Synthesis of optically pure chrysobactin and immunoassay development

Chrysobactin (-N-(2,3-dihydroxybenzoyl)-d-lysyl-l-serine), a siderophore that is essential for systemic virulence by plant pathogenic Erwinia chrysanthemi, was synthesized with high diastereomeric purity. Chrysobactin was prepared by coupling the N-hydroxysuccinimide ester of -N-(2,3-dibenzyloxybenzoyl)--N-Cbz-d-lysine with l-serine benzyl ester followed by deprotection via hydrogenolysis. Optically pure chrysobactin was obtained with 98% overall yield. A monoclonal antibody to ferric chrysobactin was developed and characterized as IgM. The antibody reacts with chrysobactin, ferric chrysobactin and less strongly with ferric dihydroxybenzoic acid. The antibody reacts weakly with the siderophores ferrichrome, A, ferric pseudobactin and ferric rhodotorulic acid. This antibody was used in a competitive immunoassay to detect ferric chrysobactin at 10^–8 to 10^–10 mol. This immunoassay may provide a useful method for the detection of chrysobactin in plant samples.