Enzymatic Resolution of DL-Alanine

Prelab Exercise Discuss at least three other methods for resolving OL-alanine into its enantiomers. Judging from its name, would you expect acylase to be equally effective on the acetyl derivatives of other amino acids Explain why the enzyme acylase will hydrolyze only one of a pair of enantiomers and how a mixture of l-alanine and N-acetyl-o-alanine can be separated at the end of the reaction. 

Resolution of DL-alanine (1) is accomplished by heating the N-acetyl derivative (2) in weakly alkaline solution with acylase, a proteinoid preparation from porcine kidney containing an enzyme that promotes rapid hydrolysis of N-acyl derivatives of natural L-amino acids but acts only immeasurably slowly on the unnatural o-isomers. N-Acetyl-DL-alanine (2) can thus be converted into a mixture of l-( + )-alanine (3) and N-acetyl-o-alanine (4). The mixture is easily separable into the components, because the free amino acid (3) is insoluble in ethanol and the N-acetyl derivative (4) is readily soluble in this solvent. Note that, in contrast to the weakly levorotatory o-( - )-alanine (a 14.4°), its acetyl derivative is strongly dextrorotatory. 

The acetylation of an a-amino acid presents the difficulty that, if the conditions are too drastic, the N-acetyl derivative (4) is converted in part 

1 Drying N-acetyl-ou-alanine under reduced pressure. 

The azlactone of oL-alanine is known only as a partially purified liquid. 

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