To solution containing (E)-3-(1-(3-methylbut-2-enyl)-1H-indol-3-yl)acrylic acid (160 mg, 0.62 mmol, 1.0 equivalent), N′-isopropylbenzohydrazide (167.5 mg, 0.94 mmol, 1.5 equivalent) and HATU (357.4 mg, 0.94 mmol, 1.5 equivalent) dissolved in DMF (5.0 ml), N,N-diisopropylethylamine (DIPEA)(0.16 ml, 0.94 mmol, 1.5 equivalent) was slowly drop-wise added and stirred at room temperature for 24 hr. The reaction mixture was diluted with EtOAc, washed with water and brine, dried with anhydrous MgSO4, filtered, and concentrated under reduced pressure. The residue was separated through silica gel chromatography (n-hexane:EtOAc=1:1) and dried so that yellow solid form of (E)-N′-isopropyl-N′-(3-(1-(3-methylbut-2-enyl)-1H-indol-3-yl)acryloyl)benzohydrazide was obtained. (99.8 mg, 39%).
