scholarly journals X-Ray crystallography and the chemistry of the steroids. Part I

1940 ◽  
Vol 239 (802) ◽  
pp. 135-182 ◽  
Keyword(s):  
Crystal Morphology ◽  
Ring System ◽  
Higher Plant ◽  
X Ray ◽  
X Ray Crystallography ◽  
Unit Cell Size ◽  
Molecular Arrangement ◽  
Preliminary Examination ◽  
Optic Orientation ◽  
Shape And Size

A survey has been made of the X-ray crystallography of some eighty sterol derivatives belonging mainly to the cholesterol and ergosterol series but including also calciferol and other photoderivatives of ergosterol and some higher plant and animal sterols. The measurements are recorded in four tables and include determinations of unit cell size, space group and some data on the crystal morphology and optics. In three cases, cholesteryl chloride, bromide and cholesteryl chloride hydrochloride, Patterson projections have also been derived from the intensities of the X-ray reflexions of the hOl planes. These confirm earlier deductions on the shape and size of the sterol molecules, proving that these are roughly lath-shaped, 20 x 7 x 4 A, and the details of the patterns can also to some degree be correlated with the actual arrangement of the carbon atoms in the sterol ring system and with the positions of the chlorine and bromine atoms. The arrangement of the molecules in the crystal units is closely that given by the preliminary examination from the optic orientation, and this has therefore been employed to suggest in each of the remaining sterol crystal structures the probable molecular arrangement

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>

Addition reactions of a dialkyl- and a diarylsilylene to cyanides RCN: Different pathways? (1)

2000 ◽  
Vol 78 (11) ◽  
pp. 1469-1473 ◽  
Author(s):  
Manfred Weidenbruch ◽  
Frank Meiners ◽  
Wolfgang Saak
Keyword(s):  
Triple Bond ◽  
Ring System ◽  
Addition Reactions ◽  
X Ray ◽  
X Ray Crystallography

Di-tert-butylsilylene, generated by photolysis of hexa-tert-butylcyclotrisilane, reacts with the triple bond of adamantane-1-carbonitrile to furnish the 1,3-diaza-2,5-disilacyclohexa-3,6-diene 5. However, treatment of 2,2-dimethylpropanenitrile with dimesitylsilylene affords the azadisilacyclobutene ring system 6. The structures of 5 and 6 were determined by X-ray crystallography.Key words: silicon, silylene, silaheterocycles, X-ray crystallography.

scholarly journals 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>

scholarly journals Crystal structure of glutamate-1-semialdehyde-2,1-aminomutase fromArabidopsis thaliana

2016 ◽  
Vol 72 (6) ◽  
pp. 448-456 ◽  
Author(s):  
Yingxian Song ◽  
Hua Pu ◽  
Tian Jiang ◽  
Lixin Zhang ◽  
Min Ouyang
Keyword(s):  
Crystal Structure ◽  
Arabidopsis Thaliana ◽  
Function Analysis ◽  
The Other ◽  
Negative Cooperativity ◽  
Higher Plant ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cofactor Binding ◽  
Asymmetric Dimer

Glutamate-1-semialdehyde-2,1-aminomutase (GSAM) catalyzes the isomerization of glutamate-1-semialdehyde (GSA) to 5-aminolevulinate (ALA) and is distributed in archaea, most bacteria and plants. Although structures of GSAM from archaea and bacteria have been resolved, a GSAM structure from a higher plant is not available, preventing further structure–function analysis. Here, the structure of GSAM fromArabidopsis thaliana(AtGSA1) obtained by X-ray crystallography is reported at 1.25 Å resolution.AtGSA1 forms an asymmetric dimer and displays asymmetry in cofactor binding as well as in the gating-loop orientation, which is consistent with previously reportedSynechococcusGSAM structures. While one monomer binds PMP with the gating loop fixed in the open state, the other monomer binds either PMP or PLP and the gating loop is ready to close. The data also reveal the mobility of residues Gly163, Ser164 and Gly165, which are important for reorientation of the gating loop. Furthermore, the asymmetry of theAtGSA1 structure supports the previously proposed negative cooperativity between monomers of GSAM.

scholarly journals Ring D-Modified and Highly Reduced Angucyclinones From Marine Sediment-Derived Streptomyces sp.

