A molecular receptor selective for zwitterionic alanineElectronic supplementary information (ESI) available: NMR, IR and HMR spectra, X-ray diffraction data and modelling studies. CCDC 1502523-1502525. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ob02237e

A molecular receptor has been synthesized joining an aza-crown ether with a chiral chromane which mimics the oxyanion hole of the enzymes. With this receptor an apolar host-guest complex with zwitterionic alanine has been achieved through the formation of up to seven H-bonds. This complex allows the extraction of aqueous alanine to a chloroform phase, while other natural amino acids are poorly extracted or are not extracted at all. Due to the chiral nature of the receptor, enantioselective extraction from the aqueous alanine solution to a chloroform phase takes place. X-Ray analysis combined with anisotropic effects, NOE and CD studies revealed the absolute configuration of both strong and weak complexes. Modelling studies also support the proposed structures. The presence of an oxyanion-hole motif in this structure was corroborated by X-ray diffraction studies. A new chiral chromane receptor has been synthesized with a right-sized oxyanion hole to fix zwitterionic alanine. This associate allows the enantioselective extraction of this amino acid from water to chloroform.