Application of pH-responsive methylpropargyl leucine polymer in enantioselective crystallization

In this study, novel 1-methylpropargyl alcohol derivatives containing leucine side groups on their side chains were successfully synthesized and polymerized using (nbd)Rh+[η6-C6H5B−(C6H5)3] as catalyst. Circular dichroism (CD) and ultraviolet-visible (UV-Vis) spectra revealed that the polymers took predominantly one-handed helical structures that were stable under heat. Deprotection of the t-butyloxycarboryl (Boc) groups in the homopolymers under acidic conditions produced polymers with primary amine moieties on the side chains. The polymers were soluble in aqueous medium, and turbidity test revealed that they were pH-responsive. Amino acid-based polymers were further used in the enantionselective crystallization of alanine enantiomers and l-alanine was preferably induced to crystallize with the l-leucine-based polymer.