2-Chloropropionate resolution

The resolution of racemic ethyl 2-chloropropionate with aliphatic and aromatic amines using Candida cylindracea lipase (CCL) [28] was one of the first examples that showed the possibilities of this kind of processes for the resolution of racemic esters or the preparation of chiral amides in benign conditions. Normally, in these enzymatic aminolysis reactions the enzyme is selective toward the (S)-isomer of the ester. Recently, the resolution ofthis ester has been carried out through a dynamic kinetic resolution (DKR) via aminolysis catalyzed by encapsulated CCL in the presence of triphenylphosphonium chloride immobilized on Merrifield resin (Scheme 7.13). This process has allowed the preparation of (S)-amides with high isolated yields and good enantiomeric excesses [29]. 

Ue 7.13 Dynamic kinetic resolution of 2-Chloropropionate by enzymatic aminolysis. 

Another chiral small molecule, (S)-2-chloropropionic acid (S-CPA), is a key intermediate in the synthesis of the 2-phe-noxypropionic acid class of herbicides, including Fusilade (Avecia) and Mecoprop (BASF). Kinetic resolution of racemic CPA is performed with a whole cell biocatalyst expressing a dehalogenase enzyme selective for the (R)-enantiomer and producing (S)-lactic acid, itself a useful byproduct. The (S)-chloropropionic acid is extracted with a... 

Enzymes are often used in kinetic resolutions, when one isomer reacts much faster than the other.25 This can be done on an industrial scale. Zeneca uses a dehalogenase on racemic 2-chloropropionic acid to obtain about 2000 ton/yr of the L-isomer for use in making a herbicide.26 Enzymatic resolutions may involve ring opening of epoxides,27 formation or hydrolysis of esters and amides, reduction of carbonyl compounds, and so on. Lipases are often used for this purpose.28 A typical example is reaction 10.16.29... 

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