scholarly journals cis–trans Isomerization of silybins A and B

2014 ◽  
Vol 10 ◽  
pp. 1047-1063 ◽  
Author(s):  
Michaela Novotná ◽  
Radek Gažák ◽  
David Biedermann ◽  
Florent Di Meo ◽  
Petr Marhol ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Absolute Configuration ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Model Compounds ◽  
Electronic Circular Dichroism ◽  
Trans Isomerization ◽  
Pure Compounds ◽  
Acid Catalyzed ◽  
Optically Pure

Methods were developed and optimized for the preparation of the 2,3-cis- and the 10,11-cis-isomers of silybin by the Lewis acid catalyzed (BF3∙OEt2) isomerization of silybins A (1a) and B (1b) (trans-isomers). The absolute configuration of all optically pure compounds was determined by using NMR and comparing their electronic circular dichroism data with model compounds of known absolute configurations. Mechanisms for cis–trans-isomerization of silybin are proposed and supported by quantum mechanical calculations.

Effects of Enantiomerically Pure β-Carboline Alkaloids from Picrasma quassioides on Human Hepatoma Cells

Planta Medica ◽  
2019 ◽  
Vol 85 (08) ◽  
pp. 648-656 ◽  
Author(s):  
Wen-Yu Zhao ◽  
Jing-Jie Chen ◽  
Chun-Xin Zou ◽  
Wei-Yu Zhou ◽  
Guo-Dong Yao ◽  
...  
Keyword(s):  
Hepg2 Cells ◽  
Biosynthetic Pathway ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Human Hepatoma ◽  
Human Hepatoma Cells ◽  
Enantiomerically Pure ◽  
Spectroscopic Analyses ◽  
Picrasma Quassioides ◽  
Pure Compounds

AbstractFour pairs of β-carboline enantiomers (1a/1b–4a/4b), 2 β-carboline derivatives (5 – 6) with a single enantiomeric configuration, together with 2 known achiral congeners (7 – 8) were isolated from the stems of Picrasma quassioides. Their structures were elucidated on the basis of extensive spectroscopic analyses and quantum mechanical calculations. Compound 5 possesses a 4,5-seco β-carboline framework and represents the first example of this type of β-carboline alkaloids from nature. A possible biosynthetic pathway is proposed to generate the racemate 4 and the enantiomerically pure compounds 5 and 6. All isolates were screened for their cytotoxicity against hepatocellular carcinoma Hep3B and HepG2 cells, which revealed that enantiomeric compounds 4a and 4b had distinctive effects in HepG2 cells. Further investigation showed that 4b could induce apoptosis in HepG2 cells.

Recent Advances in Enantioselective Brønsted Base Organocatalytic Reactions

Synlett ◽  
2017 ◽  
Vol 28 (11) ◽  
pp. 1272-1277 ◽  
Author(s):  
Choon-Hong Tan ◽  
Bo Teng ◽  
Wei Lim
Keyword(s):  
Lewis Acid ◽  
Ion Pair ◽  
Acidic Proton ◽  
Pure Compounds ◽  
Brønsted Base ◽  
Electron Withdrawing Group ◽  
Dual Activation ◽  
Catalyzed Reactions ◽  
Organocatalytic Reactions ◽  
Optically Pure

Enantioselective Brønsted base catalyzed reactions have established themselves as powerful tools for the construction of optically pure compounds. Most strategies aim at improving these reactions involve the modification of substrates to decrease the pK a of the acidic proton. Typically, an electron-withdrawing group such as an ester or a fluorine is placed at the α-carbon, where the proton is also residing. The activation of less active proton, thus, becomes a major challenge in this field of research. In order to overcome this pK a barrier, some new innovative approaches have been demonstrated in recent years. The implementation of dual activation modes and the development of organocatalytic Brønsted superbases are selected to be discussed in this minireview.1 Introduction2 Dual Activation Using Lewis Acid and Brønsted Base3 Dual Activation Using Iminium Catalyst and Brønsted Base4 Chiral Brønsted Superbase5 Chiral Ion-Pair Brønsted Base6 Summary and Outlook

Simple Synthesis of Complex Amines from the Diels–Alder Adducts of (–)-Cytisine

Synthesis ◽  
2021 ◽  
Author(s):  
Alexander Shivanyuk ◽  
Alexey Chuyko ◽  
Grygoriy Dolgonos ◽  
Volodymyr Fetyukhin ◽  
Oleg Lukin
Keyword(s):  
Quantum Chemical ◽  
Alder Reaction ◽  
Diels Alder ◽  
Secondary Amines ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Carbonyl Groups ◽  
Model Compounds ◽  
Reaction Progress ◽  
Diels Alder Reaction

AbstractThe Diels–Alder reaction of N-benzylcytisine with N-methyl- and N-benzylmaleimides is 100% endo-selective and gives the corresponding syn- and anti-diastereomers in 11–42% isolated yields. The studies of the reaction progress with LCMS and NMR along with detailed quantum chemical calculations revealed that some Diels–Alder adducts are kinetically and their isomers are thermodynamically controlled products. The Pd/C-catalyzed hydrogenation of benzyl-protected cytisine amine derivatives resulted in the removal of the benzyl group and the addition of hydrogen to the C=C double bond to give the corresponding secondary amines in 45–84% yield. The complete reduction of carbonyl groups in a cytisine derivative with LiAlH4 in THF under reflux afforded the respective tricyclic triamine. Quantum mechanical calculations for the mechanism of the Diels–Alder reaction between the simplest model compounds are presented.

scholarly journals A Chiral Sulfoxide-Based C–H Acid

Synlett ◽  
2021 ◽  
Author(s):  
Benjamin List ◽  
Denis Höfler ◽  
Karl Kaupmees ◽  
Ivo Leito
Keyword(s):  
Single Crystal ◽  
Lewis Acid ◽  
Absolute Configuration ◽  
X Ray ◽  
Design And Synthesis ◽  
High Acidity ◽  
Acid Catalyzed ◽  
Brønsted And Lewis Acid

We report the design and synthesis of a strong, chiral, enantiopure sulfoxide-based C–H acid. Single crystal X-ray analysis confirms the proposed structure and its absolute configuration. The new motif shows a high acidity and activity in Brønsted and Lewis acid catalyzed transformations. So far, only low enantioselectivities were achieved.

NIS, IR and Raman spectra with quantum mechanical calculations for analyzing the force field of hypericin model compounds

1999 ◽  
Author(s):  
Jozef Ulicny ◽  
Nicolas Leulliot ◽  
Lydie Grajcar ◽  
Marie-Hélène Baron ◽  
Hervé Jobic ◽  
...  
Keyword(s):  
Force Field ◽  
Raman Spectra ◽  
Ir And Raman Spectra ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Model Compounds ◽  
Ir And Raman
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