Zur Biosynthese der Alkaloide vom Rhoeadin‐Typ

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Abstract
The biosynthesis of alkaloids with 2‐phenyl‐3‐benzazepine skeleton (rhoeadine type) starts from two molecules of tyrosine. Now it was shown, using Papaver bracteatum plants, that [N‐14CH3, 8‐14C]dl‐tetrahydropalmatine methiodide (Ia) is incorporated with high efficiency into alpinigenine (III). Apparently the incorporation of the N‐quaternary salt is a specific one. A degradation sequence was applied which allows the selective determination of the radio‐activity in the non‐aromatic C‐atoms as well as the aromatic rings of alpinigenine. The incorporation of a compound with tetrahydroprotoberberine structure is in accordance with current biogenetic views. But involvement of a N‐quaternary intermediate seems quite surprising. A novel mechanism of ring rearrangement may operate. Thus, ring splitting as a step for further transformation of tetrahydropalmatine should be initiated by N‐methylation followed by hydroxylation on one of the α‐C‐atoms (C‐14 or C‐8) and subsequent hydrolysis. The significance of the feeding experiments in respect to biogenesis of benzazepine alkaloids is briefly discussed.

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