Microbial generation of (2R,3S)- and (2S,3S)-ethyl 2-benzamidomethyl-3-hydroxybutyrate, a key intermediate in the synthesis of (3S,1′R)-3-(1′-hydroxyethyl)azetidin-2-one

Microbial reduction of the carbonyl group of the substituted acetoacetate esters 3–6 affords directly, or after Ni-Raney desulfurization, the corresponding enantiomerically pure 3S carbinols of variable diastereoisomeric composition. These compounds are transformed into (3S,1′R)-3-(1′-hydroxyethyl)-azetidin-2-one, a useful intermediate in the synthesis of β-lactam antibiotics.