Crystal structure of (1 S ,2 S ,2′ R ,3a′ S ,5 R )-2′-[(5-bromo-1 H -indol-3-yl)methyl]-2-isopropyl-5,5′-dimethyldihydro-2′ H -spiro[cyclohexane-1,6′-imidazo[1,5- b ]isoxazol]-4′(5′ H )-one