Guanidinium Receptors as Enantioselective Amino Acid Membrane Carriers

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• 作者：Perla Breccia ; Michiel Van Gool ; Ruth Pé ; rez-Ferná ; ndez ; Sonsoles Martí ; n-Santamarí ; a ; Federico Gago ; Pilar Prados ; and Javier de Mendoza
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：July 9, 2003
• 年：2003
• 卷：125
• 期：27
• 页码：8270 - 8284
• 全文大小：284K
• 年卷期：v.125,no.27(July 9, 2003)
• ISSN：1520-5126

文摘

A number of artificial carriers for the transport of zwitterionic aromatic amino acids across bulkmodel membranes (U-tube type) have been prepared and evaluated. 1,2-Dichloroethane and dichloromethane were employed in the organic phase. All compounds are based on a bicyclic chiral guanidiniumscaffold that ideally complements the carboxylate function. The guanidinium central moiety was attachedto crown ethers or lasalocid A as specific subunits for ammonium recognition as well as to aromatic orhydrophobic residues to evaluate their potential interaction with the side chains of the guest amino acids.The subunits were linked to the guanidinium through ester or amide connectors. Amides were found to bebetter carriers than esters, though less enantioselective. On the other hand, crown ethers were superior tolasalocid derivatives. As expected, transport rates were dependent on the carrier concentration in the liquidmembrane. Reciprocally, enantioselectivities were much higher at lower carrier concentrations. The resultsshow that our previously proposed three-point binding model (J. Am. Chem. Soc. 1992, 114, 1511-1512),involving the participation of the aromatic or hydrophobic residue to interact with the side chains of theamino acid guest, is unnecessary to explain the high enantioselectivities observed. Molecular dynamicsfully support a two-point model involving only the guanidinium and crown ether moieties. These moleculesconstitute the first examples of chiral selectors for underivatized amino acids acting as carriers under neutralconditions.