ISOLATION AND STRUCTURE OF RHIZOBACTIN-1021, A SIDEROPHORE FROM THE ALFALFA SYMBIONT RHIZOBIUM-MELILOTI 1021

Rhizobactin 1021, a novel siderophore from the nitrogen-fixing alfalfa symbiont Rhizobium meliloti 1021, was isolated and structurally characterized by a combination of chemical and spectroscopic techniques. The compound is a citrate derivative in which the distal carboxyl groups of the molecule are amide linked to two different side chains. One of these is 1-amino-3-(N-hydroxy-N-acetylamino)propane, and the other is 1-amino-3-(N-hydroxy-N-(E)-2-decenylamino)propane. The structure of rhizobactin 1021 was determined as (E)-4-[[3-(acetylhydroxyamino)propyl]-amino]-2-hydroxy-2-[2-[3-[hydroxy(1-oxo-2-decenyl)amino]propyl]amino]-2-oxobutanoic acid. acid. Ferric rhizobactin 1021 exists in solution predominantly in the LAMBDA configuration, in an apparent equilibrium between a monomeric and a dimeric species.