Structure of Pseudobactin A, a Second Siderophore from Plant Growth Promoting Pseudomonas B10

The structure of nonfluorescent pseudobactin A, one of two extracellular siderophores (microbial iron transport agents) produced by the plant growth promoting bacterium Pseudomonas B10, was determined by comparison of its 1H and 13C NMR spectra with those of yellow-green, fluorescent pseudobactin, the other siderophore. The molecular and crystal structure of ferric pseudobactin is reported in the preceding paper in this issue [Teintze, M., Hossain, M. B., Barnes, C. L., Leong J., & van der Helm, D. (1981) Biochemistry (preceding paper in this issue)]. The only structural difference between pseudobactin and pseudobactin A was that the latter was saturated at carbons 3 and 4 of the quinoline derivative, whereas pseudobactin is unsaturated at these positions. A mechanism is proposed for the observed conversion of pseudobactin A into pseudobactin in aqueous solution.