Synthesis of (±)-14-epi-hydroxydolasta-1(15),7,9-triene and (±)-7-epi-acetoxy-14-epi-hydroxydolasta-1(15),8-diene*Taken in part from the Ph.D. dissertation of Jianhua Yu, University of Georgia, Athens, Georgia, USA, 2009.

2012 ◽  
Vol 90 (1) ◽  
pp. 75-84 ◽  
Author(s):  
George Majetich ◽  
Jianhua Yu
Keyword(s):  
Methyl Groups ◽  
Cyclization Product ◽  
Facile Synthesis ◽  
X Ray ◽  
X Ray Crystallography ◽  
University Of Georgia ◽  
Salient Features ◽  
Relationship Of

1,3-Dimethyl-2-nitrobenzene was converted to the key intramolecular Friedel–Crafts intermediate 24 in ten steps. Treatment of 24 with TiCl4 produced tricyclic enone 25 in 61%–75% yield, having the requisite trans relationship of the two angular methyl groups and many of the salient features of the dolastane diterpenes. The structure of enone 25 was verified by X-ray crystallography analysis. Cyclization product 25 permitted the facile synthesis of (±)-14-epi-hydroxydolasta-1(15),7,9-triene and (±)-7-epi-acetoxy-14-epi-hydroxydolasta-1(15),8-diene, which are detailed in this article.

scholarly journals Rational synthesis of an atomically precise carboncone under mild conditions

2019 ◽  
Vol 5 (8) ◽  
pp. eaaw0982 ◽  
Author(s):  
Zheng-Zhong Zhu ◽  
Zuo-Chang Chen ◽  
Yang-Rong Yao ◽  
Cun-Hao Cui ◽  
Shu-Hui Li ◽  
...  
Keyword(s):  
Apex Angle ◽  
Facile Synthesis ◽  
Reaction Conditions ◽  
X Ray ◽  
Carbon Allotropes ◽  
X Ray Crystallography ◽  
Mild Conditions ◽  
Research Opportunity ◽  
Insight Into ◽  
Structural Strain

Carboncones, a special family of all-carbon allotropes, are predicted to have unique properties that distinguish them from fullerenes, carbon nanotubes, and graphenes. Owing to the absence of methods to synthesize atomically well-defined carboncones, however, experimental insight into the nature of pure carboncones has been inaccessible. Herein, we describe a facile synthesis of an atomically well-defined carboncone[1,2] (C70H20) and its soluble penta-mesityl derivative. Identified by x-ray crystallography, the carbon skeleton is a carboncone with the largest possible apex angle. Much of the structural strain is overcome in the final step of converting the bowl-shaped precursor into the rigid carboncone under mild reaction conditions. This work provides a research opportunity for investigations of atomically precise single-layered carboncones having even higher cone walls and/or smaller apex angles.

A Facile Synthesis of a 2,2,3,3-Tetrasubstituted Tetrahydropyran

1991 ◽  
Vol 44 (8) ◽  
pp. 1115
Author(s):  
DJ Brecknell ◽  
RM Carman ◽  
WT Robinson ◽  
RC Schumann
Keyword(s):  
Major Product ◽  
Single Bond ◽  
Facile Synthesis ◽  
X Ray ◽  
X Ray Crystallography

An unusually facile acid- catalysed condensation has been observed between acetone and the unsaturated diol (3), producing a mixture of isomeric bicyclic tetrahydropyrans (6) and (8), with the formation of a new fully substituted carbon-carbon single bond. The structures were determined by n.m.r. and that of the major product (6) was confirmed by X-ray crystallography.

The Conformation of Crystalline Di[3-(4'-methoxyphenyl)-2,2,4,4-tetramethylpentan-3-yl] Oxalate

1996 ◽  
Vol 49 (10) ◽  
pp. 1171 ◽  
Author(s):  
DJ Collins ◽  
M Dosen ◽  
GD Fallon ◽  
HA Jacobs ◽  
GF Meijs ◽  
...  
Keyword(s):  
Benzene Ring ◽  
X Ray ◽  
X Ray Crystallography ◽  
Tetrahydropyranyl Ether ◽  
Relationship Of

Di [3-(4'-methoxyphenyl)-2,2,4,4-tetramethylpentan-3-yl] oxalate (4a) and the analogous bis tetrahydropyranyl ether (4b) have been synthesized, and X-ray crystallography of the former shows an almost symmetrically staggered relationship of the t-butyl groups with respect to the plane of the benzene ring.

