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Achim Link, Christof Sparr
While aromatic hydrocarbons are ubiquitous in organic chemistry, they are typically not associated with chirality and stereoisomerism. Due to the planarity and symmetry of simple arenes, methods to assemble aromatic rings are not routinely considered for the stereoselective synthesis of chiral compounds. The aim of this tutorial review is to contrast this common perception with the counterintuitive circumstance that stereoselective arene formation offers a means to stereoselectively prepare an exceptional range of chiral aromatic structures...
March 22, 2018: Chemical Society Reviews
Sarah E Wilkins, Saiful Islam, Joan M Gannon, Suzana Markolovic, Richard J Hopkinson, Wei Ge, Christopher J Schofield, Rasheduzzaman Chowdhury
Oxygenase-catalysed post-translational modifications of basic protein residues, including lysyl hydroxylations and Nε -methyl lysyl demethylations, have important cellular roles. Jumonji-C (JmjC) domain-containing protein 5 (JMJD5), which genetic studies reveal is essential in animal development, is reported as a histone Nε -methyl lysine demethylase (KDM). Here we report how extensive screening with peptides based on JMJD5 interacting proteins led to the finding that JMJD5 catalyses stereoselective C-3 hydroxylation of arginine residues in sequences from human regulator of chromosome condensation domain-containing protein 1 (RCCD1) and ribosomal protein S6 (RPS6)...
March 21, 2018: Nature Communications
Sophie L Mader, Alois Bräuer, Michael Groll, Ville R I Kaila
The recently discovered FeII /α-ketoglutarate-dependent dioxygenase AsqJ from Aspergillus nidulans stereoselectively catalyzes a multistep synthesis of quinolone alkaloids, natural products with significant biomedical applications. To probe molecular mechanisms of this elusive catalytic process, we combine here multi-scale quantum and classical molecular simulations with X-ray crystallography, and in vitro biochemical activity studies. We discover that methylation of the substrate is essential for the activity of AsqJ, establishing molecular strain that fine-tunes π-stacking interactions within the active site...
March 21, 2018: Nature Communications
Ciro Romano, Clément Mazet
Starting from readily available alkenyl methyl ethers, the stereoselective preparation of highly substituted alkenes by two complementary multicatalytic sequential isomerization/cross-coupling sequences is described. Both elementary steps of these sequences are challenging processes when considered independently. A cationic iridium catalyst was identified for the stereoselective isomerization of allyl methyl ethers and was found to be compatible with a nickel catalyst for the subsequent cross-coupling of the in situ generated methyl vinyl ethers with various Grignard reagents...
March 21, 2018: Journal of the American Chemical Society
Jung Tae Han, Jaesook Yun
An efficient, catalytic method for accessing tetrasubstituted enynylboronates has been established via copper-catalyzed chemo-, regio-, and stereoselective borylalkynylation of internal alkynes. In this protocol, a range of symmetrical and unsymmetrical internal alkynes with aryl, heteroaryl, and alkyl substituents afforded fully substituted enynylboron compounds in good yields and with high levels of regio- and stereoselectivity, up to a ratio of >20:1. The enynylboron products could be further utilized in transforming the C-B bond into C-C bonds by coupling reactions...
March 21, 2018: Organic Letters
Xin Fang, Chun-Jiang Wang
Spirocyclic pyrrolidines are structural motifs frequently found in a wide variety of natural products, pharmaceuticals and biologically significant compounds. In the past few years, catalytic asymmetric 1,3-dipolar cycloaddition reactions of azomethine ylides have shown to be one of the most straightforward methods for the stereoselective preparation of diverse biologically important spiropyrrolidine heterocycles in high yields with excellent enantioselectivities under mild reaction conditions. In this review, we will discuss the recent major developments in the catalytic enantioselective synthesis of chiral spiropyrrolidine derivatives since 2009...
March 21, 2018: Organic & Biomolecular Chemistry
Andrea Gandini, Ahmed A Amin, Hawraz Ibrahim M Amin, Davide Corriero, Alessio Porta, Giuseppe Zanoni
A practical methodology for the synthesis of key intermediates for isoprostane, neuroprostane and dihomo-isoprostane preparation has been described. The key strategy involved a three stage C-12 stereocenter inversion of the configuration of a Corey lactone, commercially available in an enantiopure form. The key intermediate was then used to prepare 17-E2c-dihomo-isoprostane and 17-F2c-dihomo-isoprostane.
