Homochiral oligomerization of L-histidine in the presence of liposome membranes

We report about a novel method for the homochiral oligomerization of l-amino acids in the presence of liposomes. For this homochiral oligomerization, we took advantage of the superior properties of liposomes as chiral adsorbent, concentrator of reacting molecules, and as effective reaction medium. Indeed, liposomes composed of l-phospholipids could enantioselectively bind and concentrate only l-histidine (l-His) on the liposome membrane, and not D-His, which was confirmed by UV measurements. Furthermore, we demonstrate that the liposomes enabled effective oligomerization of l-His on or in the liposome membrane, while the oligomerization of d-His in the liposome system—or in absence of liposomes—was less efficient. The experimental findings are supported by logP value calculations. These calculations indicate that activated intermediates locate in the center of the bilayer where they are protected from hydrolysis due to the hydrophobic environment of the liposome membrane. Therefore, the use of liposomes from l-phospholipids enables homochiral oligomerization and more efficient oligomerization of l-amino acids as compared to d-amino acids. Thus, our developed method could be used for the synthesis of homochiral polymers from racemic mixtures of monomers and may contribute to the understanding of prebiotic biopolymer formation.