South African Senecio alkaloids. Part 5. Notes on Isatidine, Rosmarinine and Pterophine, and on the structure of their necines and necic acids

20 Mar 2017

1. Isatinecine has a pyrrole nucleus and has no tertiary nitrogen atom. It must, therefore have a secondary aminogroup. The pyrrollizidine structure applicable to the two senecio bases retronecine and platynecine is, therefore, not present in isatinecine and, therefore, also not in isatidine (no tert. N-atom). 2. Isatinecine has two double bonds, the introduction of which into the pyrrollizidine molecule is not compatible with the empiric formula for isatinecine. In agreement with these properties a basic structure for isatinecine is proposed, in which the pyrrollizidine bicyclic system has opened at the point of intersection where the N-atom is situated. 3. Isatidine has one peroxygen atom which is present in the esterifying acid, isatinecic acid, which is a free peracid with one percarboxylgroup (R. CO. O. OH) which readily lactonizes. 4. The isolation of a new alkaloid pterophine is described. It has the formula C₁₈H₂₃O₅N, m.p. 227 -8°C. and [∝] 18/D = -88.5 (1.875% in CHCl₃). The alkaloid is present in both S. pterophorus and S. ilicifolius and is toxic. 5. Pterophine has a pyrrole nucleus and a tertiary N-atom which readily forms a methiodide. The nitrate and the picrate of the alkaloid have also been prepared. 6. Upon the hydrolysis of pterophine with alcoholic potash it yields the well-known senecio base retronecine and a new acid lactone (probably C₁₀H₁₆O₆). * 7. The hydrolysis with bariumhydrate of the new senecio alkaloid rosmarinine is described. The fission products are a new base rosmarinecine (C₈H₁₃O₃N) and senecic acid, C₁₀H₁₄O₄. Rosmarinine has a tertiary N-atom, which forms a methiodide and has the pyrrole nucleus. 8. Platynecic acid (the necic acid of platyphylline) is identical with senecic acid (the necic acid of senecionine and rosmarinine). 9. Besides retrorsine, S. graminifolius contains a new alkaloid, graminifoline (probably C₁₈H₂₃O₅N) in very small amounts. 10. Retrorsine is also present in S. pterophorus and S. ilicifolius.