An Ultimate Stereocontrol in Supramolecular Photochirogenesis: Photocyclodimerization of 2-Anthracenecarboxylate Mediated by Sulfur-Linked β-Cyclodextrin Dimers

Abstract

Stereoisomeric β-cyclodextrin (CD) dimers linked with a sulfur atom or an arene spacer were designed to create a tethered dual CD capsule for precisely manipulating the regioand enantioselectivities of the photocyclodimerization of 2anthracenecarboxylate (AC) to four stereoisomeric classical 9,10:9′,10′-cyclodimers and two nonclassical 5,8:9′,10′-cyclodimers. Among the dimeric CD hosts prepared, exo-3-thia-β-CD dimer formed 1:1 and 1:2 host−guest complexes with AC in aqueous solutions, the former of which hindered but the latter facilitated the AC photocyclodimerization with regio-and enantioselectivities much higher than those obtained with native β-CD or the rest of the β-CD dimers. The stereochemical outcomes turned out to be highly sensitive to and hence critically manipulable by the linking position and configuration of the connected saccharide units and the linker length, as well as the external variants, such as temperature, pH, and added salt. Eventually, the photocyclodimerization of AC mediated by the dimeric β-CD host gave enantiopure syn-head-to-tail-9,10:9′,10′-cyclodimer in 97−98% yield in a pH 5.1 buffer solution at 0.5 °C and also in an aqueous CsCl solution at −20 °C.

Enantiodifferentiating Photodimerization of a 2,6‐Disubstituted Anthracene Assisted by Supramolecular Double‐Helix Formation with Chiral Amines

“…By comparison with the experimental results (22:78 and +30 % ee (( P )‐ anti ‐ 2 rich) at 25 °C and 57:43 and −98 % ee (( M )‐ anti ‐ 2 rich) at −35 °C, respectively; runs 6 and 9 in Table ), the calculated anti / syn ratio and highly ( M )‐ anti ‐ 2 enantioselectivity at −35 °C were in roughly agreement with the observed ones, but those at 25 °C disagree with the experimental results. Hence, as in the case for the photodimerization of 1 , we may conclude that the enantioselectivity of the chiral anti ‐ 2 photodimer as well as the diastereoselectivity of the anti ‐ 2 and syn ‐ 3 mostly result from the difference in the excited‐state reactivities of the diastereomeric right‐ and left‐handed double‐helical inclusion complexes (( 1 ) 2 ⋅(( R )‐ 4 ) 4 ) rather than the difference in their ground‐state stabilities . However, the reasons for poor anti ‐ 2 / syn ‐ 3 selectivity and highly temperature‐dependent enantioselectivity of anti ‐ 2 with accompanying inversion of the product chirality at 25 °C during the photodimerization of 1 in the presence of chiral amines remain unclear, which may not be completely explained by the difference in the excited‐state reactivities based on the calculation results of the ground‐state stabilities.…”

Prebiotics‐Encapsulated Probiotic Spores Regulate Gut Microbiota and Suppress Colon Cancer

“…Through the host–guest interaction mediated by β‐cyclodextrin (β‐CD) and adamantine (AD), the prebiotic dextran was coated outside the spores of C. butyricum , as shown in Figure a. [ 26,27 ] In the anaerobic environment of the gut, the dextran‐encapsulated spores (spores‐dex) will revive, decompose dextran, and enrich in the tumor tissues specifically. The introduction of dextran improves the intestinal adhesion, [ 28 ] promotes the fermentation of C. butyricum and then produces a large amount of anti‐cancer SCFA.…”

Polysaccharide- and β-Cyclodextrin-Based Chiral Selectors for Enantiomer Resolution: Recent Developments and Applications

“…Tethering β-cyclodextrin derivatives to the support matrix, to enhance chiral recognition ability, is a new approach in β-cyclodextrin-based CSs [ 68 , 69 , 70 ]. A more detailed insight into the mechanism of enantiodifferentiation with cyclodextrins is referred to in Ji et al [ 71 ], Wei et al [ 72 ], and Dai and Wu et al [ 73 ].…”