AiZynthFinder: A Fast Robust and Flexible Open-Source Software for Retrosynthetic Planning

15 June 2020, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


We present the open-source AiZynthFinder software that can be readily used in retrosynthetic planning. The algorithm is based on a Monte Carlo tree search that recursively breaks down a molecule to purchasable precursors. The tree search is guided by an artificial neural network policy that suggests possible precursors by utilizing a library of known reaction templates. The software is fast and can typically find a solution in less than 10 seconds and perform a complete search in less than 1 minute. Moreover, the writing of the code was guided by a range of software engineering principles such as automatic testing, system design and continuous integration leading to robust software. The object-oriented design makes the software very flexible and can straightforwardly be extended to support a range of new features. Finally, the software is clearly documented and should be easy to get started with. The software is available at


Neural Network
Retro-synthesis planning software
Monte Carlo Tree-Search

Supplementary weblinks


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