title: Degradation of paclitaxel and related compounds in aqueous solutions III: Degradation under acidic pH conditions and overall kinetics.
abstract: Paclitaxel and related taxanes are complex molecules with numerous hydrolysable ester groups, possible epimerization at the 7-position, and possessing a strained oxetane ring, a possible site for acid-catalyzed cleavage. Presented here is the stability of paclitaxel, 10-deacetylbaccatin III, baccatin III, and N-benzoyl-3-phenylisoserine ethyl ester in aqueous solution over a pH range of 1-5 at various temperatures. Analysis of various samples was by HPLC-UV and LC-MS. Baccatin III, 10-deacetylbaccatin III, and N-benzoyl-3-phenylisoserine ethyl ester were found to undergo acid catalysis since pH-rate profiles all followed a first-order dependency in hydrogen ion concentration. No evidence of any epimerization was noted at acidic pH values. Baccatin III and 10-deacetylbaccatin III showed similar degradation rates with possible products being possible dehydration around the 13-hydroxy group and cleavage of the oxetane ring. Cleavage of the 10-acetyl group of baccatin III was a minor initial pathway. N-Benzoyl-3-phenylisoserine ethyl ester degraded significantly slower than both 10-deacetylbaccatin III and baccatin III. At pH 2, paclitaxel degraded at a rate between that of N-benzoyl-3-phenylisoserine ethyl ester and 10-deacetylbaccatin III. The pH of maximum stability for all compounds appeared to be around pH 4.
authors.affiliation: Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, Kansas 66047, USA.
authors.forename: Jiaher
authors.initials: J
authors.lastname: Tian
authors.forename: Valentino J
authors.initials: VJ
authors.lastname: Stella
mesh_terms: D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D017239:Paclitaxel / Q000031:analogs & derivatives / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D043823:Taxoids / Q000737:chemistry; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D043823:Taxoids; D014867:Water; D017239:Paclitaxel