1. Nomenclature: The Isoquinoline Alkaloids, page 270, Academic Press, New York 1972.
2. and , The Alkaloids, Chemistry and Physiology, vol. XXII, ed. page 189, Academic Press, New York 1983, and references cited therein.
3. , and , J. Chem. Soc. Perkin Trans. 1, 1791 (1975).
4. Characterization of an unusual tetrahydroprotoberberine conformer by carbon-13 nuclear magnetic resonance spectroscopy