Table 4.

Most relevant databases applied frequently in 2D similarity search.

The Searchable Chemical Space
Database	Unique Compounds			References
Zinc library	35 million			[43,44]
Chemspider	58 million			[45]
eMolecules	5.9 million			[46]
The Biologically Relevant Chemical Space
Database	Compounds	Bioactivity or Binding Data	Protein Targets	References
PubChem	91,371,681	232,760,104	n.a.	[47]
ChEMBL	2,036,512	14,371,197	11.224	[48]
Binding_DB	590.985	1,328,228	6.922	[49]