Die Struktur des mesembrins und Mesembrenins

Popelak, A.; Lettenbauer, G.; Haack, E.; Spingler, H.

doi:10.1007/bf00602769

Cited by 26 publications

(4 citation statements)

References 2 publications

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“…An analytically pure sample of the synthetic material was obtained after bulb-to-bulb distillation under reduced pressure (0.01 Torr/160 °C). The optical rotation of the synthetic product, [α] D = −63.3° (MeOH, c = 1.13), was in close agreement with values reported in the literature for natural mesembrine, [α] D = −55.4°, −59° (MeOH). , Spectral data, including 1 H NMR, 13 C NMR, and IR, were collected for both the natural and synthetic samples and found to be in full agreement…”

Section: Resultssupporting

confidence: 85%

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Asymmetric Construction of a Quaternary Carbon Center by Tandem [4 + 2]/[3 + 2] Cycloaddition of a Nitroalkene. The Total Synthesis of (−)-Mesembrine

Denmark

Marcin

1997

J. Org. Chem.

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An efficient, total synthesis of the Sceletium alkaloid (-)-mesembrine is accomplished in seven steps and 19% yield from a functionalized nitroalkene (itself prepared in six steps and 34% yield from ethyl 3-bromopropionate). The construction of the octahydroindole framework of mesembrine features a tandem inter [4 + 2]/intra [3 + 2] cycloaddition of a 2,2-disubstituted 1-nitroalkene and a chiral vinyl ether derived from (1R,2S)-2-(1-methyl-1-phenylethyl)cyclohexanol as the central strategic element. The two stereogenic centers of the natural product, which include a benzylic, quaternary center, were established in 26/1 selectivity in the tandem process. Scheme 2 Scheme 3Total Synthesis of (-)-Mesembrine

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Section: Resultssupporting

confidence: 85%

“…5a Structural investigations began in 1957, when it was revealed that mesembrine contains a ketone, a tertiary amine, and two methoxy substituents . In 1960 the complete structure was elucidated by Popelak and co-workers through a combination of degradation and synthetic methods …”

Section: Introductionmentioning

confidence: 99%

Asymmetric Construction of a Quaternary Carbon Center by Tandem [4 + 2]/[3 + 2] Cycloaddition of a Nitroalkene. The Total Synthesis of (−)-Mesembrine

Denmark

Marcin

1997

J. Org. Chem.

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“…Tropane alkaloids already are found sporadically in many families of dicot plants distinct from Solanaceae and Convolvulaceae, e.g., in Proteaceae, Brassicaceae, and Rhizophoraceae (Lounasmaa and Tamminen, 1993). Examples for further alkaloids containing the N -methylpyrroline moiety are numerous in plants, e.g., hygrine and shihunine in Dendrobium species (Orchidaceae, a monocot) (Luening and Leander, 1965; Leete and Bodem, 1976) or mesembrine and mesembrinine in Sceletium species (Aizoaceae, Caryophyllales) (Popelak et al, 1960). The frequent occurrence of putative N -methylputrescine derivatives and the few mutations that are needed to generate PMT activity in SPDS proteins leads us to speculations.…”

Section: Discussionmentioning

confidence: 99%

Evolution of the key alkaloid enzyme putrescine N-methyltransferase from spermidine synthase

Junker¹,

Fischer²,

Sichhart³

et al. 2013

Front. Plant Sci.

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Putrescine N-methyltransferases (PMTs) are the first specific enzymes of the biosynthesis of nicotine and tropane alkaloids. PMTs transfer a methyl group onto the diamine putrescine from S-adenosyl-l-methionine (SAM) as coenzyme. PMT proteins have presumably evolved from spermidine synthases (SPDSs), which are ubiquitous enzymes of polyamine metabolism. SPDSs use decarboxylated SAM as coenzyme to transfer an aminopropyl group onto putrescine. In an attempt to identify possible and necessary steps in the evolution of PMT from SPDS, homology based modeling of Datura stramonium SPDS1 and PMT was employed to gain deeper insight in the preferred binding positions and conformations of the substrate and the alternative coenzymes. Based on predictions of amino acids responsible for the change of enzyme specificities, sites of mutagenesis were derived. PMT activity was generated in D. stramonium SPDS1 after few amino acid exchanges. Concordantly, Arabidopsis thaliana SPDS1 was mutated and yielded enzymes with both, PMT and SPDS activities. Kinetic parameters were measured for enzymatic characterization. The switch from aminopropyl to methyl transfer depends on conformational changes of the methionine part of the coenzyme in the binding cavity of the enzyme. The rapid generation of PMT activity in SPDS proteins and the wide-spread occurrence of putative products of N-methylputrescine suggest that PMT activity is present frequently in the plant kingdom.

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“…This plant is also known as kanna and has been used as a stimulant by South African natives . In 1957, Bodendorf and Krieger published the first accurate structural elucidation of mesembrine, and three years later Popelak et al determined its absolute configuration (Figure ).…”

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confidence: 99%