N1CC(=O)NC1=O.[NH2:8][C@@H:9]([C:14]([OH:16])=[O:15])[C@@H:10]([CH2:12][CH3:13])[CH3:11].N1CC(=O)NC1=O.N[C@H](C(O)=O)[C@@H](CC)C.N1CC(=O)NC1=O.C(N[C@@H](C(O)=O)[C@@H](CC)C)(=O)N>C[C@H](CC)C=O>[NH2:8][C@@H:9]([C:14]([OH:16])=[O:15])[C@@H:10]([CH2:12][CH3:13])[CH3:11]Methods for producing single diastereomers of isoleucine in high stereochemical purity are provided. D-isoleucine is produced by converting (R)-2-methylbutyraldehyde to a diastereomeric mixture of D-isoleucine hydantoin and L-allo-isoleucine hydantoin (5S-[(R)-1-methylpropyl]hydantoin) under conditions whereby no significant racemization of the chiral center in (R)-2-methylbutyraldehyde occurs, followed by contacting said diastereomeric hydantoin mixture with a D-hydantoinase to stereoselectively hydrolyze any D-isoleucine hydantoin in the mixture to the corresponding N-carbamoyl-D-isoleucine, preferably under conditions permitting the simultaneous epimerization of the chiral center at C-5 of the hydantoin. The simultaneous epimerization permits the reaction to be carried out to substantial completion so that the diastereomeric hydantoin mixture is converted to N-carbamoyl-D-isoleucine in high yield. The N-carbamoyl-D-isoleucine is then decarbamoylated to produce D-isoleucine. Similar procedures are used to produce single diastereomers of L-isoleucine, L-allo-isoleucine, and D-allo-isoleucine.
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