The structure of enterochelin and related 2,3-dihydroxy-N-benzoyne conjugates from Eschericha Coli

Five compounds, each containing 2,3-dihydroxybenzoic acid and serine, have been isolated from culture media of Escherichia coli and Aerobacter aerogenes grown under conditions of iron deficiency. Evidence for the structure of each of these compounds is presented. One of the compounds is a cyclic trimer of 2,3-dihydroxy-N-benzyol-l-serine, which on treatment with aqueous base, gives rise to the other four compounds found in culture supernatants: 2,3-dihydroxy-N-benzoylserine; N,N′-bis(2,3-dihydroxybenzoyl)-O-seryl serine; N,N′, N″-tris(2,3-dihydroxybenzoyl)-O-seryl-O-seryl serine, and a nonhydrolytic cleavage product N,N′, N″-tris(2,3-dihydroxybenzoyl)-O-(α-aminoacrylyl)-O-seryl serine. The cyclo-tris(2,3-dihydroxy-N-benzoylseryl), for which the trivial name enterochelin is suggested, has steric properties which enable it to complex with a metal ion as a hexadentate ligand through the phenolic groups.