ChEBI

ChEBI is a freely available, open source bioinformatics and cheminformatics resource that provides manually annotated information on ‘small’ chemical entities – constitutionally or isotopically distinct atoms, molecules, ion pairs, radicals, radical ions, complexes, conformers, or anything else that is a distinguishable entity. In biology, metabolites are a typical example of small molecules. Molecules directly encoded by the genome (e.g. nucleic acids, proteins and peptides derived from proteins by cleavage) are not as a rule included in ChEBI.