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 degrees C in order to obtain the binding constants (K) and thermodynamic quantities (Delta H and Delta S) 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)-alpha-phenylethylamine, 3-morpholinopropylamine and n-butylamine are discussed from a thermodynamic point of view.