The availability of leucine derivatives for growth of rats

A number of synthetic derivatives of the essential amino acid leucine were tested for biological activity using the growth of rats as the main criterion. Of these, glycyl- l -leucine, acetyl- l -leucine, l -leucine ethyl ester, and l -leucine methyl ester supported growth while caproic acid, phthaloyl- l -leucine, benzoyl- dl -leucine, and carbobenzoxy- l -leucine were found to be inactive. Chloroacetyl- l -leucine actually suppressed growth to a greater degree than a leucine-deficient diet. The N-methyl derivative of leucine was only slightly active. Comparison of the N-acetyl derivatives of l - and dl -leucines indicates that N-acetyl- d -leucine is devoid of any activity.