A New Generation of "Cholaphanes": Steroid-Derived Macrocyclic Hosts with Enhanced Solubility and Controlled Flexibility.

The macrocyclic "cholaphanes" 3a-c were synthesized from the inexpensive steroid cholic acid. Like earlier relatives they feature substantial cavities with inward-directed hydroxyl groups, suitable for binding polar molecules such as carbohydrates in nonpolar media. New features are the externally directed alkyl chains, promoting solubility in organic solvents, and (in the case of 3b/c) reduced conformational freedom resulting from truncation of the steroidal side-chain.

A Molecular Chameleon: Chromophoric Sensing by a Self-Complexing Molecular Assembly.

A color change from purple to green takes place on addition of tetrathiafulvalene (TTF) to the macrobicyclic receptor 1 , which is composed of a cyclobis(paraquat-p-phenylene) tetracation that shares one of its paraphenylene rings with a 1,5-naphthoparaphenylene-[36]crown-10 macrocycle. The TTF molecule forces the macrobicycle to turn inside out (see schematic drawing below) and displaces the self-complexed 1,5-dioxynaphthalene ring system from the center of the tetracationic cyclophane.

The Complexing Properties of 1-Aminosquarate Derivatives with Lead.

Reaction of three different 1-(dialkylamino) derivatives of 3,4-dihydroxycyclobut-3-ene-1,2-dione (squaric acid) with lead(II) nitrate in aqueous solution yielded polymeric complexes which have been characterized by single-crystal X-ray analysis. Pb[(CH(3))(2)NC(4)O(3)](2)(OH(2))(2).H(2)O (1) produced from 1-(dimethylamino)-2-methoxycyclobutenedione crystallizes in the triclinic space group P&onemacr;, with a = 8.

Synthetic Cyclic Oligosaccharides-Syntheses and Structural Properties of a Cyclo[(1 → 4)-α-L-rhamnopyranosyl-(1 → 4)-α-D-mannopyranosyl]trioside and -tetraoside.

An efficient polycondensation-cyclization approach to the synthesis of cyclodextrin analogues is demonstrated by the preparation of cyclohexaoside 1 and cyclooctaoside 2. The key intermediate, disaccharide 3, bearing the cyanoethylidene group as a glycosyl donor function and the trityloxy group as a glycosyl acceptor function was prepared in 15 steps starting from L-rhamnose and D-mannose. The crucial cyclooligomerization of the disaccharide monomer 3 was carried out in the presence of TrClO as a promoter with the use of ultra-dry conditions at normal concentrations.