Field Notes
Structure-based drug design methodology, fragment-based lead discovery, docking validation, and hit identification strategy — written for discovery chemists and computational biologists.
High-throughput screening libraries optimize for diversity metrics that have little relationship to the geometry of a specific binding pocket. Fragment-based approaches start from the other direction — and the hit quality difference is measurable.
Docking is fast; FEP is accurate. Neither is universally correct for hit triage. The choice depends on what you know about the target binding mode and how much structural uncertainty you can tolerate at the hit stage.
Most hit-to-lead programs stall not because the hits were weak but because the structural basis for potency was never established. Designing the campaign around structural constraints from week one changes what questions you ask — and which hits you keep.
The published crystal structure shows one conformation. The therapeutically relevant binding event may involve a pocket that only opens transiently during protein dynamics. Conformational sampling methods now make these cryptic pockets accessible for structure-guided campaigns.
Selectivity failures are most expensive when they appear late — in cell-based assays or in vivo studies. Structural selectivity analysis at the hit identification stage can predict off-target liabilities before a compound touches a cell.
An AUC-ROC of 0.8 on a DUD-E benchmark does not mean your virtual screen will find three kinase hits in a library of ten thousand compounds. What enrichment metrics measure, what they miss, and how to set realistic expectations before a campaign starts.
Covalent drugs are no longer a last resort. Structure-guided warhead selection — matching electrophile reactivity to the target cysteine microenvironment — is now a tractable hit identification strategy for the right target class.
GPCRs are among the most clinically validated target classes, yet structure-guided agonist campaigns fail more often than antagonist campaigns at the hit identification stage. The conformational dynamics of the orthosteric binding site, not the quality of the docking model, is usually the reason.
Fragment elaboration produces one chemical series. Scaffold hopping asks what other molecular frameworks could occupy the same binding site with different pharmacokinetic properties or IP positioning. Structure guides both questions.