Lophocerine, biosynthesis

The apparent use of an aldehyde function to form the junction of the C5 unit with phenethylamine fragment in lophocerine biosynthesis makes an interesting contrast with the biosynthesis of the related alkaloids anhalamine (65) and anhalonidine (66), where the a-carbonyl acids, glyoxylic acid and pyruvic acid respectively, are very evidently intermediates. The analogous keto-acid for lophocerine is (64), simply... 

The number of alkaloids based on the 1-substituted tetrahydroisoquinoline skeleton is legion and the structural variation which this skeleton affords, particularly in the case of 1-benzylisoquinolines, is rich. The 1-substituted isoquinoline skeleton of each kind probably arises by the common step of condensing a j8-arylethylamine with an appropriate carbonyl compound, for which the Pictet-Spengler reaction provides an analogy. In some cases the participation of a carbonyl compound is established but in others it is still speculative. Recently progress has been made in this area in studies on the biosynthesis of lophocerine, the Papaver alkaloids, and to some extent the cryptostyline alkaloids with their novel 1-phenylisoquinoline structures. 

O Donovan DG, Barry E (1974) Biosynthesis of lophocerine in Lophocereus schottii, part II. J Chem Soc Perkin Trans 1. 2528-2529... 

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