Phthalimide-based-SSCF3 reagent for enantioselective dithiotrifluoromethylation

2021 ◽  
Author(s):  
Wen-Chao Gao ◽  
Jianrong Liu ◽  
Xuefeng Jiang
Keyword(s):  
Quaternary Carbon ◽  
Complex Molecules

A novel dithiotrifluoromethylation reagent phthN-SSCF3 was designed and prepared for the incorporation of a SSCF3 unit into complex molecules and the stereoselective construction of a SSCF3-tethered quaternary carbon center.

Alkaline Dissociation Products of Lumbricus Terrestris Hemoglobin Viewed with the STEM

1981 ◽  
Vol 39 ◽  
pp. 434-435
Author(s):  
O. H. Kapp ◽  
M. Ohtsuki ◽  
N. Robin ◽  
S. N. Vinogradov ◽  
A. V. Crewe
Keyword(s):  
Carbon Film ◽  
Lumbricus Terrestris ◽  
Uranyl Acetate ◽  
Acetate Solution ◽  
Oxygen Carriers ◽  
Complex Molecules ◽  
Thin Carbon ◽  
Thin Carbon Film ◽  
Multiple Copies ◽  
Hill Coefficients

Annelid extracellular hemoglobins are among the largest known proteins (M.W = 3.9 x 106), and together with the hemocyanins are the largest known oxygen carriers. They display oxygen affinities generally higher than those o vertebrate hemoglobins with Hill coefficients ranging from slightly higher than unity to values as high as 5-6. These complex molecules are composed of multiple copies of as many as six different polypeptides and posse: approximately 150 hemes per molecule.The samples were diluted to 100-200 μg/ml with distilled water just before application to a thin carbon film (∽15 Å thick). One percent (w/v) uranyl acetate solution was used for negative staining for 2 minutes and dried in air. The specimens were examined with the high resolution STEM. Their general appearance is that of a hexagonal bilayer (Fig. 1), each layer consisting of six spheroidal subunits. The corner to corner hexagonal dimensic is approximately 300 Å and the bilayer thickness approximately 200 Å.

Bleaching ability of pre-hydrolyzed pulps in the context of a biorefinery mill

TAPPI Journal ◽  
2013 ◽  
Vol 12 (11) ◽  
pp. 49-53 ◽  
Author(s):  
CHRISTINE CHIRAT ◽  
LUCIE BOIRON ◽  
DOMINIQUE LACHENAL
Keyword(s):  
Carbon Content ◽  
Acid Hydrolysis ◽  
13C Nmr ◽  
Kraft Lignin ◽  
Kappa Number ◽  
Hydroxyl Groups ◽  
Kraft Pulps ◽  
Quaternary Carbon ◽  
Oxygen Delignification

Autohydrolysis and acid hydrolysis treatments were applied on mixed softwood chips. The cooking ability was studied by varying the alkali and duration of the cook. Pulps with kappa numbers varying from 30 to 70 were obtained. The bleaching ability of these pulps was studied and compared to control kraft pulps. The prehydrolyzed pulps were shown to be more efficiently delignified by oxygen than the control kraft pulps starting from the same kappa number. Furthermore, the final bleaching was also easier for these pulps. It was also shown that extensive oxygen delignification applied on high-kappa pre-hydrolyzed pulps could be a way to improve the overall yield, which is a prerequisite for the development of such biorefinery concepts. Lignin was isolated from the control kraft and the two pre-hydrolyzed kraft pulps and analyzed by 13C NMR. Lignins from pre-hydrolyzed kraft pulps had similar free phenolic groups content to the control kraft lignin, but their aliphatic hydroxyl groups and β-O-4 content were lower than for the control lignin. The quaternary carbon content was the same for all the samples.

Metal-, and Organocatalyst-Free One-Pot Assembly of Chiral Aza-Tricyclic Molecules: Creating Six Contiguous Stereocenters from 2-D-Structures and an Amino Acid

2020 ◽  
Author(s):  
Dung Do
Keyword(s):  
Amino Acid ◽  
Chemical Space ◽  
Structural Diversity ◽  
Therapeutic Agents ◽  
Chiral Molecules ◽  
One Pot ◽  
Complex Molecules ◽  
Chiral Catalyst ◽  
Chiral Complex ◽  
Free Process

<p>Chiral molecules with their defined 3-D structures are of paramount importance for the study of chemical biology and drug discovery. Having rich structural diversity and unique stereoisomerism, chiral molecules offer a large chemical space that can be explored for the design of new therapeutic agents.<sup>1</sup> Practically, chiral architectures are usually prepared from organometallic and organocatalytic processes where a transition metal or an organocatalyst is tailor-made for desired reactions. As a result, developing a method that enables rapid assembly of chiral complex molecules under metal- and organocatalyst-free condition represents a daunting challenge. Here we developed a straightforward route to create a chiral 3-D structure from 2-D structures and an amino acid without any chiral catalyst. The center of this research is the design of a <a>special chiral spiroimidazolidinone cyclohexadienone intermediate</a>, a merger of a chiral reactive substrate with multiple nucleophillic/electrophillic sites and a transient organocatalyst. <a>This unique substrate-catalyst (“subcatalyst”) dual role of the intermediate enhances </a><a>the coordinational proximity of the chiral substrate and catalyst</a> in the key Aza-Michael/Michael cascade resulting in a substantial steric discrimination and an excellent overall diastereoselectivity. Whereas the “subcatalyst” (hidden catalyst) is not present in the reaction’s initial components, which renders a chiral catalyst-free process, it is strategically produced to promote sequential self-catalyzed reactions. The success of this methodology will pave the way for many efficient preparations of chiral complex molecules and aid for the quest to create next generation of therapeutic agents.</p>

