For the REINVENT loop, we set the number of epochs N steps to 250 and we keep the default value of 128 for batch size P . The hyperparameter λ in the REINVENT loss function (Equation ) is also set to 128 by default. The scoring function comprises a single component which corresponds to the pre-trained RFR to which a double sigmoid transformation is applied to map the estimated LogP values to [0, 1], such that values lying within the desired range of result in transformed scores close to 1 (i.e., high reward scores). This double sigmoid transformation is illustrated in Appendix C.