Download PDF by Raymond K.N. (ed.): Bioinorganic Chemistry II

By Raymond K.N. (ed.)

ISBN-10: 0841203598

ISBN-13: 9780841203594

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The structure (46) has also been confirmed by independent total synthesis, using generally the same methods as given above for the synthesis of 3,4-dihydropapaverine, the methochloride of which (47) on reduction affords laudanosine. The products of Hofmann degradation of laudanosine are thus seen to have the structures (48, R = Me) and (49), and it is of interest that the pyrolysis of laudanosine TV-oxide involves degrada­ tion to the hydroxylamine (48, R = OM), since the exocyclic /3-carbon bears a hydrogen that can participate in the cyclic transition state (50).

Exhaustive methylation requires two steps for removal of the nitrogen, which then appears as trimethylamine and accord­ ingly the nitrogen atom must be part of a single ring. The nitrogenfree product of exhaustive methylation C 1 9 H 1 8 0 4 contains two reducible double bonds and two benzene rings, and can be oxidised to a tricarboxylic aromatic acid C 18 H 16 O 10 indicating that the ether oxygen must join the two aromatic nuclei. The production of a tricarboxylic acid rather than a mono or dicarboxylic acid in the final oxidation indicates also that in the nitrogen-free product the aromatic nuclei are also joined by an olefinic system.

Exhaustive methylation of dauricine methyl ether and oxidation of the nitro­ gen free product gave ra-hemipinic acid (18) and the dicarboxylic acid (15, R = Me), suggesting the structure (17, R = Me) for the alkaloid methyl ether, which was confirmed by synthesis of the methine base (19) by Hofmann degradation of the base (20) obtained by a laudanosine-type synthesis from homoveratrylamine (21) and the dicarboxylic acid (22). (19) The position of the phenolic group in dauricine is indicated by the exhaustive methylation of the ethyl ether to an TV-free product oxidisable to the acid (15, R = Et) obtained from magnoline triethyl ether.

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Bioinorganic Chemistry II by Raymond K.N. (ed.)

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