By analogy to the previously reported analysis, the most frequent connection between two NP fragments in ChEMBL-PNPs is the linear connection (connection monopodal (cm)), followed by an edge fusion (fusion edge (fe)), a bridge fusion (fb), a spiro fusion (fs) and the bipodal edge connection (cbe; for a graphical representation of the different fusion and connection types, see figure and ref. ). The relative distribution of the different connection and fusion types is cm:fe:fb:fs:cbe ≈ 100:22:5:3:2.5. Fig. shows the most abundant fragments found in PNPs, while fig. displays the most common combination of fragments, including their connection types. For future widespread application and exploration of PNPs in medicinal chemistry and chemical biology programs, uncomplicated and fast access to different PNP classes without the need to launch and execute lengthy synthesis programs would be instrumental. The Enamine collection of currently ca. 3.5 million compound collection is a rich source of structurally diverse small molecules and is frequently sourced for research and discovery by industry and academia. Given the fact that PNPs have been synthesized frequently before (see above), probably driven by intuitive inclusion of NP structures in compound library design, we speculated that this very large library also might contain a substantial number of PNPs.