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.
Tetrahydropyran is an organic compound consisting of a saturated six-membered ring containing five carbon atoms and one oxygen atom. Tetrahydropyrans are common structural motifs in natural products and synthetic therapeutic molecules. In nature, these six-membered oxygen heterocycles are usually assembled by intramolecular reactions, including oxygen Michael addition or ring opening of epoxy alcohols. In fact, polyether natural products have been particularly extensively studied for their fascinating structures and important biological properties; these are often formed through endoselective epoxy open cascades.