Active Retrosynthetic Planning Aware of Route Quality

Retrosynthetic planning is a sequential decision-making process of identifying synthetic routes from the available building block materials to reach a desired target molecule. Though existing planning approaches show promisingly high solving rates and route qualities, the trivial route quality evaluation via pre-trained forward reaction prediction models certainly falls short of real-world chemical practice. An alternative option is to annotate the actual quality of a route, such as yield, through chemical experiments or input from chemists, but this often leads to substantial query costs. In order to strike the balance between query costs and route quality evaluation, we propose an Active Retrosynthetic Planning (ARP) framework that remains compatible with the established retrosynthetic planners. On one hand, the proposed ARP trains an actor that decides whether to query the quality of a reaction; on the other hand, it resorts to a critic to estimate the value of a molecule with its preceding reaction quality as input. Those molecules with high reaction qualities are preferred to expand first. We apply our framework to different existing approaches on both the benchmark and an expert dataset and demonstrate that it outperforms the existing state-of-the-art approach by 6.2% in route quality while reducing the query cost by 12.8%. In addition, ARP consistently plans high-quality routes with either abundant or sparse annotations.