Cyclophane receptor, chiral

A novel sterically congested cliv-like receptor for dicationic quests, incorporating a hindered cyclophane possessing chiral spirobiindanol phosphonate and phosphate units (32) has been synthesised P-Nitrosophosphates (33) have been obtained and used as new N-O hetero-dienophiles in the Diels-Alder type reaction with a few selected 1,3-dienes to give highly functionalized cycloadducts (34). The latter can be directly transformed by... 

Fig. 5 Typical cyclophane receptors for metal ion complexation (siderophore 31. torand 32, crown ether 36), onium ion-rt interactions (33, crpptophane 38). hydrogen bonding interactions (34-37), and chiral recognition (36-38). Self-assembled cyclophanes 39 and 40.

The cage-type cyclophane furnishes a hydrophobic internal cavity for inclusion of guest molecules and exercises marked chiral discrimination in aqueous media. The host embedded in the bilayer membrane is capable of performing effective molecular recognition as an artificial cell-surface receptor to an extent comparable to that demonstarated by the host alone in aqueous media. 

The spherically shaped cryptophanes are of much interest in particular for their ability to bind derivatives of methane, achieving for instance chiral discrimination of CHFClBr they allow the study of recognition between neutral receptors and substrates, namely the effect of molecular shape and volume complementarity on selectivity [4.39]. The efficient protection of included molecules by the carcerands [4.40] makes possible the generation of highly reactive species such as cyclobutadiene [4.41a] or orthoquinones [4.41b] inside the cavity. Numerous container molecules [A.38] capable of including a variety of guests have been described. A few representative examples of these various types of compounds are shown in structures 59 (cyclophane) 60 (cubic azacyclophane [4.34]), 61a, 61b ([4]- and [6]-calixa-renes), 62 (cavitand), 63 (cryptophane), 64 (carcerand). 

Wilcox, C S, Cowart, M D, New approaches to synthetic receptors. Studies on the synthesis and properties of macrocyclic C-glycosyl compounds as chiral, water-soluhle cyclophanes, Carbohydr. Res., 171, 141-159, 1987. 

Bukownik, R. R., Wilcox, C. S. Synthetic receptors. 3,6-anhydro-7-benzenesulfonamido-1,7-dideoxy-4,5-0-isopropylidene-D-altro-hept-1-ynitol a useful component for the preparation of chiral water-soluble cyclophanes based on carbohydrate precursors. J. Org. Chem. 1988, 53, 463 67. 

Diederich and coworker have synthesized chiral receptors that possess additional carboxylate residues that are suitable for the complexation of disaccharides [54]. Cyclophanes 141-143 were prepared via a stepwise approach involving chain elongation steps followed by a single intramolecular cyclization reaction. The complexation of these receptors with two disaccharides was investigated by H NMR spectroscopy and showed that the incorporation of the methyl carboxylate groups in 142 increased the assodation relative to the unfunctionalized derivative 141. A subsequent publication reported on the detailed binding affinities of square cydo-... 

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