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]In another embodiment, as shown in Scheme 3, the invention is directed to a method for producing D-allo-isoleucine comprising converting (S)-2-methylbutyraldehyde to a diastereomeric mixture of D-allo-isoleucine hydantoin (5R-[(S)-1-methylpropyl]hydantoin) and L-isoleucine hydantoin (5S-[(S)-1-methylpropyl]hydantoin) under conditions whereby no significant racemization of the chiral center in (S)-2-methylbutyraldehyde occurs, followed by contacting said diastereomeric hydantoin mixture with a D-hydantoinase to stereoselectively hydrolyze any D-allo-isoleucine hydantoin in the mixture to the corresponding N-carbamoyl-D-allo-isoleucine. Preferably in the claimed method the contacting of the diastereomeric hydantoin mixture with a D-hydantoinase is carried out under conditions permitting the simultaneous epimerization of the chiral center at C-5 of the hydantoin. As discussed further below, 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-allo-isoleucine in high yield. The N-carbamoyl-D-allo-isoleucine is then decarbamoylated to produce D-allo-isoleucine.
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