(S)-4,5-dihydro-2-(2-hydroxy-4-hydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid polyethers: a solution to nephrotoxicity.

Previous studies revealed that within a family of ligands the more lipophilic chelators have better iron-clearing efficiency. The larger the log P(app) value of the compound, the better the iron-clearing efficiency. What is also clear from the data is that although the relative effects of log P(app) changes are essentially the same through different families, there are differences in absolute value between families. However, there also exists a second, albeit somewhat more disturbing, relationship. In all sets of ligands, the most lipophilic chelator is always the most toxic. The current study focuses on designing ligands that balance the lipophilicity/toxicity problem while iron-clearing efficiency is maintained. Earlier studies with (S)-4,5-dihydro-2-(2-hydroxy-4-methoxyphenyl)-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(CH(3)O)-DADFT, 6] indicated that this methyl ether was a ligand with excellent iron-clearing efficiency in both rodents and primates; however, it was too toxic. On the basis of this finding, a less lipophilic, more water-soluble ligand than 6 was assembled, (S)-4,5-dihydro-2-[2-hydroxy-4-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT-PE, 11], a polyether analogue, along with its ethyl and isopropyl esters. The parent polyether and its isopropyl and ethyl esters were all shown to be highly efficient iron chelators in both rodents and primates. A comparison of 11 in rodents with the desferrithiocin analogue (S)-4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT, 1] revealed the polyether to be more tolerable, achieving higher concentrations in the liver and significantly lower concentrations in the kidney. The lower renal drug levels are in keeping with the profound difference in the architectural changes seen in the kidney of rodents given 1 versus those treated with 11.