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.