Indolizidines stereochemistry

Dieckmann reaction, 4, 471 Indolizidine alkaloids mass spectra, 4, 444 Indolizidine immonium salts reactions, 4, 462 Indolizi dines basicity, 4, 461 circular dichroism, 4, 450 dipole moments, 4, 450 IR spectra, 4, 449 reactivity, 4, 461 reviews, 4, 444 stereochemistry, 4, 444 synthesis, 4, 471-476 Indolizine, 1-acetoxy-synthesis, 4, 466 Indolizine, 8-acetoxy-hydrolysis, 4, 452 synthesis, 4, 466 Indolizine, I-acetyl-2-methyI-iodination, 4, 457 Indolizine, 3-acyloxy-cyclazine synthesis from, 4, 460 Indolizine, alkyl-UV spectra, 4, 449 Indolizine, amino-instability, 4, 455 synthesis, 4, 121 tautomerism, 4, 200, 452 Indolizine, 1-amino-tautomerism, 4, 38 Indolizine, 3-amino-synthesis, 4, 461, 470... 

Among the many recent applications to natural products, syntheses of pyrrolizidine and indolizidine alkaloids that take advantage of the 1,3-dipolar cycloaddition methodology have been reviewed [8]. The regio- and stereochemistry [9] as well as synthetic appHcations [10] of nitrile oxide cycloadditions have also been discussed. 

The product of the reaction in Entry 8 was used in the synthesis of the alkaloid pseudotropine. The proper stereochemical orientation of the hydroxy group is determined by the structure of the oxazoline ring formed in the cycloaddition. Entry 9 portrays the early stages of synthesis of the biologically important molecule biotin. The reaction in Entry 10 was used to establish the carbocyclic skeleton and stereochemistry of a group of toxic indolizidine alkaloids found in dart poisons from frogs. Entry 11 involves generation of a nitrile oxide. Three other stereoisomers are possible. The observed isomer corresponds to approach from the less hindered convex face of the molecule. 

Swainsonine is a trihydroxylated bicyclic indolizidine alkaloid with four chiral centres, whose relative stereochemistry was determined by X-ray crystallographic analysis and the absolute configuration was deduced on the basis of biosynthetic and asymmetric induction studies, and then confirmed by an enantiospecific synthesis from D-mannose [2a]. 

Iminium ion-vinylsilane cyclizations closely related to the one described here have been used to prepare indolizidine alkaloids of the pumiliotoxin A and elaeokanine families, indole alkaloids, amaryllidaceae alkaloids, and the antibiotic (+)-streptazolin. The ability of the silicon substituent to control the position, and in some cases stereochemistry, of the unsaturation in the product heterocycle was a key feature of each of these syntheses. 

In order to assign the stereochemistry of the isomers, indolizidine preparations from 2,6-lutidine (351) by Sonnet (134,435) were employed. The hy-droxyalkylpyridine (392) obtained from 351 was catalytically reduced to afford... 

The stereochemistry of indolizidine and pyrrolizidine metho salts was studied by Meyer and Sapianchiay.289 They found that methylation of indolizidine gave a 50 50 mixture of isomers from which only the cis-metho salt could be obtained pure. Cyclization of either 250 or 251 gave only the cis isomer, which can be accounted for on the basis of less... 

The 5,8-disubstituted indolizidines and 1,4-disubstituted quinolizidines are the more common structural patterns found in amphibian skin[21]. None of these alkaloids has so far been reported from any other source. In addition, the biological activity of only a few 5,8-disubstituted indolizidines has been investigated due to the isolation in minute quantities from the skin. Among them, the relative stereochemistry of quinolizidine 2071 was anticipated to be 75 by our chiral synthesis of 76[35] followed by stereocontrolled synthesis of 75[36]. A sample of synthetic racemate of 75 had produced the best separations on GC analysis with (3-dextrin chiral column[36]. 

Advances in the Study of the Stereochemistry of Quinolizidines, Indolizidines and Pyr-rolizidines I. M. Skvortsov, Russ. Chem. Rev. (Engl. Transl), 1949, 48, 262-281. 

D NMR studies of stellattamide B allowed the identification of the indolizidine nucleus and of the side chain structure. The relative configuration of the indolizidine nucleus was established by NOESY connectivities and the absolute stereochemistry of the 13 -methyl group was determined via chemical oxidation of the side chain to (S)-2-methylglutaric acid. The nature of the counterion was determined by energy-dispersive spectroscopic experiments. 

M. Vemura et al., ibid., p.4369), although the stereochemistry of the indolizidine unit remained uncertain for some time. 

Solanopubamine, from the aerial parts of 5. pubesaens, has been investigated spectroscopically. It is isomeric with solanogantamine (62) and since its structure and stereochemistry have been settled (64) it follows that the C-25 methyl group in solanogantamine must be 3 (Kaneko et al., Phytochem., 1985, 1369). The indolizidine group... 

All the currently known indolizidine and quinolizidine alkaloids isolated from ants are illustrated in Fig. 6. (+ )-Monomorine I (427), the well-studied trail pheromone constituent of the Pharaoh ant Monomorium pharaonis), and the analogs 428-431 were described in the earlier volumes in this series. These five compounds are 3,5-disubstituted indolizidines bearing short saturated or mono-unsaturated hydrocarbon chains. The relative stereochemistry in monomorine VI (430) still remains unknown, while that of 431 was atypical for the class at the time of its isolation 380). The structural resemblance of fiiis group of alkaloids to the... 

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