Design of an i.v. formulation of an unstable prodrug candidate for prostate cancer treatment: solution chemistry of N-(glutaryl-hyp-ala-ser-cyclohexylglycyl-gln-ser-leu)-doxorubicin.

The chemical degradation of N-(glutaryl-hyp-ala-ser-cyclohexylglycyl-gln-ser-leu)-doxorubicin (henceforth referred to as doxorubicin peptide conjugate 1) was studied in buffered aqueous solution. The pH-rate profile of degradation shows that the doxorubicin conjugate is most stable between pH 5 and 6. The dependence of log k(obsd) on pH in acidic medium is characteristic of specific acid-catalysis of the sugar hemiaminal of 1 (as in the case of doxorubicin). Isolation of degradates and structural determination shows that the degradation at lower pH values yields the water-insoluble aglycone doxorubicinone, supporting the mechanism of acid-catalyzed loss of the amino sugar. At pH higher than 5, a more complicated degradation pattern is observed, including the loss of the amino sugar and the aromatization of the saturated ring to give 7,8-dehydro-9,10-desacetyldoxorubicinone as one of the major products. Around the pH of maximum stability in solution, the rate of degradation of 1 is significantly greater than that for doxorubicin, which rules out the formulation of a room temperature solution product with a sufficiently long shelflife for market use. Design of a stable lyophilized formulation for sterile reconstitution based on the physicochemical properties of 1 is described.

Application of liquid chromatography/mass spectrometry and nuclear magnetic resonance to the identification of degradates of a novel insulin sensitizer in aqueous solutions.

Degradation of a novel insulin sensitizer in aqueous solutions was studied using high pressure liquid chromatography/mass spectrometry (LC/MS). The insulin sensitizer, containing a thiazolidine-2,4-dione (TZD), was a new class of antidiabetic agent for the treatment of type II diabetes. Chemical stability of the insulin sensitizer was evaluated by stressing its aqueous solutions at 40 degrees C for 24 h. Oxygen was removed from one of the solutions by bubbling pure nitrogen through to identify non-oxidative pathways. LC/MS analyses of the stressed solutions revealed that hydrolysis and oxidation are the primary degradation pathways for the studied compound. A alpha-thiol acetic acid, acyl amide, and two dimeric diastereomers were the main degradates of the insulin sensitizer. The alpha-thiol acetic acid served as an intermediate-like species, and oxidized to two dimeric degradates upon exposing to air. All of them were identified as ring-opening products of the TZD. The entities of the acyl amide and dimeric degradates were respectively verified by a synthetic standard or NMR following isolation of a diastereomeric degradate. Characterization using MS in both positive and negative ion scans were discussed for an isolated diastereomeric degradate. Mechanisms of fragmentation and formation for those degradates are presented based on the MS result.