Efficient synthesis of chiral binaphthol aldehyde with phenyl ether linkage for enantioselective extraction of amino acids

A binaphthol aldehyde with phenyl ether linkage, compound 2, has been synthesized starting from binaphthol-3-carboxylic acid. The axially chiral binaphthol ring was racemized during the synthesis due to high temperatures required in O-phenylation reaction. The enantiomerically pure form of 2 was obtained from the resolution of the diastereomeric imine of 2. Optically pure compound (S)-2 was applied to the enantioselective liquid-liquid extraction of amino acid between CH₂Cl₂ and aqueous layers.The stereoselectivities, that is, D/L ratio of the amino acid extracted, ranged from 3.57 to 11.1. One carbon was absent in compound (S)-2 compared to the compound (S)-1 with benzyl ether linkage, which differentiated the conformations of their imines formed with amino acids.