Two Atropisomeric N-Methyldioncophyllines A and N-Methylphylline, their Naphthalene-Free Heterocyclic Moiety, from Ancistrocladus barteri

The West African plant Ancistrocladus barteri (Ancistrocladaceae) was investigated chemically for the first time. Besides the known naphthylisoquinoline alkaloids N-methyldioncophylline A and 7-epi-N-methyldioncophylline A (i.e. its atropo-diastereomer), a new naphthalene-free alkaloid, belonging to the ‘Dioncophyllaceae type’, was isolated. Its structure was elucidated by spectroscopic and degradative methods and confirmed by total synthesis. The new compound, named N-methylphylline, is exactly the isoquinoline “half” of both, N-methyldioncophylline A and its atropisomer. Furthermore, the related tetrahydroisoquinoline O,N-dimethylphylline, an intermediate in the chemical synthesis of N-methylphylline, was detected as a new natural product in crude extracts of A. barteri.