Fig. 1. Retrospective comparison of active machine learning with historic data. The algorithm was provided with 6% learning data (21 ChEMBL28 compounds tested for CXCR4 binding and published before 2003) and had to pick from the remaining ChEMBL CXCR4 activity data (light green curve, “active learning”) or the remaining data plus 50 000 compounds assumed to be inactive (dark green curve, “distracted learning”). The maximum ligand efficiency29 discovered using this method is compared to historic data (blue curve; 314 compounds tested).