To solution containing (E)-3-(1-(tert-butoxycarbonyl)-1H-indol-3-yl)acrylic acid (200 mg, 0.696 mmol), 3-hydroxy-N′-isopropylbenzohydrazide (202.81 mg, 1.04 mmol) and HATU (397.02 mg, 1.04 mmol) dissolved in DMF (7.0 ml), N,N-diisopropylethylamine (DIPEA) (0.1819 ml, 1.04 mmol) was slowly drop-wise added and stirred at room temperature for 12 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 (28% EtOAc) and dried so that ivory (E)-tert-butyl 3-(3-(2-(3-hydroxybenzoyl)-1-isopropylhydrazinyl)-3-oxoprop-1-enyl)-1H-indole-1-carboxylate was obtained (54 mg, 16.7%).
