Lythraceae alkaloids. VII. Structure and stereochemistry of the biphenyl alkaloids of Decodon and Hemia

The biosynthesis of the Lythraceae alkaloids. II. The phenylalanine-derived fragments

“…Alkaloids with trnt~s-ringjunction cis-ring junction e.g., decodine (5) and e.g., vertine (25) and decinine (6) decamine ( found in cryogenine (25) in H. salicifolia (3,26). The distribution of label in the alkaloids obtained in experiment 12 is entirely different.…”

“…The carbonyl carbon atom of the lactone ring (C-11) of each of the two alkaloids was obtained by phenylation of dimethyldecodine (7) and methyldecinine (17), respectively, with phenyl Grignard reagent (29). The diphenylcarbinols so obtained were dehydrated to the diphenylolefins (11) and (19), respectively, and these were subjected to chromic acid oxidation, yielding C-1 1 as benzophenone, which was isolated as the oxime.…”

“…Such a model is shown in Scheme 6. It invokes intermediacy of a 2-substituted piperidine (29), analogous in structure to the Decodon intermediate 27, and of a 2,6-disubstituted piperidine (30). The latter is analogous in structure (33) …”

“…Several biogenetic proposals (1-4) have been advanced to account for the origin of the phenylquinolizidine lactone alkaloids (e.g., decodine (5) and decinine (6)) found in several genera of the family Lythraceae (e.g., Decodon verticillatus (5, 6), Heimia salicifolia and H. myrtifolia (7-1 l), Lagerstroetnia indica (12), and Lytlrrum lanceolatum (13)) (Scheme 1). Steps common to all the proposals are the reduction of a phenylquinolizidinone (1, or the corresponding cis-ring-fused isomer) to the corresponding phenylquinolizidinol (2), followed by insertion into the latter, by ester formation and phenol coupling, of a phenylpropanoid (C6-C,) unit (e.g., p-coumaric acid (3)) derived from phenylalanine via cinnamic acid.…”

“…The first paper of this series (25) dealt with the status of lysine and its metabolites in the biosynthesis of decodine (5) and decinine (6), phenylquinolizidine lactone alkaloids from Decodon uerticillatus. In the present investigation, the question is examined whether it is a C6-C, unit, or a C6-C, unit, derived from phenylalanine, which is implicated in the biosynthesis of the phenylquinolizidinol system of the Decodon alkaloids.…”