A suspension of 2.3 g (1R,2R)-2-(3,3-Difluoro-azetidine-1-carbonyl)-4-oxo-cyclopentanecarboxylic acid ethyl ester in 50.6 mL aqueous buffer (30 mM 2-(N-morpholino)ethanesulfonic acid; 0.5 M D-glucose [2.7 equ.]; 2 mM Magnesium chloride) was adjusted to pH 6.5 at 35° C. Under stirring the reduction was started by the addition of the cofactor NADP (23 mg [0.03 equ.]), the cofactor regeneration enzyme-glucose dehydrogenase (23 mg GDH 102 [Codexis]) and the reductase (23 mg KRED-NADP-131 [Codexis]). During the 17 h reaction time at 35° C. the pH was kept at pH 6.5 by the addition of 8.25 mL 1M NaOH. Under stirring the mixture was mixed with 1.5 g filter aid—Dicalite—and 30 mL ethyl acetate for at least 10 min. at room temperature. Subsequently the filter aid was washed with 30 ml water and 70 mL ethyl acetate. Afterwards the filter aid was discarded. The filtrate was extracted trice with 100 mL ethyl acetate. Treatment of the combined organic phases with sodium sulfate, evaporation and drying over night on a high vacuum yielded in 2.21 g of the title compound. MS: 278.2 (M+H)+; chiral GC: ee 99.5% [BGB-172, 60 m; H2; 10° C./min, 100° C. to 180° C.; 1° C./min, 180° C. to 230° C.].
