Compared to quinolines, isoquinolines are also prominent structural motifs present in many biologically significant natural and synthetic compounds. Some well-known isoquinoline alkaloids include the anticancer and anticonvulsant berberine, the vasodilator and antispasmodic drugs papaverine and emetine. In addition to naturally occurring isoquinolines, synthetic analogs have also shown significant biological activity.
Thiadiazoles are a subfamily of azoles. Structurally, they are five-membered heterocyclic compounds containing two nitrogen atoms and one sulfur atom, and two double bonds, forming an aromatic ring. Depending on the relative positions of the heteroatoms, there are four possible structures; these forms do not interconvert and are therefore structural isomers rather than tautomers. These compounds themselves are rarely synthesized and have no particular utility, however, compounds that use them as structural motifs are fairly common in pharmacology.