Chiral Schiff base derivatives of calix[4]arene: synthesis and complexation studies with chiral and achiral amines

Novel chiral Schiff base derivatives of calix[4]arenes 1–3 have been prepared from the reaction of 5,17-diformyl-25,27-dipropoxy-26,28-dihydroxycalix[4]arene 4 with (S)-(−)-1-phenylethylamine, (R)-(−)-1-cyclohexylethylamine, and (R)-(−)-2-heptylamine, respectively, by a convenient method in 69–80% yields. Spectrophotometric titrations have been performed in CHCl3 at 20–30 °C in order to obtain the binding constants (K) and thermodynamic quantities (ΔH and ΔS) for the stoichiometric 1:1 inclusion complexation of various amines with these new host compounds. The molecular recognition abilities and enantioselectivity for guests (R)- and (S)-α-phenylethylamine, 3-morpholinopropylamine and n-butylamine are discussed from a thermodynamic point of view.

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(5S,17S)-Di(phenylethylimido)-25,27-dipropoxy-26,28-dihydroxycalix[4]areneC52H54O4N2[α]D20=+54.7 (c 0.5 CHCl3)Source of chirality: (S)-(−)-1-phenylethylamineAbsolute configuration: (S,S)

(5R,17R)-Di(cyclohexylethylimido)-25,27-dipropoxy-26,28-dihydroxycalix[4]areneC52H66O4N2[α]D20=-4.5 (c 0.4 CHCl3)Source of chirality: (R)-(−)-1-cyclohexylethylamineAbsolute configuration: (R,R)

(5R,17R)-Di(2-heptylimido)-25,27-dipropoxy-26,28-dihydroxycalix[4]areneC50H66O4N2[α]D20=-2.1 (c 0.4 CHCl3)Source of chirality: (R)-(−)-2-heptylamineAbsolute configuration: (R,R)