Coupling with Active Esters

Abstract

l-Tyrosine ethyl ester [2] (2.30 g, 11 mmol) is dissolved, with gentle warming, in dry tetrahydrofurane (5 ml). The solution is cooled to room temperature and N-benzyloxycarbonyl-S-benzyl-l-cysteine cyan methyl ester [1, 3] (3.84 g, 10 mmol) is added followed by a catalytic amount (0.03 ml) of acetic acid. The reaction is allowed to proceed at room temperature for two days. The solvent is removed in vacuo, the residue dissolved in ethyl acetate (100 ml) and the solution extracted with 0.5 N KHCO₃ (50 ml), water (50 ml), 0.5 N HC1 (50 ml) and water (50 ml), dried over anhydrous Na₂SO₄ and evaporated to dryness in vacuo.