2021 ◽  
Vol 9 ◽  
Author(s):  
Lin Guo ◽  
Qiaoli Yang ◽  
Guangfei Wang ◽  
Shumin Zhang ◽  
Ming Liu ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Natural Products ◽  
Positive Control ◽  
Ring System ◽  
Antibiotic Activity ◽  
Type Ii ◽  
New Members ◽  
Streptomyces Sp ◽  
X Ray ◽  
X Ray Crystallography

Angucyclines and angucyclinones represent the largest family of type II PKS-engineered natural products. Chemical analysis of a marine Streptomyces sp. KCB-132 yielded three new members, actetrophenone A (1) and actetrophenols A–B (2–3). Their structures were elucidated by NMR spectroscopy, X-ray crystallography and CD calculations. Actetrophenone A (1) is the first representative of a novel-type angucyclinone bearing a nonaromatic D-ring. Actetrophenol A (2) features a highly reduced and aromatized four-ring system, which is unprecedented for natural products. While (Ra)- and (Sa)-actetrophenol B (3) bear an unprecedented N-acetyltryptamine-substituted tetraphene core skeleton, this is the first report of a pair of atropisomeric isomers in the angucyclinone family. Actetrophenol A (2) exhibits remarkable antibiotic activity, notably including potent activity to multiple resistant Staphylococcus aureus and Enterococcus faecium with MIC values of 4 μg/ml, in contrast, the positive control antimicrobial agent penicillin was inactive up to 32 μg/ml.

scholarly journals N-Benzyl-3,5-dideoxy-3,5-imino-1,2-O-isopropylidene-β-L-lyxofuranose

2012 ◽  
Vol 68 (8) ◽  
pp. o2410-o2410
Author(s):  
David S. Edgeley ◽  
Sarah F. Jenkinson ◽  
Gabriel Lenagh-Snow ◽  
Catherine Rutherford ◽  
George W. J. Fleet ◽  
...  
Keyword(s):  
Absolute Configuration ◽  
Title Compound ◽  
Ring System ◽  
Starting Material ◽  
X Ray ◽  
X Ray Crystallography ◽  
Compound C ◽  
Relative Stereochemistry ◽  
The Absolute

X-ray crystallography confirmed the formation, structure and relative stereochemistry of the title compound, C15H19NO3, which contains a sterically congested four-membered azetidine ring system. The absolute configuration was determined by the use of L-arabinose as the starting material.

scholarly journals Sulfuric acid and Amberlyst-H+ catalyzed condensation reactions of renewable keto acids with paraformaldehyde: synthesis of a new dispiro bis-lactone ring system 2,9,13-trioxadispiro[4.1.4.3]tetradecane-3,6,10-trione

RSC Advances ◽  
2017 ◽  
Vol 7 (39) ◽  
pp. 23917-23923 ◽  
Author(s):  
Ananda S. Amarasekara ◽  
Uyen Ha ◽  
Marina S. Fonari ◽  
Shabari Nath Bejagam ◽  
Davor Margetić
Keyword(s):  
Sulfuric Acid ◽  
Levulinic Acid ◽  
Lactone Ring ◽  
Ring System ◽  
X Ray ◽  
X Ray Crystallography ◽  
Condensation Reactions ◽  
Keto Acids ◽  
Acid Catalyzed

The acid catalyzed condensation of levulinic acid with paraformaldehyde at 80 °C gives 2,9,11,14-tetraoxadispiro[4.1.5.3]pentadecane-3,6-dione, in which the structure was confirmed by X-ray crystallography.

Removal of salt from a salt-induced protein crystal without cross-linking. Preliminary examination of "desalted" crystals of phosphoglucomutase by x-ray crystallography at low temperature

Biochemistry ◽  
1991 ◽  
Vol 30 (28) ◽  
pp. 6866-6875 ◽  
Author(s):  
William J. Ray ◽  
Jeffrey T. Bolin ◽  
Joseph M. Puvathingal ◽  
Wladyslaw Minor ◽  
Yiwei Liu ◽  
...  
Keyword(s):  
Low Temperature ◽  
Protein Crystal ◽  
Cross Linking ◽  
X Ray ◽  
X Ray Crystallography ◽  
Preliminary Examination
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