Sodium folate (100 mg.) is dissolved in water (10 ml.). To this is added 1-ethyl-3-(3 dimethylaminopropyl)carbodiimide hydrochloride (100 mg.), followed by the addition of tyrosine methyl ester hydrochloride (32 mg.) dissolved in water (2 ml.). A yellow gelatinous precipitate forms. The mixture is stirred for four hours at room temperature. The precipitated material is extracted into ethyl acetate and washed successively with 1 N sodium bicarbonate (3×10 ml.) 1 N hydrochloric acid (3×10 ml.) and water (2×10 ml.). The solution is dried over anhydrous magnesium sulfate and the ethyl acetate removed on a rotary evaporator. Trituration of the remaining residues with hexane yields yellow crystalline folic acid tyrosine methyl ester conjugate weighing 56 mg.
