Preparation
Preparation of N-Pivaloyl-L-tyrosine Ethyl Ester
N-Pivaloyl-L-tyrosine could not be prepared from L-tyrosine following the previous method. Under the same conditions used for the preparation of IK, 90% of the starting material remained unreacted. N-Pivaloyl-L-tyrosine Ethyl Ester was, however, made from Ie by mild hydrolysis with dilute sodium hydroxide solution and subsequent esterification with absolute ethyl alcohol saturated with dry HCl gas. The material after chromatography on florisil was obtained as an oil. Comparison of the mobility with Ie on thin-layer chromatography in two solvent systems (I and 11) as well as conversion to Ie by further acylation confirmed the identity of the material.
