Synthesis of the studied coumarin compounds (C87G–N). Reagents: (a) HBr; (b) 2-(Boc-amino)ethyl bromide; (c) CF3COOH; (d) DCC, (3,5-difluorophenyl)acetic acid, 3,5-difluorocinnamic acid, 3,4-difluorodihydrocinnamic acid or 3,4-dichlorocinnamic acid [15]