Ectoine is a carboxamidine heterocycle obtained by formal condensation of (2S)-2,4-diaminobutanoic acid with acetic acid. It has a role as an osmolyte. It is a carboxamidine, a member of 1,4,5,6-tetrahydropyrimidines and a monocarboxylic acid. It is a conjugate acid of an ectoinate. It is a tautomer of an ectoine zwitterion.