Enantiomeric recognition of amino acid derivatives by chiral schiff bases of calix[4]arene

Novel calix[4]arene Schiff bases bearing chiral substituents both on the upper and the lower rims have been developed. These chiral receptors exhibit good chiral recognition ability towards α-amino acid ester hydrochlorides (up to KD/KL = 4.36, ΔΔG0 = − 3.65 kJ mol−1) in CHCl3. The molecular recognition abilities and enantioselectivities for guests are also discussed from a thermodynamic point of view.

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(40R,50R)-(5S,17S)-Di(phenylethylimido)-25,27-dihydroxy-26,28-(40,50-di-1-methylethoxy-carbonyl-30,60-dioxa-20,70-dioxooctylene)-dioxycalix[4]areneC60H60O12N2[α]D20=+14.1 (c 0.4 CHCl3)Source of chirality: (S)-(−)-1-phenylethylamine, l-(+)-tartaric acid diisopropyl esterAbsolute configuration: (S,S,R,R)

(40R,50R)-(5R,17R)-Di(cyclohexylethylimido)-25,27-dihydroxy-26,28-(40,50-di-1-methylethoxy-carbonyl-30,60-dioxa-20,70-dioxooctylene)-dioxycalix[4]areneC60H72O12N2[α]D20=-5.0 (c 0.4 CHCl3)Source of chirality: (R)-(−)-1-cyclohexylethylamine, l-(+)-tartaric acid diisopropyl esterAbsolute configuration: (R,R,R,R)

(40R,50R)-(5R,17R)-Di(2-heptylimido)-25,27-dihydroxy-26,28-(40,50-di-1-methylethoxy-carbonyl-30,60-dioxa-20,70-dioxooctylene)-dioxycalix[4]areneC58H72O12N2[α]D20=-30.6 (c 0.4 CHCl3)Source of chirality: (R)-(−)-2-heptylamine, l-(+)-tartaric acid diisopropyl esterAbsolute configuration: (R,R,R,R)