Synthesis and structure elucidation of a new isoquinolinium inner salt

Papaverine is a drug that can be easily oxidized to papaverinol, papaveraldine and to recently discovered 2,3,9,10-tetramethoxy-12-oxo-12H-indolo[2,1-a]isoquinolinium chloride. In a strong alkaline medium the spectroscopic properties of this latter compound are modified indicating formation of a new compound. The isolation and structure elucidation of this compound as 2-(2-carboxy-4,5-dimethoxyphenyl)-6,7-dimethoxyisoquinolinium inner salt are reported.