Left, Right, or Both? On the Configuration of the Phenanthroindolizidine Alkaloid Tylophorine from Tylophora indica

The alkaloid (-)-tylophorine was isolated from a sample of Tylophora indica, and the crude extract was analyzed by HPLC/MS(n) and chiral HPLC/MS. While the literature states that the naturally occurring form of this alkaloid is the R-enantiomer and that its S-antipode is usually not found in nature, we confirmed the hypothesis of Govindachari and Nagarajan that natural levorotatory tylophorine is indeed a nearly racemic mixture with a slight excess of the R-enantiomer.

Carbohydrates as Stereodifferentiating Auxiliaries

Carbohydrates are inexpensive natural products. Although they contain numerous functional groups and stereogenic centers in one molecule, carbohydrates were recognized as stereodifferentiating auxiliaries much later than other classes of natural products as for example amino acids or terpenes. Apart from their polyfunctional nature carbohydrates are characterized by the anomeric and exo-anomeric effects which have distinct influence of the spatial orientation of substituents linked to the anomeric position. Based on these stereochemical properties carbohydrates were used as stereodifferentiating auxiliaries in numerous diastereoselective reactions, such as aldol addition, alkylation reactio…

Synthesis of (-)-Cryptopleurine by Combining Gold(I) Catalysis with a Free Radical Cyclization (Eur. J. Org. Chem. 10/2015)

Synthesis of (-)-Cryptopleurine by Combining Gold(I) Catalysis with a Free Radical Cyclization

(R)-(–)-Cryptopleurine, a highly cytotoxic alkaloid found in Cryptocarya and Boehmeria species, was synthesized in high optical purity using a gold(I)-NHC catalyzed cyclization of an unsymmetrical phenanthrene precursor combined with a free radical cyclization to achieve closure of the C-ring.

N-[(1S,2S)-2-Amino-1,2-diphenyl­eth­yl]-4-methyl­benzene­sulfonamide [(S,S)-TsDPEN]

The crystal structure of the title compound, C21H22N2O2S, shows a network of N—H...N and N—H...O hydrogen bonds. The tolyl and 1-phenyl rings are almost mutually coplanar [7.89 (9)°], while the 2-phenyl ring makes a dihedral angle of 50.8 (1) ° with the 1-phenyl ring. An intramolecular N—H...N hydrogen bond stabilizes the molecular conformation.

Stereoselektive Synthese enantiomerenreiner Nupharamin-Alkaloide aus dem Castoreum (Bibergeil)

Tierische Parfumalkaloide: Eine stereoselektive Mannich-Michael-Reaktion an N-Galactosylfurylaldimin zu 1 (Piv = Pivaloyl), anschliesende konjugierte Cuprataddition und stereoselektive Protonierung des gebildeten Enolats, alle kontrolliert vom Kohlenhydrat, ermoglichen erstmals die Totalsynthese des all-cis-Nupharamins 2 aus dem Castoreum. Enolatprotonierung nach Abspaltung des Kohlenhydrats fuhrt alternativ zum Epimer 3.

Stereoselective Synthesis of Enantiomerically Pure Nupharamine Alkaloids from Castoreum

An animalic note: The first total synthesis of the all-cis nupharamine 2, an alkaloid from beaver castoreum, is based on the stereoselective domino Mannich-Michael reaction of N-galactosylfurylaldimine to give 1 (Piv = pivaloyl), subsequent conjugate cuprate addition, and stereoselective protonation of the enolate. These reactions are all controlled by the carbohydrate. Protonation of the enolate after cleavage of the auxiliary leads to epimer 3.

Total Synthesis of (+)-Phenguignardic Acid, a Phytotoxic Metabolite ofGuignardia bidwellii

(+)-Phenguignardic acid, a phytotoxic metabolite of the grape black rot fungus Guignardia bidwellii was synthesized, as well as its enantiomer, in eight steps from (R)-phenyllactic acid and 3-phenylprop-2-yn-1-ol. The formation of the carboxylate at a late stage, to avoid enolization of the precursor used in the central acetalization step, proved to be crucial. The synthesis of the natural product allowed the unabiguous assignment of its hitherto unknown absolute configuration.

ChemInform Abstract: Total Synthesis of (+)-Phenguignardic Acid, a Phytotoxic Metabolite of Guignardia bidwellii

(+)-Phenguignardic acid, a phytotoxic metabolite of the grape black rot fungus Guignardia bidwellii was synthesized, as well as its enantiomer, in eight steps from (R)-phenyllactic acid and 3-phenylprop-2-yn-1-ol. The formation of the carboxylate at a late stage, to avoid enolization of the precursor used in the central acetalization step, proved to be crucial. The synthesis of the natural product allowed the unabiguous assignment of its hitherto unknown absolute configuration.

Correction to: Carbohydrates as Stereodifferentiating Auxiliaries

A five-step synthesis of (±)-tylophorine via a nitrile-stabilized ammonium ylide.

The Stevens rearrangement of a nitrile-stabilized ammonium ylide is the key step of a very short and practical synthesis of the phenanthroindolizine alkaloid (±)-tylophorine. The method requires only five linear steps and is devoid of any protecting group manipulations.