scaffold hopping

Scaffold hopping means swapping out the central frame of a molecule while keeping the important business ends in the same places. Picture a chair: you can replace the entire frame with a completely different design as long as the seat and back stay where a person needs them. The new molecule looks different but does the same job.

The scaffold is the core ring system or backbone that holds the activity-driving groups in their proper geometry. In scaffold hopping, chemists design a new core that positions those key groups equivalently but is chemically unrelated to the old one. The pharmacophore is preserved while the connecting framework changes entirely.

Chemists do this for very practical reasons: to escape a competitor's patent, to fix a metabolic or toxicity liability baked into the old core, or to improve solubility and physicochemical behavior. The risk is that the new scaffold subtly shifts the geometry, so a promising hop on paper can lose potency in practice and must be confirmed experimentally.