Enantiomeric Recognition of Amino Acid Salts by Macrocyclic Crown Ethers Derived from Enantiomerically Pure 1,8,9,16-Tetrahydroxytetraphenylenes

Asymmetric synthesis of (R,R)- and (S,S)-1,8,9,16-tetrahydroxytetraphenylenes was achieved from starting material (2R,3R)-butane-2,3-diol and (2S,3S)-butane-2,3-diol respectively by utilizing a center-to-axis strategy. A series of crown ether compounds 20, 24, and 25 and their,corresponding enantiomers derived from chiral tetrahydroxytetraphenylene were synthesized in enantiomerically pure forms. Enantiomeric recognition properties of these hosts toward L- and D-amino acid methyl ester hydrochloride were studied by the UV spectroscopy titration. The tetramer hosts (S,S,S,S,S,S,S,S)-20 and (R,R,R,R,R,R,R,R)-20 exhibited the best enantioselectivities toward L- and D-alanine methyl ester hydrochloride salt with K-L/K-D = 4.1 and K-D/K-L = 3.9, respectively. The new chiral macrocyclic hosts would further enrich the host guest chemistry.