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Tetrasulfonate derivatives of calix[4]resorcarene (calix[4]arene derived from resorcinol) (1) form 1 : 1 complexes with highly hydrophilic guest molecules, such as ethers, alcohols, ketones, and sulfoxides, in water. The affinities of three types of the guests increase in the order CH3–X–CH3 < (–CH2CH2–X–)2 < CH3–X–CH2CH2–X–CH3 (X = O, CH(OH), C=O, or S=O), reflecting the importance of multiple host-guest interactions. The binding constants (K) with respect to X increase in the order O < CH(OH) < C=O < S=O or CH(OH) < O < C=O < S=O. As for the effects of substituents Y on 2-C of the benzene rings of the host, both 1b (Y = CH3) and 1c (Y = OH) exhibit higher binding capabilities than does the parent host 1a (Y = H). Thus, the present complexation is promoted by electron-withdrawing residue (X) in the guests and electron-donating substituents (Y) in the host. The binding of CH3–X–CH3 (X = C=O or S=O) to hosts 1a—c is characterized by favorable enthalpy changes and unfavorable entropy changes. These results, coupled with NMR data, indicate that the driving force of the present complexation is a C–H···π interaction between C–H bonds of a guest as soft acids and benzene rings of the host as soft bases.

Aldoses were epimerized at C-2 by Ca2+ in aqueous or alcoholic basic solutions through a stereospecific [1-2] rearrangement of the carbon skeletons of the aldose. The skeletal rearrangement was confirmed by 13C NMR analysis of the reaction products. The reaction of [1-13C]- and [2-13C]-d-glucose afforded [2-13C]- and [1-13C]-d-mannose, respectively, as major products. The effects of metal ions, bases, and solvents were examined, and it was found that a high concentration of Ca2+ and a base (>pH 12.3) were especially effective for the present rearrangement. Separation of the reaction products was also effected by using Ca2+ cation-exchange chromatography. Thus, under the optimized conditions, d-mannose and d-lyxose, which are rare in nature and expensive, were easily obtained in high isolated yields from d-glucose and d-xylose, respectively.

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