Pretraining & Transfer learning Before guiding a generator to create compounds with specific properties, it needs to be pretrained to learn the language of drug-like molecules and be able to generate reasonable molecules. This in-volves training a generator to reproduce compounds from a large set of (fragmented) drug-like molecules. We have shared pretrained RNN-based and transformer-based generators (pretrained on ChEMBL27, ChEMBL31 18 and Papyrus v5.5 ) on Zenodo. 20 Further details about the pretrained models are given in section S1 and section S4.