Rest group variables are defined as the characters 'R', 'X' and 'Z' with or without an index number between 0 and 20. 4) Read modified SMILES using the CDK. 5) Remove explicit hydrogen atoms and return absolute SMILES. By adding the newly generated SMILES with Markush structures to the SMILES strings from pubchem_1 and applying the same filtering criteria as described above, 126,702,705 molecules were selected. Based on this, a diverse set of 250,000 SMILES representing molecules with Markush structures were selected for testing using the MaxMin 50 algorithm. One million molecules were retained to use for validation during development, and the remainder was used as training data (pubchem_2, pubchem_3 see Supplementary Table ).