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.

A study of the DIBAL-promoted selective debenzylation of α-cyclodextrin protected with two different benzyl groups

An α-cyclodextrin protected with 2,4-dichlorobenzyl groups on the primary alcohols and ordinary benzyl groups on the secondary alcohols was prepared and subjected to DIBAL (diisobutylaluminum hydride)-promoted selective debenzylation. Debenzylation proceeded by first removing two dichlorobenzyl groups from the 6A,D positions and then removing one or two benzyl groups from the 3A,D positions.

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.

Deoxy sugars. General methods for carbohydrate deoxygenation and glycosidation

Deoxy sugars represent an important class of carbohydrates, present in a large number of biomolecules involved in multiple biological processes. In various antibiotics, antimicrobials, and therapeutic agents the presence of deoxygenated units has been recognized as responsible for biological roles, such as adhesion or great affinity to receptors, or improved efficacy. The characterization of glycosidases and glycosyltranferases requires substrates, inhibitors and analogous compounds. Deoxygenated sugars are useful for carrying out specific studies for these enzymes. Deoxy sugars, analogs of natural substrates, may behave as substrates or inhibitors, or may not interact with the enzyme. They are also important for glycodiversification studies of bioactive natural products and glycobiological processes, which could contribute to discovering new therapeutic agents with greater efficacy by modification or replacement of sugar units. Deoxygenation of carbohydrates is, thus, of great interest and numerous efforts have been dedicated to the development of methods for the reduction of sugar hydroxyl groups. Given that carbohydrates are the most important renewable chemicals and are more oxidized than fossil raw materials, it is also important to have methods to selectively remove oxygen from certain atoms of these renewable raw materials. The different methods for removal of OH groups of carbohydrates and representative or recent applications of them are presented in this chapter. Glycosidic bonds in general, and 2-deoxy glycosidic linkages, are included. It is not the scope of this survey to cover all reports for each specific technique.

Cyanoethylation of cyclodextrin derivatives

The synthesis of novel cyanoethylated cyclodextrin derivatives from previously prepared intermediates is described. It was found the alcohols at the primary face of cyclodextrins readily react to add to acrylonitrile, but similar additions from hydroxyl groups of the secondary face appear to be more difficult. The obtained cyanides could be reduced to form the corresponding amines.

An "against the rules" double bank shot with diisobutylaluminum hydride to allow triple functionalization of α-cyclodextrin

Frustration leads to overreaction: when diametrically opposed regioselective debenzylation is frustrated, an unexpected double debenzylation reaction affords original tetrafunctionalized cyclodextrins in a controlled and efficient manner. A rationale of the reaction is proposed based on a kinetic study.