Synthesis of parabactin analogues and formation of transition metal complexes of parabactin and related compounds

Abstract

Transition metal complexes of parabactin and its related synthetic spermidine catecholamides which lack the central o-hydroxyphenyloxazoline were studied by the potentiometric titration method, e.s.r. spectroscopy, and fast atom bombardment mass spectrometry (FAB-MS). Direct mass spectral sampling of the parabactin–Fe^III complex in glycerol solution was first achieved by FAB-MS spectrometry, confirming that the composition of the parabactin–Fe^III complex is [Fe(parabactin)]^2– 2Na⁺ and that the iron(III) ion binds with two catechols and an o-hydroxyphenyl-Δ²-oxazoline moiety in NaOH solution. The e.s.r. g value (4.5) of the parabactin–Fe^III complex differed from those (4.3) of the 3 : 1 catechol–Fe^III complex and other parabactin-related catecholamide–Fe^III complexes. These results suggest that the structure of the parabactin–Fe^III complex differs considerably from the regular octahedral structure of the 3 : 1 catechol–Fe^III complex and may have a structure similar to the ferrimycobactin P–Fe^III complex, in which the iron(III) ion lies exposed in a splayed V-shaped cleft and binds with five oxygens and one nitrogen in a very strained octahedron.