1-Methyl-6-Ethyl-3-Azaphenanthrene, a Key Degradation Product of Atisine

The Diterpene Alkaloids. Further Studies of Atisine Chemistry1

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A functional group analysis of atisine (1), isoatisine (4), and dihydroatisine (2) by infrared spectroscopy, Kuhn-Roth oxidation, and ozonolysis indicates the presence of hydroxyl, CCHz, and exocyclic methylene groups in each compound. The existence of an oxazolidine ring in atisine is demonstrated by oxidation to a lactam dicarboxylic acid (6) whose dimethyl ester (7) shows no hydroxyl absorption in the infrared. Oxidation of atisine and isoatisine with chromium trioxide-pyridine gave enones 10 and 11, respectively, which showed the absence of hydroxyl absorption in the infrared.

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“…In the course of our continuing studies on atisine, the major diterpene alkaloid3 of Aconitum heterophyllum Wall (Ranunculaceae), we have found it expedient from time to time to present our work describing the elucidation of certain structural features of atisine in the form of preliminary communications. [4][5][6][7][8][9][10][11][12][13] Now that this work and that from other labora-tories14-18 have culminated in the assignment of the complete structure and stereochemistry to this compound, we wish to disclose the details of our work and to discuss certain interesting chemical features of the atisine molecule. This chemistry will be discussed in terms of structure 1 which has recently been confirmed by two independent total syntheses.…”

“…Direct proof for the existence of an oxazolidine ring in atisine and isoatisine was provided by two lines of evidence. 4 (1) Oxidation of atisine with potassium permanganate in acetone gives a lactam dicarboxylic acid (6).25-27,31 Examination of the infrared spectrum of the dimethyl ester (7) reveals bands at 1731 (broad, -C02CH3) and 1642 cm.-1 ( -lactam), but no band indicative of a hydroxyl group. The Tschugaeff-Zerewitinoff determination was negative on the diester 7 but showed one active hydrogen for atisine (1).…”

“…spectrum of the imino alcohol 12 showed the presence of CCift ( 9.18, 3H, singlet), CJT^N=C (r 6.60, 2H, doublet, J = 2.5 c.p.s. ), and -N=Gff-(r 2.13, 1H, broad signal, half-band width, 7 c.p.s.) groups.…”

Diterpenoids

“…On mild alkaline treatment of atisine, a molecular rearrangement to isoatisine takes place. Dehydrogenation of atisine with selenium yielded a hydrocarbon, 6-ethyl-1-methylphenanthrene (82) and a Ci6Hi6N base, for which structure LXXV was rigidly established by synthesis (100).…”