The neurohormone melatonin (5-methoxy-N-acetyltryptamine, 1), which is mainly secreted from the pineal gland or chemically synthesized, is putatively involved in several physiological processes including circadian rhythms, retinal physiology, seasonal breeding, and cardiovascular regulation. 1–3 Since the therapeutic efficacy of melatonin is limited by its short biological half-life, analogs of melatonin were designed and synthesized. It is ...