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Abstract 9‐Methoxytetrahydroprotoberberines are found to exhibit pronounced ( M OCH 3 ) + ions in their mass spectra as opposed to isomers or homologs lacking such substitution, yet carrying methoxyl substituents at other sites. Locating such substituents originally present, or produced from 9‐hydroxy groups by treatment with diazomethane, allows to differentiate 9, 10‐ from 10, 11‐oxygenation patterns in ring D , and thus to secure an important step in the structure elucidation of unknown alkaloids of this class.
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Richter et al. (1975) studied this question.
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