Short Synthesis of Skeleton-Modified Cyclodextrin Derivatives with Unique Inclusion Ability

Selective modifications at the different positions of cyclodextrins: a review of strategies

Cyclodextrins (CDs) are natural, nontoxic, and biodegradable macrocyclic oligosaccharides. As supramolecular hosts, CDs have numerous applications in many aspects. However, nonsubstituted CDs have the disadvantages of solubility, unspecific recognition sites, and weak interactions with guest molecules. Therefore, new CD-based derivatives are successfully designed, synthesized, and widely used in various fields. This contribution outlines the research progress in CD derivatives. In particular, this review emphasizes the synthesis and application of CDs modified through functionalization in definite positions, random substitution, and reconstruction of the skeleton. At the end of this review, a summary and future directions are presented.

Glycosidic Bond Expanded Cyclic Oligosaccharides: Synthesis and Host-Guest Binding Property of a Cyclic Pentasaccharide

A new cyclic pentasaccharide comprising an oxymethylene glycosidic bond connecting the individual α-d-glycopyranoside monomers is synthesized through cycloglycosylation of a linear pentasaccharide precursor, which, in turn, is synthesized through the block glycosylation method. Molecular modeling shows that the 30-membered macrocyclic pentasaccharide is a distorted ellipsoid structure, with the lower and upper rims occupied by secondary and primary hydroxyl groups, respectively. Following the synthesis, the microenvironment of the cyclic pentasaccharide is assessed through thermodynamic evaluation upon complexation with 1-aminoadamantane in an aqueous solution, which shows the formation of ∼1:2 host-to-guest complex and a binding affinity of 10 500 (±425) M^-1. Synthesis and assessment of the host-guest binding property of the new glycosidic bond expanded cyclic pentasaccharide are presented.

Efficient Cleavage of Permethylated Cyclodextrins

The cleavage of a permethylated α-cyclodextrin, that is, purity and chemical yield of a maltohexaose derivative thus obtained, was decisively affected by the reaction time. The matrix-assisted laser desorption ionization time-of-flight mass spectrometry spectra with synthetic data enable us to improve the cleavage reaction more efficiently. The optimized conditions developed in the present study allow us to cleave the permethylated γ-cyclodextrin to afford a maltooctaose derivative as a new synthetic building block in a high chemical yield.

Oligoamylose-entwined porphyrin: excited-state induced-fit for chirality induction

An oligoamylose-strapped porphyrin displayed circularly polarized luminescence (CPL) in the S₁ state despite being silent in circular dichroism (CD) in the ground state, suggesting chirality induction in the photoexcited porphyrin moiety from the oligoamylose-strap in the photoexcited state.

Tuning the cavity of cyclodextrins: altered sugar adaptors in protein pores

Cyclodextrins (CDs) have been widely used in host-guest molecular recognition because of their chiral and hydrophobic cavities. For example, β-cyclodextrin (βCD) lodged as a molecular adaptor in protein pores such as α-hemolysin (αHL) is used for stochastic sensing. Here, we have tuned the cavity and overall size of βCD by replacing a single oxygen atom in its ring skeleton by a disulfide unit in two different configurations to both expand our ability to detect analytes and understand the interactions of βCD with protein pores. The three-dimensional structures of the two stereoisomeric CDs have been determined by the combined application of NMR spectroscopy and molecular simulation and show distorted conformations as compared to natural βCD. The interactions of these synthetic βCD analogues with mutant αHL protein pores and guest molecules were studied by single-channel electrical recording. The dissociation rate constants for both disulfide CDs from the mutant pores show ∼1000-fold increase as compared to those of unaltered βCD, but are ∼10-fold lower than the dissociation rate constants for βCD from wild-type αHL. Both of the skeleton-modified CDs show altered selectivity toward guest molecules. Our approach expands the breadth in sensitivity and diversity of sensing with protein pores and suggests structural parameters useful for CD design, particularly in the creation of asymmetric cavities.

Synthesis of Stimuli-Responsive Cyclodextrin Derivatives and Their Inclusion Ability Control by Ring Opening and Closing Reactions

Novel stimuli-responsive cyclodextrins (CDs), in which a disulfide unit was inserted into the rings of permethylated alpha- and beta-CDs, were synthesized. Their inclusion ability was controlled by the opening and closing of the ring based on dithiol-disulfide interconversions.