1.4. ChEBI: a dictionary of small molecular entity

        ChEBI (https://www.ebi.ac.uk/chebi/)^13,14 stands for “Chemical Entities of Biological Interest”.  It is a freely available database of “small” molecular entities, developed at the European Bioinformatics Institute (EBI).  The molecular entities in ChEBI are either natural or synthetic products used to intervene the processes of living organisms.  As a rule, however, ChEBI does not contain macromolecules directly encoded by genome (e.g., nucleic acids, proteins, and peptides derived from protein by cleavage).  ChEBI provides “standardized” descriptions of molecular entities that enable other databases to annotate their entries in a consistent fashion. ChEBI focuses on high-quality manual annotation, non-redundancy, and provision of a chemical ontology rather than full coverage of the vast chemical space.  Note that both ChEMBL and ChEBI are developed and maintained by the EMBL-EBI.  While ChEMBL focuses on “bioactivity” of a large number of bioactive molecules (currently ~1.7 millions), ChEBI is a “dictionary” that provides high-quality standardized descriptions for a relatively small number of molecules (currently ~50 thousands).