Structural Elucidation, Chemical Reaction, and Stereochemistry of Phenethylisoquinoline Alkaloids

Structural Elucidation, Chemical Reaction, and Stereochemistry of Phenethylisoquinoline Alkaloids 

Of the simple phenethylisoquinoline alkaloids dysoxyline (8), (5)-(-t-)-homolaudanosine (9), and (-)-isoautumnaline (10), 8 and 9 were isolated from Dysoxylum lenticellare Gillespie (5). Alkaloid 10 was isolated from Colchicum ritchii R.B. (4). 

Alkaloids 8 and 9 were identified as simple 1-phenethylisoquinolines by means of their mass spectra. The parent ions of 8, mlz 355 (C21H25NO4), and 9 mlz 371 (C22H24NO4), differ by 16. Both compounds show a base peak at mlz 206 resulting from the loss of a phenethyl radical from the parent ion. A similar loss of the C-1 benzyl radical produces the base peak 

The H-NMR spectra are in full agreement with structures 8 and 9. The circular dichroism (CD) spectra obtained from 8 and 9 each showed positive Cotton effects near 280 and 240 nm. Since the CD spectrum of 

The diphenolic isoquinoline (10), C21H27NO5, was obtained together with the known isomeric base (-)-autumnaline (11). The H-NMR spectrum of 10 differed from that of 11 only by a slight shift of the H-5 and H-8 absorptions. This indicated that the isomerism resided in ring A, more specifically in the relative positions of the methoxy and hydroxy substituents. Complete NOE studies of 10 and 11 conclusively established the substitution pattern in rings A and C in each case (4). 

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