Pyrimidine, also known as 1,3-diazobenzene, is a heterocyclic compound with the chemical formula C4H4N2. Pyrimidine is formed by substituting 2 nitrogen atoms for 2 carbons in the meta-position of benzene. It is a diazine and retains its aromaticity. Derivatives of pyrimidine widely exist in organic macromolecular nucleic acids, and many drugs also contain pyrimidine rings. In nucleic acids, three nucleobases are pyrimidine derivatives: cytosine, thymine and uracil. There are a variety of pyrimidine-containing drugs on the market, most of which are kinase inhibitors.
Oxygen heterocycles are one of the most common heterocycles in drugs and natural products. Oxetene has high polarity and is also a good acceptor for hydrogen bond, which contributes to the metabolism and chemical stability of its host molecules. When substituted for commonly used functional groups such as gem dimethyl or carbonyl, oxetane units can induce profound changes in water solubility, lipophilicity, metabolic stability and conformational preference. Four of the FDA-approved drugs contain oxetenes: Orlistat, Paclitaxel, and two of its derivatives, Docetaxel and Cabazitaxel. Currently, oxetane-containing building blocks are flourishing in medicinal chemistry and drug discovery.