15N NMR chemical shifts in papaverine decomposition products

Papaverine can be easily oxidized to papaverinol, papaveraldine and 2,3,9,10-tetramethoxy-12-oxo-12H-indolo[2,1-a]isoquinolinium chloride. On addition of alkali solution the latter compound forms 2-(2-carboxy-4,5-dimethoxyphenyl)-6,7-dimethoxyisoquinolinium inner salt. Together with these structures the interesting 13-(3,4-dimethoxyphenyl)-2,3,8,9-tetramethoxy-6a-12a-diazadibenzo[a,g]fluorenylium chloride is discussed, which is formed in the Gadamer–Schulemann reaction of papaverine as a side product. This letter reports the 15N NMR spectra of the above mentioned compounds.

► The 15N NMR analysis of papaverine derivatives is presented. ► The chemical shifts of the nitrogen atoms are indicative for the electronic surrounding of the atoms. ► The nitrogen atoms in the uncharged structures of papaverine derivatives are pyridine-type.