FIGURE 1  Chemical structures of melatonin and ramelteon

From the following article:

Drug Insight: the use of melatonergic agonists for the treatment of insomnia—focus on ramelteon

Seithikurippu R Pandi-Perumal, Venkataramanujan Srinivasan, Burkhard Poeggeler, Rüdiger Hardeland and Daniel P Cardinali

Nature Clinical Practice Neurology (2007) 3, 221-228
doi:10.1038/ncpneuro0467