CRBN ligand block is currently a popular block widely used in PROTAC drug development. CRBN ligand blocks typically refer to derivatives of Lenalidomide, Pomalidomide, and Thalidomide, which play important roles in constructing PROTAC molecules.

Bis (aziridine) is a ternary ring structure compound that has attracted much attention due to its outstanding performance in the field of photoaffinity probes. Through UV excitation, biaziridine can highly selectively label target proteins and depict their binding site maps. In drug development, it is widely used for identifying ligand targets, mapping binding sites, studying protein interactions, and live cell imaging.

In drug discovery, medicinal chemists often use the "nitrogen scanning" strategy of aromatic rings to finely construct each nitrogen-containing 5-6 heterocyclic ring in order to find the most effective structure. Therefore, 5-6 heterocycles are highly favored due to their importance and flexibility in drug design, becoming a popular choice in drug building blocks.

When designing inhibitors targeting specific enzymes or receptors, using a five membered heterocyclic ring as an electron withdrawing substitution group can significantly improve the biological activity and selectivity of drugs. Therefore, the five membered heterocyclic block is a favored choice in drug design, usually used in the drug screening process to find the optimal drug skeleton.