Of 125 microorganisms that were able to use a-hydroxy acid amides as sole nitrogen source, Ochrobactrum anthropi NCIMB 40321 was selected for its ability to hydrolyse racemic amides L-selectively. The substrate specificity of whole O. anthropi ceils is remarkably wide and ranges from a-H-a-amino-, a-alkyla-amino, N-hydroxy-a-amino acid amides to a-hydroxy-acid amides. After 50°70 conversion, both the Lacids formed and the remaining D-amides were present in >99°70 enantiomeric excess, and ammonia accumulated in stoichiometric amounts. Using mandelic acid amide as a model substrate, the hydrolysis was optimized. Optimal rates were observed at p H 8.5 at 50 ° C. At higher temperatures the initial rate was even higher; however, fairly rapid inactivation occurred.

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Enantiomerically pure 4-methylthio- and 4-methylsulfonyl-substituted (2S,3R)-3-phenylserines are prepared by enzymatic resolution of the corresponding racemic threo amides using the amidase from Ochrobactrum anthropi NCIMB 40321. The unwanted (2R,3S) enantiomers of the amides are separated from the enantiopure amino acids and easily racemized after Schiff base formation with the corresponding 4-(methylthio)- and 4-(methylsulfonyl)benzaldehyde. The racemization can be combined with the preparation of the racemic amides by aldol reaction under crystallization conditions to yield only the threo isomers. Enantiopure (2S,3R)-3-[4-(methylthio)phenyl]serine and (2S,3R)-3-[4-(methylsulfonyl)phenyl]serine are thus obtained in 78% and 62% overall yields starting from the corresponding substituted benzaldehydes. (2S,3R)-3-[4-(Methylthio)phenyl]serine is reduced to (1R,2R)-2-amino-1-[4-(methylthio)phenyl]propane-1,3-diol with NaBH4/H2SO4 and can be used for the synthesis of thiamphenicol and florfenicol.

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