Attachment of cyclodextrin acids to PEGA resin and study of binding with fluorescence microscopy

New methods of modification of α-cyclodextrin

While being some of the oldest supramolecular hosts, cyclodextrins remain very popular as molecular binders in materials, devices, artificial enzymes and more. The popularity is undoubtedly connected to the ready availability, carbohydrate biomass origin, biodegradability and water solubility of the cyclodextrins. Many of these applications require synthetic modification of the cyclodextrin - at the simplest the attachment of a linker - but also often attachment of several functional groups, lids, bridges etc. Here we review state of the art methods of modifying α-cyclodextrin, which include direct modications of unprotected α-cyclodextrin and protection/deprotection method to partially modified cyclodextrins.

One-step synthesis of Ling's tetrol and its conversion into A,D-di-allo-α-cyclodextrin derivatives

2A-F,3B,C,E,F,6B,C,E,F-Tetradeca-O-benzyl-α-cyclodextrin or Ling's tetrol is a unique α-cyclodextrin derivative that is partially protected with specific access points on both rims of the cyclodextrin structure. Ling's tetrol is therefore potentially useful for the synthesis of more complex and sophisticated enzyme models and supramolecular structures. However, the original synthesis gave only 10% yield after a reaction time of 4 days, and a recent improvement that gave 52% yield required two steps and a reaction time in one step of 6 days. Here, a single-step synthesis is reported where Ling's tetrol is obtained in a yield of 59% with a reaction time of 40 hours. 2A-F,3B,C,E,F,6B,C,E,F-Tetradeca-O-benzyl-α-cyclodextrin was subsequently converted into 6A,D-dicarboxy-3A,D-diepi-α-cyclodextrin, 3A,D-dioxo-α-cyclodextrin and 3A,D-diamino-3A,D-dideoxy-3A,D-diepi-α-cyclodextrin. The binding of these compounds to CH4 and CO2 was determined.

Taming of the DIBAL Promoted Debenzylation of α‐Cyclodextrin. Kinetics, Substituent Effects and Efficient Synthesis of Lings Tetrol**

The kinetics of the reaction of perbenzyl α‐cyclodextrin was studied varying the concentration of DIBAL and substrate, and the temperature. The initial debenzylation was found to be 1^st order in substrate and follow the relationship 0.0675+0.179[DIBAL]² with respect to the concentration of DIBAL. The second and the third debenzylation which led to the 3^A,6^A,6^D‐triol (Lings triol) were both found to be 1^st order in substrate concentration and zero order in DIBAL concentration. Longer reaction times with DIBAL in high concentration gave further debenzylation to comparatively complex mixtures containing the 2B,3^A,6^A,6^D‐tetrol and the 3^A,6^A,6^C,6^D‐tetrol. In contrast reaction at 0.1 M DIBAL gave the symmetrical 3^A,6^A,3D,6D‐tetrol (Lings tetrol) in 60 % yield. The effect of chlorine or methyl substitution of the phenyl groups of perbenzyl α‐cyclodextrin was also investigated. Per 4‐chlorobenzyl slowed down the reaction with DIBAL, while 4‐methylbenzyl increased the reaction rate, but still gave the corresponding 6 A‐monool or 6^A,6^D‐diol products. A Hammett reaction constant of −4.9 was found for the first debenzylation showing a high degree of positive charge in the transition state. The per(2,4‐dichlorobenzyl)‐α‐cyclodextrin‐derivative was completely resistant to DIBAL, however upon addition of trimethyl aluminium this derivative also reacted to give the 6^A,6^D‐diol product.