“…Oxygen-containing heterocycles as those of the nitrogen analogues are widely present in various kinds of natural products, such as carbohydrates, polyketides, peptides, and terpenoids, which show large potential of diverse pharmacological properties [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Nature-derived O-heterocycle pharmaceuticals salinomycin and Taxol are used to treat cancer, artemisinin is effective antimalarial agent, digoxin is a cardiac glycoside, and has inotropic effects in addition to effects on cardiac output, and codeine and morphine are opioid drugs [ 23 ].…”