AI Retrosynthesis Planning

Retrosynthesis works backward from a target molecule. A system predicts one or more sets of precursor molecules that might react to form the target, then repeats the process on those precursors until it reaches available starting materials or a stopping condition. AI methods can help propose reaction disconnections and organize a search tree, while chemists assess whether the steps make practical sense. Template-based systems apply learned or curated reaction patterns to identify bonds and functional groups that may transform. Template-free systems predict products or precursors more directly from molecular representations. Both depend on training data, reaction coverage, and standardization. Reaction databases overrepresent published and successful chemistry, may omit conditions or yields, and can have inconsistent atom mapping or stereochemistry. A planning system usually ranks multiple routes rather than returning one definitive synthesis. Search may consider route length, predicted reaction likelihood, starting-material availability, cost, safety, and operational constraints. A short route can still require expensive or unstable reagents. A high model score can reflect familiar reactions but overlook purification, selectivity, scale-up, or hazardous conditions. Evaluate retrosynthesis with more than exact match. Top-k accuracy asks whether a reference precursor appears among predictions, but alternative valid routes may differ from literature. Route-level quality depends on every step and practical execution. Forward reaction prediction can provide an additional consistency check, yet it is also model-based and not proof that the reaction will work. AI planning can prioritize ideas and help chemists explore reaction space, but it cannot substitute for expertise or lab work. Check commercial availability, safety data, reaction conditions, stereochemistry, and route reproducibility. Treat proposed routes as hypotheses that need a chemist's review and experimental validation.