Pyrrole, pyrrolidine, pyridine, piperidine and tropane alkaloids
About: This article is published in Natural Product Reports.The article was published on 2000-01-01. It has received 992 citations till now. The article focuses on the topics: Tropane & Pyrrolidine.
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TL;DR: This tutorial review summarizes the recent achievements in nucleophilic phosphine catalysis and describes how phosphines can be easily tailored to efficient annulation reactions with good control over reaction selectivity.
Abstract: Nucleophilic phosphine catalysis has proven to be a powerful tool in organic synthesis, which can provide easy access to cyclic, bicyclic or polycyclic carbocycles and heterocycles. Owing to their comparatively strong and readily tunable nucleophilicity, phosphines can be easily tailored to efficient annulation reactions with good control over reaction selectivity. This has resulted in a tremendous increase in their scope and in a concomitant number of reports where phosphine-triggered annulation reactions occur. This tutorial review summarizes the recent achievements in this area.
622 citations
TL;DR: In this paper, a Lactobacillus plantarum strain (MiLAB 393) was isolated from grass silage that produces broad-spectrum antifungal compounds, active against food-and feed-borne filamentous fungi and yeasts in a dual-culture agar plate assay.
Abstract: We have isolated a Lactobacillus plantarum strain (MiLAB 393) from grass silage that produces broad-spectrum antifungal compounds, active against food- and feed-borne filamentous fungi and yeasts in a dual-culture agar plate assay. Fusarium sporotrichioides and Aspergillus fumigatus were the most sensitive among the molds, and Kluyveromyces marxianus was the most sensitive yeast species. No inhibitory activity could be detected against the mold Penicillium roqueforti or the yeast Zygosaccharomyces bailii. An isolation procedure, employing a microtiter well spore germination bioassay, was devised to isolate active compounds from culture filtrate. Cell-free supernatant was fractionated on a C18 SPE column, and the 95% aqueous acetonitrile fraction was further separated on a preparative HPLC C18 column. Fractions active in the bioassay were then fractionated on a porous graphitic carbon column. The structures of the antifungal compounds cyclo(l-Phe-l-Pro), cyclo(l-Phe-trans-4-OH-l-Pro) and 3-phenyllactic acid (l/d isomer ratio, 9:1), were determined by nuclear magnetic resonance spectroscopy, mass spectrometry, and gas chromatography. MIC values against A. fumigatus and P. roqueforti were 20 mg ml−1 for cyclo(l-Phe-l-Pro) and 7.5 mg ml−1 for phenyllactic acid. Combinations of the antifungal compounds revealed weak synergistic effects. The production of the antifungal cyclic dipeptides cyclo(l-Phe-l-Pro) and cyclo(l-Phe-trans-4-OH-l-Pro) by lactic acid bacteria is reported here for the first time.
607 citations
TL;DR: Coupling reaction of electron-deficient aryl bromides with imidazole or pyrazole occurs at 60-90 degrees C to provide the corresponding N-aryl products in good to excellent yields and the possible action of amino acids in these coupling reactions is discussed.
Abstract: CuI-catalyzed coupling reaction of electron-deficient aryl iodides with aliphatic primary amines occurs at 40 degrees C under the promotion of N-methylglycine. Using L-proline as the promoter, coupling reaction of aryl iodides or aryl bromides with aliphatic primary amines, aliphatic cyclic secondary amines, or electron-rich primary arylamines proceeds at 60-90 degrees C; an intramolecular coupling reaction between aryl chloride and primary amine moieties gives indoline at 70 degrees C; coupling reaction of aryl iodides with indole, pyrrole, carbazole, imidazole, or pyrazole can be carried out at 75-90 degrees C; and coupling reaction of electron-deficient aryl bromides with imidazole or pyrazole occurs at 60-90 degrees C to provide the corresponding N-aryl products in good to excellent yields. In addition, N,N-dimethylglycine promotes the coupling reaction of electron-rich aryl bromides with imidazole or pyrazole to afford the corresponding N-aryl imidazoles or pyrazoles at 110 degrees C. The possible action of amino acids in these coupling reactions is discussed.
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References
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TL;DR: In this article, the turnover-limiting step in these catalytic cycles is proposed to be intramolecular insertion into the Ln−N bond of the proximal allenic CC linkage, followed by rapid protonolytic cleavage of the resulting ln−C bond.
Abstract: The total syntheses of the pyrrolidine alkaloid (+)-197B (1) and pyrrolizidine alkaloid (+)-xenovenine (2) are described. The strategy involves enantioselective syntheses of the aminoallene, (5S,8S)-5-amino-trideca-8,9-diene (3), and the aminoallene-alkene, (5S)-5-amino-pentadeca-1,8,9-triene (4), which then undergo regio- and stereoselective cyclohydroamination catalyzed by the organolanthanide precatalysts Cp‘2LnCH(TMS)2 and Me2SiCp‘ ‘(tBuN)LnN(TMS)2 (Cp‘ = η5-Me5C5; Cp‘ ‘ = η5-Me4C5; Ln = lanthanide; TMS = Me3Si). These reactive organolanthanide complexes efficiently mediate highly diastereoselective intramolecular hydroamination/cyclization (IHC) reactions under mild conditions. The turnover-limiting step in these catalytic cycles is proposed to be intramolecular insertion into the Ln−N bond of the proximal allenic CC linkage, followed by rapid protonolytic cleavage of the resulting Ln−C bond. The rate and selectivity of the insertion process is highly sensitive to the steric demands of the substrate.
243 citations
TL;DR: The α-cyanomethyloxazolidine ring system has been integrated into piperidine and pyrrolidine structures providing chiral non-racemic building blocks as mentioned in this paper.
Abstract: The α-cyanomethyloxazolidine ring system has been integrated into piperidine and pyrrolidine structures providing chiral non-racemic building blocks Reaction conditions have been determined for regio- and stereoselective substitution of the ring atoms This review highlights the applications of the methodology for the diastereoselective synthesis of both natural and unnatural derivatives containing either the piperidine or the pyrrolidine ring as a substructure
162 citations
TL;DR: In this paper, a total synthesis of the potent non-opiate analgesic alkaloid epibatidine is described, in which the key step is a reductive palladium-catalysed Heck-type coupling.
122 citations
TL;DR: Over the next three decades more than 500 alkaloids of at least two dozen structural classes were discovered, most of which have, as yet, not been found elsewhere in nature.
109 citations
TL;DR: The findings indicate that (+/-)-[3H]epibatidine specifically modulate regional nicotinic receptors in human brain and decreases significantly with age, while [3H?]nicotine binding showed no significant age-related changes in this brain region.
105 citations