OPTICAL ENANTIOMORPHS OF (Y ,p-DIAMISOPROPIOSIC ACID

The N-chloroacetyl and N-acetyl derivatives of some thirty racemic amino acids have been employed as starting materials for the subsequent enzymatic separation of the compounds into their opt.ical enantiomorphs (l-3).’ The procedure was always conducted in the absence of added buffer salts, the pH being set at 7 to 8 by addition of alkali to the aqueous solutions of the substrates. At the conclusion of the asymmetric enzymatic hydrolysis, the pH of the mixtures usually decreased by no more than 0.2 pH unit. When, however, a resolution of OL ,fl-dichloroacetyl-m-diaminopropionic acid (1) was recently undertaken with hog kidney acylase I, it was noted that, a rapid decrease in pH of the mixture accompanied the enzymatic digestion. Formation of acid proceeded to such an extent that the enzyme shortly became inactivated (about pH 5). Analysis of the mixture revealed the presence of hydrochloric acid. Solutions of the compound at pH 7.5 in the absence of enzyme showed no change in pH and contained no trace of inorganic chloride. The progressive liberation of hydrochloric acid was evidently due to the presence of the enzyme. When the digest with acylase I was maintained at pH 7.5 for a brief period by the constant addition of alkali, @-chloroacetyl+diaminopropionic acid could be subsequently isolated in pure form and low yield. This compound in aqueous solution maintained at pH 7.5 rapidly liberated hydrochloric acid at the same rate as did cu , p-dichloroacetyl-m-diaminopropionic acid under the same conditions in the presence of the enzyme. The liberation of acid in the digest thus follows as a spontaneous, secondary reaction to the hydrolysis. In view of these observations, a!, p-diacetyl-DL-diaminopropionic acid was employed as starting material for the resolution with acylase I. The products of the enzymatic reaction were P-acetyl-L-diaminopropionic acid, acetic acid, and (Y, p-diacetyl-n-diaminopropionic acid, analogous to the