Carbon-13 synthesis and NMR spectroscopic geometric isomer evaluation to support the filing of teriflunomide

The two isotopomers of teriflunomide were synthesized starting from isotopically stable-labeled stocks of [C-13]potassium cyanide and [1-C-13]ethyl bromoacetate. The two(13)C-labeled compounds1a, bwere applied in several NMR studies to study the E/Z ratio in different matrices. In a solution, such as dimethyl sulfoxide (DMSO), a dynamic equilibrium between E/Z-isomers (ratio of 8:92) was determined by initial(13)C-carbon NMR experiments. To get insights into the E/Z ratio of teriflunomide under in vivo conditions, advanced heteronuclear NMR (heteronuclear Overhauser effect spectroscopy [HOESY]) in D2O and mixtures of D2O/plasma were performed. Whereas NMR experiments in mixtures of water and plasma failed owing to extreme line broadening, NMR spectra in water at pH 7.4 showed only the Z-isomer.

Automated summary

The study synthesized two isotopomers of teriflunomide using isotopically labeled precursors and studied their E/Z ratio in different matrices through NMR experiments. It was found that in solution, a dynamic equilibrium between E/Z-isomers was observed. Advanced NMR techniques were used to investigate the E/Z ratio of teriflunomide under in vivo conditions, providing insights into its structural characteristics.