Recombination was deemed complete if either the molecule had no dummy atoms left to another subpocket (excluding pool X), the molecule's remaining dummy atoms could not be replaced by any matching fragment, or the molecule consisted of 4 fragments. This upper limit of occupied subpockets was introduced, since the majority of kinase ligands occupies only up to 4 subpockets (see Figure .A) and molecules occupying more subpockets will mostly not fulfill the requirements of a drug-like molecule due to their size (e.g. Lipinski's rule of five ). Finally, if the resulting recombined molecule contained any remaining dummy atoms, they were replaced with hydrogen atoms. This recombination strategy produced over 6.7 million ligands based on 624 fragments.