Exploring Privileged Structure Repurposing: Target Similarity as a Catalyst for Cross-Species Drug Discovery.

Privileged drug structures refer to substructures that impart drug-like properties, including high target affinity, favorable pharmacokinetic profiles, and structural modifiability. In cross-species drug repositioning, targets should be prioritized based on homologous proteins that exhibit high structural and functional conservation across members of the same virus family. Subsequently, validated, safe, and druggable privileged structures must be identified. Thereafter, computational chemistry and structural biology approaches are systematically employed to evaluate the structure's potential binding affinity and mode of interaction with the newly identified disease-relevant target. In this phase, three core medicinal chemistry strategies, including side-chain replacement, conformational constraint, and scaffold hopping, are applied to optimize the lead compound. We validate this strategy through representative case studies and summarize key practical challenges: off-target toxicity and difficulties in modifying privileged scaffolds. Leveraging their advantages while innovating repositioning methods can improve drug development efficiency, quality, and responsiveness to unmet clinical needs.