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 KL/KD = 4.1 and KD/KL = 3.9, respectively.
The new chiral macrocyclic hosts would further enrich the host–guest
chemistry.