Determination of the Degradation Chemistry of the Antitumor Agent Pemetrexed Disodium.
Stress-testing (forced degradation) studies have been conducted on pemetrexed disodium heptahydrate (1) (LY231514·2Na·7H2O) drug substance in order to identify its likely degradation products and establish its degradation pathways. Solid samples of the drug substance were stressed under various conditions of heat, humidity, and light, and solutions of the drug substance were stressed under various conditions of heat, light, oxidation, and over a wide pH range (1-13). The stressed samples were analyzed using a gradient elution reversed-phase HPLC method. The 7 major degradation products detected in the stress-testing studies were isolated, and the structures were elucidated via spectroscopic characterization. The structures of the degradation products and their proposed mechanisms of formation indicate that 1 degrades via 2 main pathways: oxidation and hydrolysis. Of the 7 identified degradation products, 6 are proposed to result from oxidation and 1 from hydrolysis.
Pemetrexed degradation by photocatalytic process: Kinetics, identification of transformation products and estimation of toxicity.
This study employed a UV-A/visible/TiO2 system to investigate the degradation of pemetrexed, an antifolate agent used in chemotherapy. The laboratory-scale method employed a photostability chamber that could be used to study multiple samples. Reversed-phase HPLC coupled with high-resolution ESI-LTQ-Orbitrap mass spectrometry was used to determine the transformation products (TPs) of PEME. Based on the identified TPs and existing chemical knowledge, the mechanism of degradation of the target compound was proposed. Concentrations were monitored as a function of time, and the degradation kinetics were compared. The structures of seven TPs, four of which have not been described to date, were proposed. Most of the TPs stemmed from OH radical additions to the dihydropyrrole moiety and oxidative decarboxylation of the glutamate residue. Based on the elucidated structures, a computational toxicity assessment was performed, showing that the TPs with higher log D values than the parent compound are more toxic than the PEME itself. To support these findings, the toxicities of irradiated samples on Vibrio fischeri were monitored over time. The experimental results corresponded well with the results of previous computational studies.
The degradation of the antitumor agent gemcitabine hydrochloride in an acidic aqueous solution at pH 3.2 and identification of degradation products.
A study of the degradation kinetics of gemcitabine hydrochloride (2'-deoxy-2',2'-difluorocytidine) in aqueous solution at pH 3.2 was conducted. The degradation of gemcitabine followed pseudo first-order kinetics, and rate constants were determined at four different temperatures. These rates were used to construct an Arrhenius plot from which degradation rates at lower temperatures were extrapolated and activation energy calculated. Four major degradation products were identified. Only one of these degradation products, the uridine analogue of gemcitabine, was a known degradation product of gemcitabine and was identified by comparison with synthesized material. The other three degradation products were isolated and characterized by spectroscopic techniques. Two of these products were determined to be the diastereomeric 6-hydroxy-5, 6-dihydro-2'-deoxy-2',2'-difluorouridines, and the other product was determined to be O(6),5'-cyclo-5,6-dihydro-2'-deoxy-2', 2'-difluorouridine. The mechanisms of formation of these degradation products are discussed.