The dictionary of all ligands currently deposited in the PDB (N=37023) was downloaded and filtered to remove complexes containing metals (N=406), or lacking carbon atoms (N=170), and SMILES with incorrect valances (N=513). The remaining complexes (N=35934) were filtered for ligands with at least one non-aromatic ring of size 7 or larger (N=1557, Figure ), retaining 4% of the total ligands. These molecules have an increased molecular complexity relative to the overall list of deposited ligands (Figure ). Representative examples of high resolution crystal structures of complexes containing randomly selected macrocyclic ligands, and not containing any other cofactors in the site, were selected to approximately reproduce the distribution of ring sizes found in the PDB (N=90, Figure ). Details on the complexes used in this set are available in Table .