Synthesis of 4-sulfur-substituted (2S,3R)-3-phenylserines by enzymatic resolution. Enantionure precursors for thiamphenicol and florfenicol

Article abstract of DOI:10.1021/op970045t

Enantiomerically pure 4-methylthio- and 4-methylsulfonylsubstitutcd (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 (25,3R)-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,3A)-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.