March 21, 2018: Organic & Biomolecular Chemistry
Guoxian Gu, Jiaxiang Lu, Ouran Yu, Jialin Wen, Qin Yin, Xumu Zhang
An iridium/f-amphol catalytic system for the enantioselective hydrogenation of α-substituted β-ketoesters via dynamic kinetic resolution is reported. The desired anti products were obtained in high yields (up to 98%) with good diastereoselectivity (up to 96:4 diastereometic ratio (dr)) and excellent enantioselectivity (up to >99% enantiomeric excess (ee)). A catalytic model is proposed to explain the stereoselectivity.
March 20, 2018: Organic Letters
Zhi-Min Li, Ya-Wei Li, Xiao-Ping Cao, Hak-Fun Chow, Dietmar Kuck
A new chiral tribenzotriquinacene bearing an ortho-bromoaniline nucleus was synthesized and optically resolved. The individual enantiomers, the absolute configuration of which was confirmed by single crystal X-ray structure analysis, were stereoselectively converted into the same pyrazine-fused syn-bis-TBTQ derivative by chirality-assisted Buchwald-Hartwig amination. The corresponding diastereomeric anti-dimer was obtained alongside with the syn-dimer from the racemic sample under similar reaction conditions...
March 19, 2018: Journal of Organic Chemistry
Xiaojing Liu, Junhao Jia, Yuanliang Jia, He Gu, Jingwen Luo, Xiaochuan Chen
A flexible strategy has been developed to synthesize divergent flavonoids bearing a chiral A-ring. As two key steps, the coupling via a boron-mediated aldol condensation and the cyclization via a highly stereoselective intramolecular Michael addition of 1,3-diketone proceed under mild conditions; thus, the chiral flavonoids bearing C-7 oxy functional groups or olefinic bonds are both easily accessible. Using this approach, the first synthesis of (+)-cryptogione F, (+)-cryptocaryanone B, and (+)-cryptochinones A and C, as well as stereoselective synthesis of (+)-cryptocaryone and (+)-cryptocaryanone A, were achieved from 2-deoxy-d-ribose in high overall yields...
March 19, 2018: Organic Letters
Liming Wang, Herman S Overkleeft, Gijsbert A van der Marel, Jeroen D C Codée
The development of a general glycosylation method that allows for the stereoselective construction of glycosidic linkages is a tremendous challenge. Because of the differences in steric and electronic properties of the building blocks used the outcome of a glycosylation reaction can greatly vary when switching form one glycosyl donor-acceptor pair to another. We here report a strategy to install cis-glucosidic linkages in a fully stereoselective fashion that is under direct control of the reagents used to activate a singly type of donor building block...
March 19, 2018: Journal of the American Chemical Society
Wenbin Shao, Jun Huang, Kai Guo, Jianxian Gong, Zhen Yang
The total synthesis of naturally occurring (±)-sinensilactam A was achieved in 18 steps. The key steps of this work are a rhodium-catalyzed [3 + 2] cycloaddition for construction of the two all-carbon vicinal quaternary centers and a convergent and tandem condensation of the in situ generated N-acyliminium intermediate with aldehyde 20. This enabled implementation of a unified strategy for stereoselective formation of the tetracyclic hemiaminal core of sinensilactam A in a later stage. The total syntheses of applanatumol F and C8- epi-applanatumol D are also achieved using this strategy...
March 19, 2018: Organic Letters
Ling Yang, Wei-Wei Ji, E Lin, Ji-Lin Li, Wen-Xin Fan, Qingjiang Li, Honggen Wang
A reductive cross-coupling of gem-difluoroalkenes with diverse unactivated and heteroatom substituted olefins through a Fe-catalyzed hydrogen atom transfer (HAT) strategy is reported. Different from the previous HAT-type olefin cross-coupling reactions, the presence of a fluorine atom in the molecule results in a stereoselective β-F cleavage, leading to a C(sp2 )-C(sp3 ) bond formation. A wide variety of alkylated monofluoroalkenes were obtained in good efficiency with excellent Z selectivity under air- and water-tolerant reaction conditions...
