TEA (1.6 mL) and acetic acid (0.8 mL) were added to a chloroform (13 mL) solution of (2S)-2-[{4-[(4-formylphenyl)ethynyl]benzoyl}(methyl)amino]-N,2-dimethyl-N′-(tetrahydro-2H-pyran-2-yloxy)propanediamide (3.7 g) as obtained in Example 16-(1) and homomorpholine hydrochloride (1.6 g). Under ice cooling, sodium triacetoxyborohydride (2.6 g) was added in divided portions in a nitrogen atmosphere, and the mixture was stirred for 3.5 hours at room temperature. Water and ethyl acetate were added, the mixture was adjusted to pH 7.5 with a 1 mol/L sodium hydroxide aqueous solution, and then the organic layer was isolated. The extract was washed with brine, and dried over anhydrous sodium sulfate. Then, the desiccant was filtered out, and the solvent was distilled off under reduced pressure. The resulting residue was purified by OH type silica gel column chromatography (gradient elution with chloroform/acetone=100/0→60/40, followed by chloroform/methanol=90/10) to obtain (2S)-N,2-dimethyl-2-[methyl(4-{[4-(1,4-oxazepan-4-ylmethyl)phenyl]ethynyl}benzoyl)amino]-N′-(tetrahydro-2H-pyran-2-yloxy)propanediamide (light yellow solid) (3.0 g, 69%).
