scholarly journals Rearrangements during deamination of 4-amino-4-des(oxymethylene)anhydro-lycoctonam

1981 ◽  
Vol 59 (21) ◽  
pp. 3039-3043 ◽  
Author(s):  
O. E. Edwards
Keyword(s):  
Nitrous Acid ◽  
Skeletal Rearrangement ◽  
Diterpenoid Alkaloid ◽  
X Ray ◽  
X Ray Crystallography

The diterpenoid alkaloid lycoctonine was transformed into 4-amino-4-des(oxymethylene)anhydrolycoctonam. Nitrous acid deamination of this led to two unexpected products, an aldehydo-lactam acid and a hydroxy-keto lactam, both involving skeletal rearrangement. The origin of these products is discussed on the basis of structures determined by X-ray crystallography.

Reaction of γ-nitro ketones with thionyl chloride: formation and X-ray crystal structure of an α-sulfinyl ketone

1984 ◽  
Vol 37 (4) ◽  
pp. 777 ◽  
Author(s):  
DSC Black ◽  
GD Fallon ◽  
BM Gatehouse ◽  
JD Wishart
Keyword(s):  
Crystal Structure ◽  
Thionyl Chloride ◽  
Nitrous Acid ◽  
Acid Treatment ◽  
Base Hydrolysis ◽  
Group Effect ◽  
X Ray ◽  
X Ray Crystallography ◽  
Unusual Formation

Reaction of thionyl chloride on 4-methyl-4-nitro-1-phenylpentan-1-one (2) yields 4-methyl-4-nitro- 1-phenyl-2-thioxopentan-1-one S-oxide (4), the structure of which has been clarified by X-ray crystallography. The corresponding methoxyphenyl compound (10) has been obtained similarly. The sulfinyl ketone (4) underwent base hydrolysis to the methylene ketone (2) and photoconversion into the diketone (12), which was independently prepared by nitrous acid treatment of the hydroxyimino ketone (11). The unusual formation of the sulfinyl ketones (4) and (10) appears selective for the reaction with unhindered γ-nitro ketones and arises on account of a neighbouring group effect from the nitro substituent.

Skeletal Rearrangement in the Ritter Reaction of Turpentine: A Novel Synthesis of P-menthane Diamides

2017 ◽  
Vol 41 (2) ◽  
pp. 124-127 ◽  
Author(s):  
Shi-Chao Xu ◽  
Shou-Ji Zhu ◽  
Yu-Xiang Chen ◽  
Jing Wang ◽  
Liang-Wu Bi ◽  
...  
Keyword(s):  
Reaction Mechanism ◽  
Ritter Reaction ◽  
Skeletal Rearrangement ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Novel Synthesis ◽  
Probable Reaction Mechanism ◽  
Probable Reaction ◽  
The Ritter Reaction

A novel skeletal rearrangement in the Ritter reaction was examined which conveniently generated p-menthane diamides from turpentine. A probable reaction mechanism was proposed based on employing thermodynamic analysis. All the products were purified and characterised by 1H NMR, IR, X-ray crystallography and ESI+-MS.

Difference Fourier Analysis of Glucose Embedded and Frozen Hydrated Purple Membrane

1982 ◽  
Vol 40 ◽  
pp. 74-75
Author(s):  
Jules S. Jaffe ◽  
Robert M. Glaeser
Keyword(s):  
Purple Membrane ◽  
Data Set ◽  
High Resolution Data ◽  
X Ray ◽  
X Ray Crystallography ◽  
Fourier Techniques ◽  
Versus Protein ◽  
The Difference ◽  
Difference Fourier ◽  
Ideal Method

Although difference Fourier techniques are standard in X-ray crystallography it has only been very recently that electron crystallographers have been able to take advantage of this method. We have combined a high resolution data set for frozen glucose embedded Purple Membrane (PM) with a data set collected from PM prepared in the frozen hydrated state in order to visualize any differences in structure due to the different methods of preparation. The increased contrast between protein-ice versus protein-glucose may prove to be an advantage of the frozen hydrated technique for visualizing those parts of bacteriorhodopsin that are embedded in glucose. In addition, surface groups of the protein may be disordered in glucose and ordered in the frozen state. The sensitivity of the difference Fourier technique to small changes in structure provides an ideal method for testing this hypothesis.

