Structures of Two Polyamine-Containing Catecholate Siderophores from Vibrio fluvialis

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From low-iron cultures of Vibrio fluvialis AQ 0012, two new compounds with siderophore activity were purified by XAD-7 adsorption followed by preparative TLC. Norspermidine and 2, 3-dihydroxybenzoic acid were identified as constituents common to both compounds by GC-MS analyses of their acid hydrolytic products. In addition, L-threonine was identified in the hydrolysate of one compound, named fluvibactin. Based on high magnetic NMR analyses, the structure of fluvibactin was established as N⁴- [2-(2, 3-dihydroxyphenyl)-trans-5-methyl-2-oxazoline-4-yl] carboxy-N¹, N⁷- bis-(2, 3-dihydroxybenzoyl)-norspermidine, and that of the other compound as N¹, N⁷- bis-(2, 3-dihydroxybenzoyl)-norspermidine. The structures were supported by fast atom bombardment mass spectrometry. Both of the purified compounds restored growth inhibition of the producer strain and V. cholerae Non-O1 induced by ethylenediamine di-(o-hydroxyphenylacetic acid), a potent synthetic chelating agent of ferric iron.