Construction and Application of Supramolecular Assembles Having Regulation Systems for Their Activities

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Natural enzymes have mechanisms to control their activities in response to the concentration of substrates, products or other effectors. In contrast, there have not been many reports of artificial enzymes that have mechanisms to control their activities, although many successful artificial enzymes with high catalytic activity or high substrate selectivity have been reported. Thus, an important area of research in the field of supramolecular chemistry is the development of chemical methods to control the activities of artificial enzymes.In this project, we constructed new supramolecular assembles having regulation systems, such as an allosteric system.1) We prepared cyclodextrin dimer (designated βCβH) that has a catalytic site located between two β-cyclodextrins and acts as an artificial hydrolase. βCβH shows homotropic allosteric-like effect.2) Artificial holoenzymes for benzoin condensation were synthesized using thiazolio-appended β-cyclodextrin dimers. The dimer with an L-aspartic acid residue as a linker for connecting two β-cyclodextrin units caused 26-fold acceleration in the benzoin condensation, whereas the dimer with the linker of a L-glutamic acid residue caused only 7-fold acceleration, indicating that the linker length of the dimer is an important factor in this artificial holoenzyme.3) β-cyclodextrin derivatives bearing a benzo-crown moiety at the primary- or secondary-hydroxy side were synthesized for molecular recognition toward tryptophan (Trp) in zwitterionic form. The secondary-hydroxy side modification was preferable to the primary-hydroxy side one for recognition of Trp, because the ammonium cation part of Trp was located at the secondary-hydroxy side of the cyclodextrin.