Chemical characterization of the degradation products of vinblastine dihydrogen sulfate

Vinblastine was incubated in 0.2 M glycine buffer (pH 7.4 or 8.8) containing bovine serum albumin (1%) at 37 degrees C for 72 h. The reaction mixture was extracted with CH2Cl2, and the extract gave 6 major peaks (A, B, C, D, E, and F) with retention times of 5.0, 7.5, 11.0, 13.0, 23.0, and 30.0 min, respectively, in a high-performance liquid chromatography system (muBondapak C18 column; solvent, 50% MeOH in 10 mM KH2PO4, pH 4.5; flow rate, 1.2 ml/min; detector, 254 nm). Vinblastine in this system corresponded with peak C, and its spectral data were identical to those of the parent compound. The UV, infrared, and mass spectral properties of these peaks were as follows [UV (lambda max); infrared (cm-1); mass spectrum (m/z)]: peak A: 214, 266, and 315 nm; 3464, 2850, and 1730; and 769 (MH+); peak B: 213, 258, 285, and 295 nm; 3457, 2951, 2580, and 1734; and 809 (MH+); peak C: 214, 266, 292, and 312 nm; 3457, 2951, and 1734; and 811 (MH+); peak D: 212, 266, 285, and 312 nm; 3467, 2915, and 1734; and 811 (MH+); peak E: 212, 260, 285, 294, and 313 nm; 3479, 2850, and 1734; and 825 (MH+); and peak F: 212, 265, 283, and 312 nm; 3407, 2857, and 1734; and 807 (MH+). These data suggest the following tentative structures for the degradation products: peak A, 4-deacetylvinblastine; peak B, 19'-hydroxy-3',4'-dehydrovinblastine; peak D, an isomer of vinblastine; peak E, 19'-oxovinblastine; and peak F, 3',4'-dehydro-19'-oxovinblastine. The structure of peak A as 4-deacetylvinblastine was further confirmed by chemical synthesis.