Forced degradation study of thiocolchicoside: Characterization of its degradation products

Thiocolchicoside (TCC, N-[1,2-dimethoxy-10-methylsulphanyl-9-oxo-3-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydropyran-2-yloxy)-5,6,7,9-tetrahydro-benzo[a]heptalen-7-yl]-acetamide) was subjected to hydrolytic, oxidative, and photolytic stresses. TCC underwent degradation in acidic, basic, and oxidative conditions, while it was stable toward other stress conditions. The degradation products (DPs) were detected and their separation was achieved on a SGE Wakosil C18RS 5 μm (250 * 4.6 mm; SGE) column employing a gradient LC–MS method for a total time of analysis of 18 min. The mass fragmentation pathways of both thiocolchicoside and its degradation products were established using LC–MS experiments assigning the structures to the DPs. In particular, five DPs were identified as: D1SO (N-[1,2-dimethoxy-10-methylsulphoxide-9-oxo-3-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydropyran-2-yloxy)-5,6,7,9-tetrahydro-benzo[a]heptalen-7-yl]-acetamide), D1SO2 (N-[1,2-dimethoxy-10-methylsulphone-9-oxo-3-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydropyran-2-yloxy)-5,6,7,9-tetrahydro-benzo[a]heptalen-7-yl]-acetamide), D2 ([1,2-dimethoxy-10-methylsulphanyl-9-oxo-3-(3,4,5-trihydroxy-6-hydroxymethyl-tetrahydropyran-2-yloxy)-5,6,7,9-tetrahydro-benzo[a]heptalen-7-yl]-amine), D3 (N-[1,2-dimethoxy-3-hydroxy-10-methylsulphanyl-9-oxo-5,6,7,9-tetrahydro-benzo[a]heptalen-7-yl]-acetamide or 3-O-demethylthiocolchicine), D4 ([1,2-dimethoxy-3-hydroxy-10-methylsulphanyl-9-oxo-5,6,7,9-tetrahydro-benzo[a]heptalen-7-yl]-amine or N-deacetyl-3-O-demethylthiocochicine). Moreover, the structures of DPs were confirmed by synthesis of the reference standards which were fully characterized by MS, NMR, IR analyses. Finally a comprehensive degradation scheme of TCC was proposed allowing to outline D1SO and D3 as the indicators of its stability for oxidative and hydrolytic stress conditions.

► Hydrolytic, oxidative, and photolytic stresses of thiocolchicoside (TCC).
► Degradation products were detected and characterized using LC–MSn experiments.
► Five DPs were identified and confirmed by synthesis, MS, NMR and IR analyses.
► A comprehensive degradation scheme of TCC was proposed.
► D1SO and D3 are the indicators of TCC stability for oxidative and hydrolytic stress.