O-methyl-L-tyrosine N-Methylamide → 6-Methyl-4-[[[1-[(methylamino)carbonyl]-2-(4-methoxyphenyl)ethyl]amino]carbonyl]hept-3-enoic acid, methyl ester

N,N-Dicyclohexylcarbodiimide (515 mg, 2.5 mmol) was added to an ice-cooled solution of 4-methoxycarbonyl-2-(2-methylpropyl)but-2-enoic acid (500 mg, 2.5 mmol) and O-methyl-L-tyrosine N-methylamide (520 mg, 2.5 mmol) in dry dichloromethane (30 ml), and the mixture was stirred at room temperature for 18 h. The precipitated solid was filtered off and washed with a little dichloromethane, then the organic solution was washed successively with 1N hydrochloric acid (20 ml), 1N sodium bicarbonate (20 ml), and water. The solution was dried (MgSO4) and evaporated in vacuo. Column chromatography (30 g silica) of the residual solid, eluting with 5% methanol/dichloromethane gave the title compound (520 mg, 53%), m.p. 142°-144° C. (dichloromethane/pentane).