To (S)-2-Amino-4-[4-(4-benzoylamino-phenoxy)-6-methoxy-quinolin-7-yloxy]-butyric acid cyclopentyl ester (37 mg, 0.066 mmol) in anhydrous methanol (1 ml) were added 100 μL of a 1 M solution of isobutyraldehyde in methanol and 1 drop of acetic acid. The reaction mixture was stirred at room temperature for 3 hours. Sodium cyanoborohydride (10.3 mg, 0.165 mmol) was then added and the reaction was left stirring 4 hours at room temperature, prior to concentration under vacuum. Purification by preparative HPLC afforded the title compound as a di-TFA salt (40 mg, 72% yield).
