A mixture of 3-hydroxy-alpha-methyl-L-tyronsine (I), alpha-chloroethylpivalate (II) and tetramethylurea (III) is heated at 70-5 C to yield the pivaloyloxyethyl ester hydrochloride (IV). The reaction mixture is diluted with methyl isobutyl ketone and filtered. The filtrate is washed sequentially with saturated NaHCO3 and NaCl solution. Crystallization of 3-hydroxy-a-methyl-L-tyrosine 1-(2,2-dimethyl-1-oxopropoxy)ethyl ester (V) is induced by seeding the solution of (V) in methyl isobutyl ketone. The phosphate or tartrate of (V) may be obtained by adding dilute aqueous e phosphoric acid or tartaric acid to an ethyl acetate: solution of (V).

A mixture of 3-hydroxy-alpha-methyl-L-tyronsine (I), alpha-chloroethylpivalate (II) and tetramethylurea (III) is heated at 70-5 C to yield the pivaloyloxyethyl ester hydrochloride (IV). The reaction mixture is diluted with methyl isobutyl ketone and filtered. The filtrate is washed sequentially with saturated NaHCO3 and NaCl solution. Crystallization of 3-hydroxy-a-methyl-L-tyrosine 1-(2,2-dimethyl-1-oxopropoxy)ethyl ester (V) is induced by seeding the solution of (V) in methyl isobutyl ketone. The phosphate or tartrate of (V) may be obtained by adding dilute aqueous e phosphoric acid or tartaric acid to an ethyl acetate: solution of (V).