Analyzed synthetic accessibility scores SAscore SAscore is designed as a synthetic accessibility score of drug-like molecules for virtual screening exploration. It is calculated as a sum of fragment scores and complexity penalty. Fragment score is based on statistics of the frequency of Extended Connectivity Fingerprints of diameter 4 (ECFP4) fragments from Pipeline Pilot on almost one million molecules obtained from the PubChem database . ECFP is a method of creating a numeric representation of a chemical structure by traversing it, enumerating atoms, and hashing their representation. The aim of the fragment score is to capture if fragments observed previously in the database are present in the analyzed molecule. The complexity penalty aims to capture if a molecule does not contain too many complex structures to be Internal nodes have a non-empty list of expandable molecules, but their depth is below a predefined depth. Solved nodes are leaves with all molecules in the in-stock list. A leaf marked as not solved means that it contains at least one expandable molecule and its depth exceeds a predefined threshold. Because we aim to discriminate promising nodes from non-promising ones as early as possible, we define a not solved node as all nodes that have no path to a solved leaf. In the majority of cases, we focus on roots of subtrees of not solved nodes.