Fig. 1

Multistep search process. All target molecules (red) are initiated simultaneously. At the first iteration, K sets of reactants are proposed for each target molecule, for each set of proposed reactants a reaction node (grey) is added followed by the relevant reactants (blue). The n most promising molecule nodes (circled in dark blue) are followed up, and K sets of reactants are proposed for each, with the same process continued iteratively until all end nodes are building blocks (yellow) or the time or iteration limit is reached. The retrosynthetic routes are then extracted from the search graph. The hypothetical example shown consists of two target molecules, with three sets of reactants proposed for each molecule node (K) and four molecule nodes (n) followed up with a maximum of two iterations. Only a sample of the potential extracted routes is shown