Visible Light-Mediated Oxidative Debenzylation

2020 ◽  
Author(s):  
Cristian Cavedon ◽  
Eric T. Sletten ◽  
Amiera Madani ◽  
Olaf Niemeyer ◽  
Peter H. Seeberger ◽  
...  
Keyword(s):  
Reaction Time ◽  
Visible Light ◽  
Functional Groups ◽  
Continuous Flow ◽  
Protecting Groups ◽  
Benzyl Ether ◽  
Complex Molecules ◽  
Protective Groups ◽  
Benzyl Ethers ◽  
Harsh Conditions

Protecting groups are key in the synthesis of complex molecules such as carbohydrates to distinguish functional groups of similar reactivity. The harsh conditions required to cleave stable benzyl ether protective groups are not compatible with many other protective and functional groups. The mild, visible light-mediated debenzylation disclosed here renders benzyl ethers orthogonal protective groups. Key to success is the use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as stoichiometric or catalytic photooxidant such that benzyl ethers can be cleaved in the presence of azides, alkenes, and alkynes. The reaction time for this transformation can be reduced from hours to minutes in continuous flow. <br>

Three-Component [1+1+1] Cyclopropanation with Ruthenium(II)

2018 ◽  
Author(s):  
Tanner C. Jankins ◽  
Robert R. Fayzullin ◽  
Eugene Khaskin
Keyword(s):  
Quaternary Carbon ◽  
Poor Control ◽  
One Step ◽  
Synthetic Routes ◽  
Mechanistic Investigations ◽  
Chiral Centers ◽  
Metal Catalyzed ◽  
The Right ◽  
Substituted Cyclopropanes

We report a one-step, Ru(II)-catalyzed cyclopropanation reaction that is conceptually different from the previously reported protocols that include Corey-Chaykovsky, Simmons-Smith, and metal catalyzed carbene attack on olefins. Under the current protocol, various alcohols are transformed into sulfone substituted cyclopropanes with excellent isolated yields and diastereoselectivities. This new reaction forms highly congested cyclopropane products with three new C–C bonds, three or two new chiral centers and one new quaternary carbon center. 22 examples of isolated substrates are given. Previously reported synthetic routes for similar substrates are all multi-step, linear routes that proceed with overall low yields and poor control of stereochemistry. Experimental mechanistic investigations suggest initial metal-catalyzed dehydrogenation of the alcohol substrate and catalyst independent stepwise attack of two equivalents of sulfone on the aldehyde under basic conditions. While the Ru(II) is only responsible for the initial dehydrogenation step, the rate of aldehyde formation is crucial to maintaining the right balance of intermediates needed to afford the cyclopropane product.

Medicinal Chemistry Database GDBMedChem

2019 ◽  
Author(s):  
Mahendra Awale ◽  
Finton Sirockin ◽  
Nikolaus Stiefl ◽  
Jean-Louis Reymond
Keyword(s):  
Small Molecules ◽  
Natural Product ◽  
Medicinal Chemistry ◽  
3D Visualization ◽  
Molecular Size ◽  
Similarity Searching ◽  
Complex Molecules ◽  
Synthetic Accessibility ◽  
Simple Chemical ◽  
Reduced Complexity

<div>The generated database GDB17 enumerates 166.4 billion possible molecules up to 17 atoms of C, N, O, S and halogens following simple chemical stability and synthetic feasibility rules, however medicinal chemistry criteria are not taken into account. Here we applied rules inspired by medicinal chemistry to exclude problematic functional groups and complex molecules from GDB17, and sampled the resulting subset evenly across molecular size, stereochemistry and polarity to form GDBMedChem as a compact collection of 10 million small molecules.</div><div><br></div><div>This collection has reduced complexity and better synthetic accessibility than the entire GDB17 but retains higher sp 3 - carbon fraction and natural product likeness scores compared to known drugs. GDBMedChem molecules are more diverse and very different from known molecules in terms of substructures and represent an unprecedented source of diversity for drug design. GDBMedChem is available for 3D-visualization, similarity searching and for download at http://gdb.unibe.ch.</div>

Metal-Free Photoredox-Catalyzed C–H/C–H Coupling of Arenes Enabled by Interrupted Pummerer Activation

2019 ◽  
Author(s):  
Miles Aukland ◽  
Mindaugas Šiaučiulis ◽  
Adam West ◽  
Gregory Perry ◽  
David Procter
Keyword(s):  
Natural Product ◽  
Selective Reduction ◽  
Cross Coupling ◽  
One Pot ◽  
Complex Molecules ◽  
Pummerer Reaction ◽  
Metal Free ◽  
Bond Forming ◽  
Coupling Partner ◽  
Bioactive Natural Product

<p>Aryl–aryl cross-coupling constitutes one of the most widely used procedures for the synthesis of high-value materials, ranging from pharmaceuticals to organic electronics and conducting polymers. The assembly of (hetero)biaryl scaffolds generally requires multiple steps; coupling partners must be functionalized before the key bond-forming event is considered. Thus, the development of selective C–H arylation processes in arenes, that side-step the need for prefunctionalized partners, is crucial for streamlining the construction of these key architectures. Here we report an expedient, one-pot assembly of (hetero)biaryl motifs using photocatalysis and two non-prefunctionalized arene partners. The approach is underpinned by the activation of a C–H bond in an arene coupling partner using the interrupted Pummerer reaction. A unique pairing of the organic photoredox catalyst and the intermediate dibenzothiophenium salts enables highly selective reduction in the presence of sensitive functionalities. The utility of the metal-free, one-pot strategy is exemplified by the synthesis of a bioactive natural product and the modification of complex molecules of societal importance.</p>

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