The drug design process can be thought of as a multiobjective optimization problem in which potential drug compounds need to satisfy a wide set of properties from binding affinity and toxicity to selectivity and solubility . One property that is key when developing potential drug molecules is their availability, since no matter how promising a design might be, if it is not available, it is doomed to fail. In order to estimate compound availability, several computationally calculated synthetic accessibility (SA) scores have been developed. These approaches can be roughly classified as retrosynthesis-based predictions , binary classifiers , and complexity-based estimations . Retrosynthesis-based approaches aim to identify suitable synthetic routes for a given molecule using distinct types of search algorithms over databases of building blocks and chemical transformations.