Die Struktur des Anhydro‐isocalebassin‐methyläthers; Säurekatalysierte Umlagerungen des Curare‐Alkaloids C‐Calebassin. 60. Mitteilung über Calebassen‐Alkaloide [1]

Treatment of the Calebash alkaloid C‐calebassine ( 1 ), C 40 H 48 N 4 O 2 ++ ·2X − , with hot mineral acid yielded the anhydro‐isocalebassine acid adduct 3H , with the formula C 40 H 47 N 4 O ·3X − .H 2 O. This was converted into anhydro‐isocalebassine methyl ether salts ( 4 ) C 41 H 48 N 4 O ++ ·2X − ·H 2 O with alkaline dimethyl sulphate. A total X‐ray analysis of the orthorhombic diiodide led to formula 4 . The conversion of C‐calebassine ( 1 ) into 4 involves a radical change in the central part of the molecule. The structure of the acid adduct 3H can be deduced from the structure of 4. Treatment of 3 H with warm methanol or treatment of C‐calebassine ( 1 ) with acetic acid yielded a pale yellow compound 2 , C 40 , H 44 N 4 ++ ·2X − ·H 2 O. The central part of the molecule 2 contains a pyrrole ring, and most probably this is an intermediate in the conversion of 1 into 3 H by mineral acid. The changes of 3 H and 2 in acidic, neutral and basic media can be shown by electronic spectroscopy. Reaction of 3 H with 1 mole of oxygen at pH 4 converted it into a stable blood‐red oxidation product C 40 H 44 N 4 O 2 ++ ·2X − containing a merocyanine system. The structure 7 , proposed for this compound, is discussed.