March 19, 2018: Organic Letters
Lech-Gustav Milroy, Bartjan Koning, Daphne S V Scheppingen, Nynke G L Jager, Jos H Beijnen, Jan Koek, Luc Brunsveld
Z-Endoxifen is widely regarded as the most active metabolite of tamoxifen, and has recently demonstrated a 26.3% clinical benefit in a phase I clinical trial to treat metastatic breast cancer after the failure of standard endocrine therapy. Future pharmacological and pre-clinical studies of Z-endoxifen would benefit from reliable and efficient synthetic access to the drug. Here, we describe a short and efficient, stereoselective synthesis of Z-endoxifen capable of delivering multi-gram (37 g) quantities of the drug in >97% purity with a Z/E ratio >99% after trituration...
March 13, 2018: Bioorganic & Medicinal Chemistry Letters
Christopher Ryan Shugrue, Aaron L Featherston, Rachel M Lackner, Angela Lin, Scott J Miller
Phosphothreonine (pThr)-embedded peptide catalysts are found to mediate the reductive amination of 3-amidocyclohexanones with divergent selectivity. Choice of peptide sequence can be used to alter the diastereoselectivity to favor either cis-product or trans-product, which are obtained in up to 93:7 er. NMR studies and DFT calculations are reported and indicate that both pathways rely on secondary interactions between substrate and catalyst to achieve selectivity. Furthermore, catalysts appear to accomplish a parallel kinetic resolution of the substrates...
March 16, 2018: Journal of Organic Chemistry
Masao Morita, Yuichi Kobayashi
The stereoselective synthesis of resolvin D4 (RvD4) was achieved using the Wittig reaction of the C1-C10 dienal with the known C11-C22 phosphonium salt. The (S,E)-enantiomer (S)-10, corresponding to the C1-C8 part, was synthesized in 95% ee by the asymmetric transfer hydrogenation reaction of the corresponding acetylenic ketone followed by Red-Al reduction. Sharpless epoxidation of this alcohol using Ti(O-i-Pr)4/L-(+)-DIPT as a catalyst produced anti epoxy alcohol with >99% ee as the sole product in 82% yield...
March 16, 2018: Journal of Organic Chemistry
Manisha B Walunj, Arun A Tanpure, Seergazhi G Srivatsan
Pd-catalyzed C-C bond formation, an important vertebra in the spine of synthetic chemistry, is emerging as a valuable chemoselective transformation for post-synthetic functionalization of biomacromolecules. While methods are available for labeling protein and DNA, development of an analogous procedure to label RNA by cross-coupling reactions remains a major challenge. Herein, we describe a new Pd-mediated RNA oligonucleotide (ON) labeling method that involves post-transcriptional functionalization of iodouridine-labeled RNA transcripts by using Suzuki-Miyaura cross-coupling reaction...
March 13, 2018: Nucleic Acids Research
Jian-Biao Liu, Ying-Ying Tian, Xin Zhang, Lu-Lin Wang, De-Zhan Chen
The detailed mechanism of palladium-catalyzed γ-C(sp3)-H olefination/cyclization of triflyl-protected amines was investigated by density functional theory (DFT) calculations. The olefinated intermediate was initially formed in the first catalytic cycle involving ligand exchange, bicarbonate-assisted C(sp3)-H bond cleavage, alkene insertion and 'reductive β-hydride elimination'. The following syn-addition and reductive elimination furnish the aza-Wacker product. The first step of reductive elimination is the rate-determining step...
March 16, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Lucas W Hernandez, Ulrich Klöckner, Jola Pospech, Lilian Hauss, David Sarlah
We describe the development of an arenophile-mediated, nickel-catalyzed dearomative trans-1,2-carboamination protocol. A range of readily available aromatic compounds was converted to the corresponding dienes using Grignard reagents as nucleophiles. This strategy provided products with exclusive trans-selectivity and high enantioselectivity was observed in case of benzene and naphthalene. The utility of this methodology was showcased by controlled and stereoselective preparation of small, functionalized molecules...
March 15, 2018: Journal of the American Chemical Society
Boris A Trofimov, Pavel A Volkov, Kseniya O Khrapova, Anton A Telezhkin, Nina I Ivanova, Alexander I Albanov, Nina K Gusarova, Oleg N Chupakhin
Pyridines undergo site selective cross-coupling with secondary phosphine chalcogenides (oxides, sulfides, and selenides) in the presence of acylphenylacetylenes under metal-free mild conditions (70-75 °C, MeCN) to afford 4-chalcogenophosphoryl pyridines in up to 71% yield. In this new type of SNHAr reaction acylacetylenes act as oxidants, being stereoselectively reduced to the corresponding olefins of the E-configuration.
March 15, 2018: Chemical Communications: Chem Comm
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