Six pyrimidonium salts: determination of their crystal structures and studies of their prototropic behaviour in solution

1984 ◽  
Vol 62 (6) ◽  
pp. 1194-1202 ◽  
Author(s):  
Thomas W. S. Lee ◽  
Steven J. Rettig ◽  
Ross Stewart ◽  
James Trotter
Keyword(s):  
Hydrogen Exchange ◽  
Molecular Geometry ◽  
High Reactivity ◽  
Methyl Groups ◽  
Contributing Factors ◽  
X Ray ◽  
X Ray Crystallography ◽  
Reactive Compound ◽  
Chloride Salts

Six methyl-substituted 2-pyrimidonium chloride salts have been prepared and the rates of hydrogen exchange of their reactive methyl groups (at the 4- and 6-positions) have been determined in DCl/D2O solution. Adjacent methyl groups, whether on nitrogen or carbon, activate the exchanging centres, whereas more distant methyl groups have a deactivating effect. The molecular geometry of the salts has been determined by X-ray crystallography with the view to determining whether the presence of strain in the pyrimidonium ring can account for the activating effect of adjacent methyl. The most reactive compound, the 1,5,6-trimethylpyrimidonium chloride, has a geometry that is consistent with high reactivity, viz. a non-planar ring and short H … H intermethyl distance. However, the 1,4,5,6-tetramethyl compound, which also is non-planar and has an extremely short 5-6 intermethyl distance (1.99 Å), is not highly reactive; that is, the heightened strain is unable to overcome the deactivating inductive effect of the additional methyl group. We conclude that deviations from ring planarity and short intermethyl distances are insufficient to account for the activation produced by adjacent methyl though they appear to be contributing factors to this effect.

scholarly journals Insights into the formation of chiral second sphere coordination complexes with aromatic tris amines: combined single crystal X-ray crystallography and molecular modeling analyses

2015 ◽  
Vol 44 (36) ◽  
pp. 15960-15965 ◽  
Author(s):  
Hong-Cui Yu ◽  
Lei Li ◽  
Ji Gao ◽  
Jian Tong ◽  
Wenxu Zheng ◽  
...  
Keyword(s):  
Molecular Modeling ◽  
Single Crystal ◽  
Aromatic Ring ◽  
Coordination Complexes ◽  
Methyl Groups ◽  
X Ray ◽  
X Ray Crystallography

Bulky methyl groups on the central aromatic ring in chiral isostructural second sphere coordination adducts are crucial for the induction of chirality.

Facile synthesis of model 2,4-diaryl-1,3,4-thiadiazino[5,6-h]fluoroquinolones

2019 ◽  
Vol 74 (6) ◽  
pp. 507-512
Author(s):  
Mohammed M. Abadleh ◽  
Tawfiq Arafat ◽  
Luay Abu-Qatouseh ◽  
Mustafa M. El-Abadelah ◽  
Firas F. Awwadi ◽  
...  
Keyword(s):  
Single Crystal ◽  
Spectral Data ◽  
Carboxylic Acids ◽  
Facile Synthesis ◽  
X Ray ◽  
X Ray Crystallography

AbstractA Selected set of 2,4-diaryl-7-oxo-1,2,4-thiadiazino[5,6-h]quinoline-8-carboxylic acids 6a–e has been prepared via reaction of the parent 7-chloro-8-nitro-10-cyclopropyl-6-fluoroquinolone 4 with the appropriate N′-(aryl)benzothiohydrazide 5a–e in presence of triethylamine. Structures of the new heterocyclics 6a–e are supported by spectral data and confirmed by single-crystal X-ray crystallography for 6a.

Chemical Shift. V. Further Studies on the Long-range Shielding Effects of the C—H and C=O Bonds

1971 ◽  
Vol 49 (9) ◽  
pp. 1328-1334 ◽  
Author(s):  
J. W. ApSimon ◽  
H. Beierberck
Keyword(s):  
Chemical Shift ◽  
Magnetic Anisotropy ◽  
Long Range ◽  
Methyl Groups ◽  
X Ray ◽  
X Ray Crystallography ◽  
Geometric Factors ◽  
Atomic Coordinates ◽  
Shielding Effects

The long-range shielding effects of the C=O and C—H bonds were reexamined by the method described in part IV of this series, with the objective of resolving the discrepancies between some of the conclusions presented and earlier findings by Zürcher. The C—H bond magnetic anisotropy was treated as a variable and found to be small enough to be negligible. Upon omission of this term, both electrostatic and magnetic anisotropy effects had to be invoked to account for the shielding effects of the carbonyl group.The necessary geometric quantities were calculated from atomic coordinates for androsterone, as determined by X-ray crystallography, and freely rotating methyl groups were approximated by superpositions of 24 conformations of the group. The results were in essential agreement with those obtained with the use of geometric factors computed as described in part IV.

