Figure shows the price distribution of all building block molecules. Price of approximately 1/10 th of all molecules from ChemSpace range from 10 ! to 10 " USD/g, which is unreasonably expensive. Therefore, these molecules were removed from the set of building blocks to lower the costs of the potential synthetic routes. In total, we selected 24,282 commercially and 451 naturally available building blocks respectively. A full list of building block molecules can be found in the Supporting Information (SI).