General Method of Diastereo- and Enantioselective Synthesis of β-Hydroxy-α-amino Acids by Condensation of Aldehydes and Ketones with Glycine

Article abstract of DOI:10.1021/ja00300a030

The condensation of formaldehyde with a Ni(II) complex of glicyne Schiff base with (S)-2-acetophenone (1) or (S)-2-benzophenone (2) in CH3OH at 25 deg C in the presence of Et3N yields (S)-Ser with an enantiomeric excess (ee) of 80-90percent.The same reaction gives rise to (R)-Ser with an ee greater than 80percent in the presence of more than 0.2 N CH3ONa, α-(hydroxymethyl) serine being formed in negligible quantities.The reaction of benzaldehyde, 3,4-(methilenedioxy)benzaldehyde, and acetaldehyde with these Gly complexes in 0.2 N CH3ONa at 25 deg C yields β-hydroxy-α-amino acids: (R)-β-phenylserine, (R)-3,4-(methylenedioxy)-β-phenylserine, and (R)-threonine, respectively, with a threo/allo ratio ranging from 10:1 up to over 50:1 and ee more than 80percent.Condensation with acetone yields (R)-β-hydroxyvaline with an enantiomeric purity of 70percent.The enantiomerically pure β-hydroxy-α-amino acids can be obtained from pure diastereomers, isolated by chromatography on silica or Toyopearl HW-60.The initial reagents 1 and 2 were recovered with 60-98percent yield.The stereochemical mechanism of the reaction is discussed.