• Rank Score: the Kendall's tau score τ between the Tanimoto similarity and the NLL for the top ten compounds sampled by beam search. The score measures the correspondence between the two rankings. The score have values in [-1, 1] range, where the extremes denote perfect disagreement and agreement, respectively. Given a source compound s and N generated compounds t1 , . . . , tN from s, τ is computed as: