To the non-specialist in medicinal chemistry (like myself), the abundance of drugs that contain aromatic ring moieties, usually with heteroatoms like N, is somewhat surprising. In fact, in 2012, the top 4 out of 5 drugs by sales contain such groups.
There are at least a few good reasons why these types of compounds appear so often:
1 Heterocyclic systems are easier to prepare synthetically than all-carbon based aromatic systems and they are easier to modify later.
2 Scaffolds with heterocycles allow the easy introduction of H-bond donors and acceptors to fine-tune the properties of the compound, like binding affinity, solubility, and resistance to metabolism in vivo.
3 Can “template hop” easily off of aromatic ring scaffolds to evolve new IP with the same functionality as a known drug (e.g., Viagra to Levitra).
Can synthetic chemistry specialists give more reasons? (Post in the comments!)
Source: Jordan, A, Roughley, S. “Drug discovery chemistry: a primer for the non-specialist.” Drug Disc Today, 14. 2009