In the development of central nervous
system (CNS) drugs, the blood–brain
barrier (BBB) restricts many drugs from entering the brain to exert
therapeutic effects. Although many novel delivery methods of large
molecule drugs have been designed to assist transport, small molecule
drugs account for the vast majority of the CNS drugs used clinically.
From this perspective, we review studies from the past five years
that have sought to modify small molecules to increase brain exposure.
Medicinal chemists make it easier for small molecules to cross the
BBB by improving diffusion, reducing efflux, and activating carrier
transporters. On the basis of their excellent work, we summarize strategies
for structural modification of small molecules to improve BBB penetration.
These strategies are expected to provide a reference for the future
development of small molecule CNS drugs.