups attached to the secondary rim are the most powerful artificial amine oxidase catalysts.
Oxidation of