343 research outputs found

    Straightforward Synthesis of α,β-Unsaturated Thioesters via Ruthenium-Catalyzed Olefin Cross-Metathesis with Thioacrylate

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    The cross-metathesis reaction of S-ethyl thioacrylate with a variety of olefins is effectively catalyzed by using a ruthenium benzylidene olefin metathesis catalyst. This reaction provides a convenient and versatile route to substituted α,β-unsaturated thioesters, key building blocks in organic synthesis.

    Racemic Total Synthesis of Elmonin and Pratenone A, from Streptomyces, Using a Common Intermediate Prepared by peri-Directed C-H Functionalization

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    [Image: see text] The first total synthesis of elmonin and pratenone A, two complex rearranged angucyclinones from Streptomyces, is reported. Using peri-directed C–H functionalization, the key naphthalene fragment present in both synthetic targets was efficiently prepared. Coupling to two anisole-derived fragments gave access to the natural products, in which elmonin was prepared using a biomimetic spiro-ketalization

    Formal Synthesis of the Anti-Angiogenic Polyketide (-)-Borrelidin under Asymmetric Catalytic Control

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    Borrelidin (1) is a polyketide that possesses extremely potent anti-angiogenesis activity. This paper describes its formal total synthesis by the most efficient route to date. This modular approach takes optimal benefit of asymmetric catalysis and permits the synthesis of analogues; in addition, the high yields and selectivities obtained eliminate the need for separation of stereoisomers. The upper half of borrelidin has been accessed by iterative copper-catalysed asymmetric conjugate addition of methylmagnesium bromide, whereas synthesis of the lower half of the molecule was achieved by relying on asymmetric hydrogenation and cross-methathesis as key steps

    Chemical Synthesis of Cell Wall Constituents of Mycobacterium tuberculosis

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    The pathogen Mycobacterium tuberculosis (Mtb), causing tuberculosis disease, features an extraordinary thick cell envelope, rich in Mtb-specific lipids, glycolipids, and glycans. These cell wall components are often directly involved in host-pathogen interaction and recognition, intracellular survival, and virulence. For decades, these mycobacterial natural products have been of great interest for immunology and synthetic chemistry alike, due to their complex molecular structure and the biological functions arising from it. The synthesis of many of these constituents has been achieved and aided the elucidation of their function by utilizing the synthetic material to study Mtb immunology. This review summarizes the synthetic efforts of a quarter century of total synthesis and highlights how the synthesis layed the foundation for immunological studies as well as drove the field of organic synthesis and catalysis to efficiently access these complex natural products

    Synthesis of Optically Active Bifunctional Building Blocks through Enantioselective Copper-Catalyzed Allylic Alkylation Using Grignard Reagents

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    Enantioselective copper-catalyzed allylic alkylations were performed on allylic bromides with a protected hydroxyl or amine functional group using several Grignard reagents and Taniaphos L1 as a ligand. The terminal olefin moiety in the products was transformed into various functional groups without racemization, providing facile access to a variety of versatile bifunctional chiral building blocks.

    Site-selective introduction of thiols in unprotected glycosides

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    Thioglycosides or S-linked-glycosides are important glycomimetics. These thioglycosides are often prepared by glycosylating deoxythio sugar acceptors, which are synthesized via elaborate protecting group manipulations. We discovered that a carbonyl group, formed by site-selective oxidation of unprotected saccharides, can be converted into a thiol moiety. The transformation involves SN1-substitution of a chloro-azo intermediate, formed by oxidation of the corresponding trityl hydrazone, with a thiol. The prepared deoxythio sugars provide, in combination with the recently developed protecting group-free glycosylation of glycosyl fluorides, a protecting group-free synthesis of thioglycosides.</p

    Synthesis of phosphatidic acids via cobalt(salen) catalyzed epoxide ring-opening with dibenzyl phosphate

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    With a CoIII(salen)OTs catalyst, dibenzyl phosphate ring-opens a variety of terminal epoxides with excellent regio-selectively and yields up to 85%. The reaction is used in a highly efficient synthesis of enantiopure mixed-diacyl phosphatidic acids, including a photoswitchable phosphatidic acid mimic

    Potential Modulatory Microbiome Therapies for Prevention or Treatment of Inflammatory Bowel Diseases

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    A disturbed interaction between the gut microbiota and the mucosal immune system plays a pivotal role in the development of inflammatory bowel disease (IBD). Various compounds that are produced by the gut microbiota, from its metabolism of diverse dietary sources, have been found to possess anti-inflammatory and anti-oxidative properties in in vitro and in vivo models relevant to IBD. These gut microbiota-derived metabolites may have similar, or more potent gut homeostasis-promoting effects compared to the widely-studied short-chain fatty acids (SCFAs). Available data suggest that mainly members of the Firmicutes are responsible for producing metabolites with the aforementioned effects, a phylum that is generally underrepresented in the microbiota of IBD patients. Further efforts aiming at characterizing such metabolites and examining their properties may help to develop novel modulatory microbiome therapies to treat or prevent IBD

    From d- to l-Monosaccharide Derivatives via Photodecarboxylation-Alkylation

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    Photodecarboxylation-alkylation of conformationally locked monosaccharides leads to inversion of stereochemistry at C5. This allows the synthesis of l-sugars from their readily available d-counterparts. Via this strategy, methyl l-guloside was synthesized from methyl d-mannoside in 21% yield over six steps

    Chiral separation by enantioselective liquid–liquid extraction

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    The literature on enantioselective liquid–liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid–liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid–liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid–liquid extraction including host–guest chemistry, extraction and phase transfer mechanisms, and multistage liquid–liquid extraction processing. Then the literature on enantioselective liquid–liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants.
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