There are human diseases which involve a toxic iron overload (hemochromatosis) and are treated by chelation therapy. The siderophore enterobactin, produced by E. coli, exhibits the largest binding constant fo ferric ion of any natural substance. It is composed a tri-L-serine lactone nucleus to which are appended three exocyclic 2,3-dihydroxybenzamide units which serve as the binding ligands for Fe(III). However, the compound is unsuitable as a therapeutic agent as it promotes the growth of E. Coli. Ye its structural components are of interest in the design of derivative ligands which may offer some therapeutic advantage. The synthetic enterobactin analogs which have been prepared to date exhibit lower binding constants towards ferric ion than enterobactin, presumable because: the three catechol binding units in these ligands are not preorganized towards binding; and the ligand backbones become quite straine as a consequence of binding ferric ion. The goals of this research are the synthesis, complexation, and chemical evaluation of new catechol ligands which are structurally related to enterobactin. These compounds are of interest because they could be excellent ferric ion binders; because they could provide insights as to why enterobactin is so exceptional a ligand; and because they could serve as probes for the elucidation of some of the details of the biological transport of enterobactin into the bacterial cell. The compounds to be made include the derivative of enterobactin wherein the lactone carbonyls have been reduced to methylenes, forming a symmetric 12- crown-3 nucleus; and an enterobactin analog where L-threonine rather than serine is used in the trilactone backbone (the enterobactin molecule with a additional methyl group at each ester beta-carbon). We also propose to mak the saturated derivative of the enterobactin analog MECAM, which because of its closer spatial similarity to enterobactin, should be a better ligand fo Fe(III). Other proposed ligands are related to enterobactin, yet contain 2,3- dihydroxterephthalate binding subunits which have lower pKa's and should be better iron binders at physiological pH than the 2,3-dihydroxybenzamide units in enterobactin. These include the terephthalamide derivative of enterobactin (and the deoxygenated derivative). These macrobicyclics shoul be particularly stable complexes with Fe(III) as the entropy loss on bindin should be less for macrobicyclic ligands, with their preformed binding cavities, than for acyclic ligands. The main thrust of this proposal is synthetic, and focuses on the preparation and chemical analysis of the proposed ligands. In addition, x- ray crystallographic determination; solution thermodynamics; and biological uptake and transport studies will be done in collaboration with Professor Kenneth R. Raymond of the University of California, Berkeley.
