At 0° C. to a solution of 165 mg of a mixture of the (E)- and (Z)-isomers of 1-(4-phenyl-but-1-enyl)-naphthalene-2-carboxylic acid in 2 ml abs. DMF under inert atmosphere 95 mg 1-hydroxybenzotriazole, 110 μl N,N′-diiospropylcarbodiimide and 98 μl N,N-diisopropylethylamine were added. After 15 min at 0° C. 86 mg amino-isobutyric acid methyl ester hydrochloride and 98 μl N,N-diisopropylethylamine were added and the reaction was stirred for 0.5 h at 0° C. and for 4 h at room temperature. Then, the reaction mixture was concentrated, the residue was taken up in ethyl acetate and washed with 2 M HCl, aqueous sat. sodium hydrogen carbonate solution and brine. The organic layer was dried over sodium sulphate, concentrated and purified by chromatography on silica (ethyl acetate/heptane) to yield 85 mg of a mixture of the (E)- and (Z)-isomers of 2-methyl-2-{[1-(4-phenyl-but-1-enyl)-naphthalene-2-carbonyl]-amino}-propionic acid methyl ester.
