Aromatic motifs in the design of Ephedra ligands for application in the asymmetric addition of diethylzinc to aldehydes and diphenylphosphinoylimines

Enantiomer separation of 2-halomandelic acids via diastereomeric salt formation with chiral N-substituted 2-amino-2-phenylethanols

Chiral N-substituted secondary 1,2-aminoalcohols have been developed for the enantioseparation of ortho-halomandelic acids (o-X-MAs) via diastereomeric salt formation. Two structural isomers, N-methyl-2-amino-1,2-diphenylethanol and N-benzyl-2-amino-2-phenylethanol, showed high separation abilities for o-X-MAs (X = Cl, Br, I). The chiral recognition mechanism was elucidated by crystallographic analysis of the less-soluble salts. The substituents on the nitrogen atom of the resolving agents and the inclusion of the crystallization solvent stabilized the salt and enhanced their separation ability.

Preparation and Asymmetric Induction Evaluation of the First Ephedrine-Based Ligands Immobilized on Magnetic Nanoparticles

Herein, the synthesis and catalytic activity of two ephedrine-based catalysts and two ephedrine-based magnetic nanoparticle-supported catalysts are reported. All catalysts developed were tested in the addition of diethylzinc to aromatic aldehydes and in the Henry reaction. The homogeneous catalysts showed moderate catalytic activity in the organozinc addition and good activity in the Henry reaction, whereas in the case of the nanocatalyst, it was not effective in the addition of diethylzinc to aldehydes and gave reasonable results in the Henry reaction. Moreover, the nanocatalyst remained unchanged over the course of up to three catalytic cycles. To the best of our knowledge, the proposed system is the first recyclable ephedrine-based magnetic nanocatalyst employed in an enantioselective reaction.

A Review of the Ephedra genus: Distribution, Ecology, Ethnobotany, Phytochemistry and Pharmacological Properties

Ephedra is one of the largest genera of the Ephedraceae family, which is distributed in arid and semiarid regions of the world. In the traditional medicine from several countries some species from the genus are commonly used to treat asthma, cold, flu, chills, fever, headache, nasal congestion, and cough. The chemical constituents of Ephedra species have been of research interest for decades due to their contents of ephedrine-type alkaloids and its pharmacological properties. Other chemical constituents such as phenolic and amino acid derivatives also have resulted attractive and have provided evidence-based supporting of the ethnomedical uses of the Ephedra species. In recent years, research has been expanded to explore the endophytic fungal diversity associated to Ephedra species, as well as, the chemical constituents derived from these fungi and their pharmacological bioprospecting. Two additional aspects that illustrate the chemical diversity of Ephedra genus are the chemotaxonomy approaches and the use of ephedrine-type alkaloids as building blocks in organic synthesis. American Ephedra species, especially those that exist in Mexico, are considered to lack ephedrine type alkaloids. In this sense, the phytochemical study of Mexican Ephedra species is a promising area of research to corroborate their ephedrine-type alkaloids content and, in turn, discover new chemical compounds with potential biological activity. Therefore, the present review represents a key compilation of all the relevant information for the Ephedra genus, in particular the American species, the species distribution, their ecological interactions, its ethnobotany, its phytochemistry and their pharmacological activities and toxicities, in order to promote clear directions for future research.

Concise Total Synthesis of (-)-Affinisine Oxindole, (+)-Isoalstonisine, (+)-Alstofoline, (-)-Macrogentine, (+)-Na -Demethylalstonisine, (-)-Alstonoxine A, and (+)-Alstonisine

A highly enantio- and diastereoselective strategy to access any member of the sarpagine/macroline family of oxindole alkaloids via internal asymmetric induction was developed from readily available d-(+)-tryptophan. At the center of this approach was the diastereospecific generation of the spiro[pyrrolidine-3,3'-oxindole] moiety at an early stage via a tert-butyl hypochlorite-promoted oxidative rearrangement of a chiral tetrahydro-β-carboline derivative. This key branching point determined the spatial configuration at the C-7 spiro center to be entirely 7R or 7S. Other key stereospecific processes were the asymmetric Pictet-Spengler reaction and Dieckmann cyclization, which were scalable to the 600 and 150 gram levels, respectively. Execution of this approach resulted in first enantiospecific total synthesis of (+)-isoalstonisine and (-)-macrogentine from the chitosenine series (7R), as well as (+)-alstonisine, (+)-alstofoline, (-)-alstonoxine A and (+)-Na -demethylalstonisine from the alstonisine series (7S).

Enantioselective addition of dialkylzinc to aromatic aldimines mediated by camphor-derived chiral β-amino alcohols

The enantioselective addition of diethylzinc or dimethylzinc to N-(diphenylphosphinoyl)imines mediated by 1 or 2 could be achieved in high yields (70-97 %) and enantioselectivities (85-98 % ee). The catalytic loading of 1 or 2 a could be reduced to 10 mol % for methylation or ethylation of imines in high yields and enantioselectivities (79-96 %) when the reaction was conducted in the presence of 1.8 equiv of methanol. N-Monosubstituted amino alcohols induced higher enantioselectivity than their N,N-disubstituted congener in our catalytic system.