Whereas it has been estimated as there are theoretically more than 10 60 small organic molecule chemical structures , the number of molecules actually explored in drug discovery is limited to about 10 8 at most . To efficiently propose new molecules with desirable physicochemical properties from a wide chemical space, an artificial intelligent (AI) technique called molecular generative model has been studied in recent years . As an input of the AI model, the chemical structure is represented in two ways: SMILES and a molecular graph . In general, molecular graphs are more robust and precise to represent the molecular features than SMILES, because graph representations can capture the molecular similarity and can consider chemical checks, such as protecting the number of valence electrons, unlike SMILES representations .