Asymmetric Synthesis of α-Amino-β-hydroxy Acids Using a Chiral Pyridoxal-Like Pyridinophane–Zinc Complex as an Enzyme Mimic; Scope and Limitation

Abstract A chelate complex (4) with high homogeneity was precipitated upon stirring a mixture of zinc(II) ion and a Schiff base produced from glycine and (R)- or (S)-15-formyl-14-hydroxy-2,8-dithia[9](2,5)pyridinophane, chiral pyridoxal-like pyridinophane. A four-coordinated zinc chelate complex was newly proposed as the structure of 4. Aldol condensations between 4 and several aldehydes were attempted at pH 10.0. Only small linear chain aldehydes, such as acetaldehyde and propionaldehyde, could react with 4 under these conditions to give the corresponding α-amino-β-hydroxy acid in the range of 27–77% enantiomeric excess.