A Quick Policy to Filter Reactions Based on Feasibility in AI-Guided Retrosynthetic Planning

A neural network-guided Monte Carlo tree search (MCTS) has been shown to be a promising algorithm for computer-aided synthesis prediction. Here we train and investigate a filter policy that removes unfeasible reactions from the search. We investigate three different methods to generate negative data that the filter policy model can be trained on, and we show that these methods are complementary to each other. Therefore the most robust model is one that combines all generated negative data. The filter in itself is quick (<0.1 s per prediction on average) but using the filter policy in the MCTS results in a doubling of the search time. However it only leads to a small reduction in the success rate of finding synthetic routes (<1%) and we are able show that using filter policy the MCTS algorithm produce more promising routes, although the predicted routes are more complex. The filter policy has been integrated in the AiZynthFinder software.