The Chemical Entities of Biological Interest (ChEBI) ontology is downloaded weekly from EMBL-EBI at http://www.ebi.ac.uk/chebi/. The data is made available under the Creative Commons License (CC BY 3.0, http://creativecommons.org/licenses/by/3.0/). For more information see: Degtyarenko et al. (2008) ChEBI: a database and ontology for chemical entities of biological interest. Nucleic Acids Res. 36, D344–D350.
Originally referring to an endogenous compound that is formed in specialized organ or group of cells and carried to another organ or group of cells, in the same organism, upon which it has a specific regulatory function, the term is now commonly used to include non-endogenous, semi-synthetic and fully synthetic analogues of such compounds.