Optically active hexaazamacrocycles: Protonation behavior and chiral-anionrecognition

The protonation features of two optically active 22-membered hexaazamacrocy cles possessing one (L1) or two (L2) (R,R)-cyclohexane-1,2-diamine moieties have been studied by means of potentiometric H-1- and C-13-NMR techniques. This study allows the determination of the basicity constants and the step wise protonation sites. The presence of the cyclohexane decreases the proto nation ability, and this effect can be explained in terms of conformational and electrostatic factors Binding of different chiral dicarboxylates has b een studied by potentiometry. Macrocycle L2 presents higher anion-complexat ion equilibrium constants than L1. The stability of the diastereoisomeric c omplexes depends on the pH. and the structures of the macrocycles and anion s Receptor L1.6H(+) shows moderate D-selectivity towards tartrate anion. wh ereas L2.6H(+) exhibits a good preference for N-Ac-D-aspartate. Both proton ated L1 and L2 form strong complexes with N-Ac-glutamate, and the stoichiom etry of the complex depends on the degree of protonation and the absolute c onfiguration of the anion. For this last anion, both azamacrocycles exhibit a clear D-preference.