Enamine (Kyiv, Ukraine, enamine.net) provided structural details of 155,129 BBs that were in stock as of December 2019. These BBs were standardized to remove fragments and salts. Duplicates were removed via a stereo-sensitive and tautomer-sensitive unique CACTVS hashcode identifier calculated for each building block. Further filters were applied to remove BBs containing less abundant isotopically labelled atoms, metals, as well as structures that were too complex to yield reasonable screening compounds, with the complexity quantitatively defined according to a modified Bertz/Hendrickson algorithm . This left us with 152,532 structures. They were used to generate SAVI reactant pairs for application of the transform logic. Reactant pairs that might lead to a reaction forming polymers and/or product mixtures were excluded from the execution.