3-D reconstruction of molecular shape from microcrystal thin sections

1983 ◽  
Vol 41 ◽  
pp. 748-749
Author(s):  
S. Cusack ◽  
J.-C. Jésior
Keyword(s):  
Three Dimensional ◽  
Molecular Shape ◽  
Biological Molecules ◽  
Fourier Space ◽  
Single Particles ◽  
Thin Sections ◽  
Standard Methods ◽  
X Ray ◽  
X Ray Crystallography ◽  
Dimensional Reconstruction

Three-dimensional reconstruction techniques using electron microscopy have been principally developed for application to 2-D arrays (i.e. monolayers) of biological molecules and symmetrical single particles (e.g. helical viruses). However many biological molecules that crystallise form multilayered microcrystals which are unsuitable for study by either the standard methods of 3-D reconstruction or, because of their size, by X-ray crystallography. The grid sectioning technique enables a number of different projections of such microcrystals to be obtained in well defined directions (e.g. parallel to crystal axes) and poses the problem of how best these projections can be used to reconstruct the packing and shape of the molecules forming the microcrystal.Given sufficient projections there may be enough information to do a crystallographic reconstruction in Fourier space. We however have considered the situation where only a limited number of projections are available, as for example in the case of catalase platelets where three orthogonal and two diagonal projections have been obtained (Fig. 1).

Electron microscopy of rabbit FC crystals

1983 ◽  
Vol 41 ◽  
pp. 730-731
Author(s):  
Robert A. Grant ◽  
Laura L. Degn ◽  
Wah Chiu ◽  
John Robinson
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Molecular Replacement ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Replacement Technique ◽  
Hydrated Crystal ◽  
Molecular Structure Analysis

Proteolytic digestion of the immunoglobulin IgG with papain cleaves the molecule into an antigen binding fragment, Fab, and a compliment binding fragment, Fc. Structures of intact immunoglobulin, Fab and Fc from various sources have been solved by X-ray crystallography. Rabbit Fc can be crystallized as thin platelets suitable for high resolution electron microscopy. The structure of rabbit Fc can be expected to be similar to the known structure of human Fc, making it an ideal specimen for comparing the X-ray and electron crystallographic techniques and for the application of the molecular replacement technique to electron crystallography. Thin protein crystals embedded in ice diffract to high resolution. A low resolution image of a frozen, hydrated crystal can be expected to have a better contrast than a glucose embedded crystal due to the larger density difference between protein and ice compared to protein and glucose. For these reasons we are using an ice embedding technique to prepare the rabbit Fc crystals for molecular structure analysis by electron microscopy.

Tele-Substitution Reactions in the Synthesis of a Promising Class of Antimalarials

2020 ◽  
Author(s):  
Marat Korsik ◽  
Edwin Tse ◽  
David Smith ◽  
William Lewis ◽  
Peter J. Rutledge ◽  
...  
Keyword(s):  
Heterocyclic Ring ◽  
Ring System ◽  
Substitution Reactions ◽  
Laboratory Notebook ◽  
Polar Solvents ◽  
X Ray ◽  
X Ray Crystallography ◽  
The Core ◽  
Nmr Data

<p></p><p>We have discovered and studied a <i>tele</i>substitution reaction in a biologically important heterocyclic ring system. Conditions that favour the <i>tele</i>-substitution pathway were identified: the use of increased equivalents of the nucleophile or decreased equivalents of base, or the use of softer nucleophiles, less polar solvents and larger halogens on the electrophile. Using results from X-ray crystallography and isotope labelling experiments a mechanism for this unusual transformation is proposed. We focused on this triazolopyrazine as it is the core structure of the <i>in vivo </i>active anti-plasmodium compounds of Series 4 of the Open Source Malaria consortium.</p> <p> </p> <p>Archive of the electronic laboratory notebook with the description of all conducted experiments and raw NMR data could be accessed via following link <a href="https://ses.library.usyd.edu.au/handle/2123/21890">https://ses.library.usyd.edu.au/handle/2123/21890</a> . For navigation between entries of laboratory notebook please use file "Strings for compounds in the article.pdf" that works as a reference between article codes and notebook codes, also this file contain SMILES for these compounds. </p><br><p></p>

Highly Electron-Deficient Pyridinium-Nitrones for Rapid and Tunable Inverse-Electron-Demand Strain-Promoted Alkyne-Nitrone Cycloaddition to Bicyclo[6.1.0]nonyne

2019 ◽  
Author(s):  
Praveen Gunawardene ◽  
Wilson Luo ◽  
Alexander M. Polgar ◽  
John F. Corrigan ◽  
Mark Workentin
Keyword(s):  
Density Functional Theory ◽  
Reaction Kinetics ◽  
Density Functional ◽  
Functional Theory ◽  
X Ray ◽  
Inverse Electron Demand ◽  
X Ray Crystallography ◽  
Electron Demand

<div> <div> <p>Highly accelerated inverse-electron-demand strain-promoted alkyne-nitrone cycloaddition (IED SPANC) between a sta- ble cyclooctyne (bicyclo[6.1.0]nonyne (BCN)) and nitrones delocalized into a Cα-pyridinium functionality is reported, with the most electron-deficient “pyridinium-nitrone” displaying among the most rapid cycloadditions to BCN that is currently reported. Density functional theory (DFT) and X-ray crystallography are explored to rationalize the effects of N- and Cα-substituent modifications at the nitrone on IED SPANC reaction kinetics and the overall rapid reactivity of pyridinium-delocalized nitrones.</p> </div> </div>

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