An investigation of desferrithiocin metabolism

The hydrolyses of (S)-desferrithiocin (DFT, 1), (R)-desmethyl-DFT (2), and (R)-desazadesmethyl-DFT (3) were studied at pH 2.5 and 7.2 in order to access the stability of the thiazolines at the pH of the stomach and the serum. At 37 degrees C and pH 2.5, DFT (1) (t1/2 = 18.6 h), desmethyl-DFT (2) (t1/2 = 8.74 h), and desazadesmethyl-DFT (3) (t1/2 = 31.7 h) were shown to open principally to the thiol amides with trace amounts of the corresponding thioesters, < or = 2%. The thiazolines were resistant to hydrolysis at pH 7.2. Iron(III) stabilized significantly the thiazolines in the complexes 16a/b of 3 in regard to hydrolysis at pH 2.5 (t1/2 > 20 days). The iron(III) complexes 16a/b were shown to be stable at pH 7.2. While the thiol amides 13 and 14 of 1 and 2 were isolated from the hydrolysis of the parent desferrithiocins, the thioester 4 and the thiol amide 5 of 3 were synthesized and their stability in aqueous solution, iron-clearance properties, and toxicity were evaluated. Thioester 4 was shown to rearrange to thiol amide 5 at pH 2.5 and 37 degrees C with a half-life of 4.18 h and instantaneously at pH 7.2. Thiol amide 5 is in equilibrium with 4 (5/4 = 49:1) at pH 2.5 and was shown to be stable at pH 7.2. Thioester 4 and thiol amide 5 demonstrated neither iron-clearance activity in iron-overloaded rats nor toxic side effects in mice. Hydrolysis products of the drug, which might be generated in the stomach, seem unlikely to be the source of the drug's toxicity or iron-clearing properties.