Prochiral dicarboxylic acid esters

Table 11.1-7. a-Chymostrypsin-catalyzed enantiotopos-differentiating hydrolysis of prochiral cyclic dicarboxylic acid esters, acyclic dicarboxylic acid esters and cyclic diol diacetates and enantiomer-differentiating hydrolysis of racemic carboxylic acid esters in aqueous solution. 

In kinetic resolutions (Scheme 3.2-3.5) it is often the case that one of the products is required, while the other is not and must be discarded or recycled (e.g. racemised). Such operations can be wasteful or expensive. On the other hand, the biotransformation of wcso-compounds or prochiral compounds allows for the possibility of preparing an optically pure compound in quantitative yield. In Scheme 3.7, two examples of the use of meso-compounds are described. The diester (11) is made up of a complex dicarboxylic acid unit derivatised as the dimethyl ester. Pig liver esterase catalyses the hydrolysis of one of the ester groups to give the acid (12) (95% e.e.) in 96% yield. This compound is an excellent precursor of the natural product neplanocin. Note that the acid (12) is not a substrate for pie, and thus the reaction stops at the half-way stage. The compound (13), like (11), possesses a plane of symmetry. Hydrolysis catalysed by porcine pancreatic lipase (ppl) affords the alcohol (14) (>98% e.e.) in quantitative yield. The latter compound has been used to make fluorocarbocyclic adenosine (C -adenosine), a stable analogue of the naturally occurring nucleoside adenosine. 

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