Aldehyde reductase (ALR, E.C.I. 1.1.2) from Sporobolomyces salmonicolor can reduce ethyl 4-chloro-3-oxobutanoate (COBE) to (R)-CHBE.

• coli M15(pQE30-alr0307) 。 用重组菌作为催化剂；解决了用常规酵母细胞转化COBE；产物是部分外消旋的R；S-(+)-4-氯-3羟基丁酸乙酯；e.