Structure and wavelength modification in retinylidene iminium salts

1996 ◽  
Vol 74 (4) ◽  
pp. 591-601 ◽  
Author(s):  
George R. Elia ◽  
Ronald F. Childs ◽  
James F. Britten ◽  
Daniel S.C. Yang ◽  
Bernard D. Santarsiero
Keyword(s):  
Solid State ◽  
Alkyl Substituent ◽  
Spectroscopic Properties ◽  
Crystal Lattices ◽  
Charge Delocalization ◽  
X Ray ◽  
X Ray Crystallography ◽  
Iminium Salts ◽  
Internuclear Distances ◽  
Relationship Of

The spectroscopic and structural properties of the perchlorate and triflate salts of N-n-butyl-retinylidene imine, 2 and 3, have been examined in solution and solid phases. In solution these salts were found to exhibit very similar UV and NMR spectroscopic properties. However, in the solid state marked differences in their absorption spectra (2, λmax = 504 nm; 3, λmax = 445 nm) and 13C NMR spectra were found. The structures of the two salts were determined by X-ray crystallography. The cations in each of the salts were shown to have very similar conformations, detailed structures, and packing in their crystal lattices. The differences in the spectroscopic properties of the salts in the solid state could not be accounted for on the basis of any structural differences in the cations themselves. In terms of cation–anion interactions, a strong hydrogen bonding interaction was found in each case between the N-H proton and an oxygen atom of the counterion. However, there were significant differences between the two salts in terms of the [Formula: see text] internuclear distances (2, [Formula: see text] and in 3, 2.85(1) Å). The results are strongly suggestive that the wavelength and positive charge delocalization in retinylidène iminium salts are controlled by variation of the distance between the anion and the proton bonded to the Schiff base nitrogen atom. The work reported here represents the first examples of secondary retinylidene iminium salts containing an N-alkyl substituent to be successfully analyzed by X-ray crystallography. The relationship of these observations in the solid state to the spectroscopic properties of the natural visual pigments is explored. Key words: retinylidène iminium salts, iminium salts, cation–anion interactions.

scholarly journals Identification of SARS-CoV2 Main Protease Coldspots Suitable for Drug Targeting

2020 ◽  
Author(s):  
Navaneethakrishnan Krishnamoorthy ◽  
Khalid Fakhro
Keyword(s):  
Active Site ◽  
Missense Mutations ◽  
The Novel ◽  
X Ray ◽  
X Ray Crystallography ◽  
Main Protease ◽  
New Perspective ◽  
Function Relationship ◽  
Novel Coronavirus ◽  
Relationship Of

Abstract Most attempts to target the novel coronavirus SARS-CoV2 are focusing on the main protease (Mpro) 1,2. We already have access to high resolution 3D-structures of the SARS-CoV2 Mpro, which were developed with inhibitors as co-crystals using X-ray crystallography 3-9. However, >19,000 missense mutations in the Mpro have already been reported 10. The mutations encompassing 282 amino acid positions and these “hotspots” might change the Mpro structure and activity, potentially rendering novel antivirals and vaccines ineffective. Here we identified 24 mutational “coldspots” that have resisted mutation since the virus was first detected. We compared the structure-function relationship of these coldspots with several SARS-CoV2 Mpro X-ray crystal structures. We found that three coldspot residues (Leu141, Phe185 and Gln192) help to form the active site, while six (Gly2, Arg4, Tyr126, Lys137, Leu141 and Leu286) contribute to dimer formation that is required for Mpro activity. Importantly, seven coldpots are conserved among other coronaviruses and available on the surface of the active site and at the dimer interface for targeting. The identification and short list of these coldspots offers a new perspective to target the SARS-CoV2 Mpro while avoiding mutation-based drug resistance.

Computational, 1H NMR, and X-ray structural studies on 1-arylurazole tetrazane dimers

2017 ◽  
Vol 73 (9) ◽  
pp. 660-666 ◽  
Author(s):  
Kenneth L. Martin ◽  
Gary W. Breton
Keyword(s):  
Methyl Groups ◽  
Structural Studies ◽  
Aromatic Rings ◽  
Nmr Spectrum ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Dimeric Form ◽  
Shielding Effects

Nitrogen-centered urazole radicals exist in equilibrium with tetrazane dimers in solution. The equilibrium established typically favors the free-radical form. However, 1-arylurazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2-(2,4-dimethylphenyl)-2-[2-(2,4-dimethylphenyl)-4-methyl-3,5-dioxo-1,2,4-triazolidin-1-yl]-4-methyl-1,2,4-triazolidine-3,5-dione, C24H28N6O4, via X-ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6-311G(d,p) level of theory. The preferred syn conformation of these 1-arylurazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some interesting shielding effects of certain signals in the 1H NMR spectrum. Armed with this information, we were able to decipher the more complicated 1H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.

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