Most of the chelating groups were not represented in the investigated screening libraries and chemical spaces (Tables and). This is mainly caused by the low presentation or absence of phosphor-containing compounds. As these libraries have been designed with drug discovery in mind and phosphate, due to its high charge and bad permeability, is typically not wanted in screening libraries, the low presentation of these groups is actually positive. Overall, the investigated libraries and chemical spaces are well suited for the discovery of metalloenzyme inhibitors. Notabl y, about the same number of metal-chelating groups were present in a chelator library of under 6,500 compounds (255 matches, 36% of metal-chelating groups without a phosphorus atom, S6 of the Supporting Information) and a chemical space of over 12 billion virtual products (282 matches, 40% of the non-phosphor-containing groups, Table ). Moreover, 190 of these metal-chelating groups are common to both sets. In the Otava chelator fragment library metal-chelating groups were also well represented with 196 matches (Supporting Information S6). The largest investigated space, the REAL space with over 34 billion of virtual products had the highest number of matches (766), however this increase was partly caused by phosphorus-containing groups that are absent from the rest. While a fair number of the extracted metal-chelating groups were well represented, it is evident that there is still room for improvement. This can be achieved by increasing the presence of attractive chelating groups that currently are absent and by striving for a more balanced representation of the groups already present in these libraries and spaces.