To a solution of ethyl 4-(((1S,2S)-1-hydroxy-2,3-dihydro-1H,1′H-[2,2′-biinden]-2-yl)methyl)benzoate (18, 200 mg, 0.48 mmol), DCC (120 mg, 0.58 mmol) and DMAP (6 mg, 0.048 mmol) in ethyl acetate (10 mL), was added Fmoc leucine (161 mg, 0.48 mmol) and then stirred at room temperature for 12 h. The solids were filtered, washed with ethyl acetate (25 ml) and the combined filtrate was washed with 1.5 N HCl (25 mL), water (25 mL), brine (10 mL), dried over anhydrous Na2SO4. The organic layer was evaporated under reduced pressure and the residue 1 (250 mg) was dissolved in dry THF (6 mL) and cooled to 0° C. Dimethylamine (6 mL, 20% in THF) was added drop wise and the reaction mixture was slowly allowed to stir at room temperature for 1 h. The reaction mixture was evaporated under reduced pressure and the residue was purified by CombiFlash using 30% ethyl acetate in petroleum ether as an eluent to yield 140 mg (55%) of the title compound as a colorless semi solid.
