Fig. 6

Illustration of the identification of a reactive center for the Diels–Alder reaction. The colors refer to the general section of the algorithm where the step is performed: database interpretation (red), mapping (blue), extraction (green) and formalizing the template (yellow). Starting from the interpreted reaction, the first two steps allow for the extraction of the reactive center. Step 3 formalizes the identification of the reactive center for the template. First the SMILES identifier is generated. In a second step the number of neighbors (‘X3’ implies three neighbors), the valence (v4 implies a valence of 4, i.e. a non-radical carbon atom) of each atom are added to the identifier to arrive at the SMARTS identifier. Finally SMARTS and labels are generated for each of the atoms in the reactive center, with the described atom listed first. This information is then combined with the recipe for the reaction into the template