Mesembrane alkaloids

A detailed account concerning the isolation and characterization of the pyrido-mesembran alkaloids A4(7) and iV-formyltortuosamine (8) and the mesembran bases (9 R = H, R = OMe), (10), and (9 R = R = H) from Sceletium namaquense and S. strictum has appeared. Their structures were established by detailed H and... 

Mori et al. have shown that asymmetric alkylation with an allylic tosyl amide followed by a zirconium-promoted cyclization provides an efficient route to mesembrine and mesembrane alkaloids [107]. The best ee was obtained with BINAPO as the ligand. Scheme 28. The product was obtained in 86% ee and following recrystallization the sulfonamide was obtained in 99% ee. 

C. Botteghi, L. Lardicci and R. Menicagli, Optically active Heteroaromatic Compounds VI 3-substituted Furans and Thiophenes from a(,B-unsaturated Aldehydes, J. Org. Chem. 38 (1973) 2361-1365 C.P. Forbes, W.J. Schoeman, H.F. Strauss,E.M.M. Venter and A. Wiechers, Applications of substituted Aryl Acetaldehydes in the Total Synthesis of seco-Mesembrane Alkaloids Part I. The Total Synthesis of 1-0-Methyljoubertiamine, J. Chem.Soc. Perkin I 1980, 906-910. 

The mesembrane alkaloid (-)-mesembranone has been synthesized using a neat application of the amide acetal Claisen rearrangement (Scheme 82)/ ... 

Although the alkaloids of the mesembrane type are structurally similar to certain alkaloids of the family Amaryllidaceae, they are generally found in the plants of the family Aizoaceae, but there have been several exceptions to this generalization. For example, amisine (580) has been isolated from Hymenocallis arenicola Northrop (57), and mesembrenol (581) has been isolated from Crinum oliganthum (41). The isolation of 580 and 581 represented the first instances in... 

Sceletium Alkaloids.—(-)-Mesembrane has been isolated from S. namaquense L. Bolus X-ray diffraction analysis of its hydrochloride monohydrate revealed its relative and absolute configuration (10). (-)-Mesembrine has the absolute configuration (11), in accord with (10), and it is now firmly established that alkaloids of this family belong to a single antipodal series.13... 

The mesembrine alkaloids, a group of alkaloids named after the most important representative, mesembrine, have been studied in detail only recently. The basic skeleton of these alkaloids is formed by mesembrane (I), an A -methyl-3a-(3, 4 -dimethoxyphenyl)-d5-octahydroindole. The mesembrine alkaloids are closely related to the 5,10b-ethanophenan-thridine group of the Amaryllidaceae alkaloids which are derived from crinane (II). 

Recent indications point to the fact that the mesembrine alkaloids constitute a larger group than previously envisaged and for this reason it has been proposed that the mesembrane skeleton (26 = H) be used as a basis for nomen-... 

Synthetic work on the mesembrane group will no doubt be further stimulated by reports on their central nervous system activity and somewhat surprising biosynthesis. An interesting asymmetric synthesis of unnatural (+ )-mesembrine (38) has been announced (Scheme 4). The key intermediate (35), prepared in nine steps from 1,2-dimethoxybenzene, was treated with L-proline pyrrolidide (36) under conditions typical for the preparation of enamines. The product was not isolated but subjected to reaction with methyl vinyl ketone followed by acid treatment to give the cyclohexenone (37) in 38 % overall yield. The last step in the synthesis [(37) — (38)] was based on previous synthetic work on mesembrine alkaloids. The synthetic (+ )-mesembrine (38) was shown to exhibit a positive Cotton effect and thus an antipodal relationship to natural (— )-mesembrine. The mesembrine analogues (40 = H or OMe, = H, Me, or CHjPh) have... 

Almost all of the lycorine-type alkaloids isolated from Narcissus present a trans-rmion between B/C rings, making them especially vulnerable to oxidative processes. It is interesting to observe that four of these alkaloids, namely vasconine (22), tortuosine (23), ungeremine (24), and roserine (25) possess an unusual quaternary nitrogen (67 71). The species N. pallidulus (section Ganymedes), unusual because it contains mesembrane-type alkaloids, is even more exceptional due to the presence of roserine. 

Asymmetric substitution sodium salt Synthesis of mesembrane and mesembrine Synthesis of amaryllidaceae alkaloids Remote asymmetric induction... 

D.i.a. Synthesis of Natural Products by Allylation of the Cyclohexenyl Moiety. Many alkaloids have a di-3a-aryloctahydroindole skeleton like mesembrane, mesembrine, or crinane-type alkaloids (Scheme 44). They have been of interest as synthetic targets due to the wide range of biological activities they exhibit. 

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