The natural alkaloid lappaconitine, the anthranilic acid ester, is used against arrhythmias in medical practice, but it undergoes significant photodegradation. The latter may be the cause of the drugs phototoxicity. Furthermore, other esters of anthranilic acid are also widely used in practice, for example, as UV filters; so their photostability is an important characteristic. Thus, the improvement of these compounds resistance against light irradiation is the issue of the day. This work has shown that the appending of a substituent through the acetylene bridge into the anthranilic acid aromatic ring can significantly decrease the lappaconine derivatives photodegradation degree. The photodegradation process, according to the chemically induced dynamic nuclear polarization (CIDNP) analysis, begins with intramolecular or intermolecular reversible electron transfer (ET) with subsequent cleavage of the ester bond. The main product of the photolysis is the quaternary ammonium salt of 20-ethyl-1-α,14-α,16-β-trimethoxyaconitane-4,8,9-triol (lappaconine) of substituted anthranilic acid. It was demonstrated that the photodegradation of the lappaconitine acetylenic derivatives occurs from their triplet excited states and the substitution influences primarily the triplet reactive state formation effectivity.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics