The clinical efficacy of chemotherapy against rapidly proliferating cells stimulates both the development of new agents and the reassessment of established drugs. Spectroscopic methods (UV, FT-IR, and 1H NMR) were applied to characterize prospidium chloride and related substances. The FT-IR spectrum of prospidium chloride, arising from vibrational transitions within the alkyl fragments of the dispirotripiperazinium cation, is reported with band assignments. Electronic transitions between molecular orbitals are analyzed using quantum–mechanical selection rules (Laporte and spin selection rules). The n→σ* transition (ΔS = 0) corresponds to the absorption maximum at λmax = 282 ± 0.40 nm (ε = 3.89 ± 0.08 L·mol−1·cm−1). A 1H NMR spectrum (700 MHz) was used to assign chemical shifts δ (ppm), J-coupling constants (Hz), and gauche conformational features of prospidium chloride and its dihydroxy and epoxy impurities. Quantitative 1H NMR (qNMR) was applied to determine the content of the active pharmaceutical ingredient and related substances. The methods provide complementary structural information for the characterization of prospidium chloride.
Kladiev et al. (Thu,) studied this question.