3.76 g (19.6 mmol) of EDCl was added to 40 ml of THF solution of 1.99 g (9.79 mmol) of Boc-Aib-OH (manufactured by Sigma-Aldrich Corporation), and 2.03 g (9.79 mmol) of H-Leu-NHPh obtained in Synthesis Example 2-2, followed by stirring for 17 hours at room temperature. After a reaction mixture was concentrated under reduced pressure, the concentrate was extracted by adding water and ethyl acetate. After an organic layer was washed sequentially with a diluted hydrochloric acid, an aqueous solution of sodium hydrogen carbonate and water (one time for each), it was concentrated under reduced pressure, thereby obtaining crude amide. The obtained amide compound was purified by a silica gel column chromatography (hexane/ethyl acetate=5/1 to 1/1 (volume ratio)), thereby obtaining 2.42 g of the product with a yield of 63.1%.
