@article{ZehmFudickarHansetal.2008, author = {Zehm, Daniel and Fudickar, Werner and Hans, Melanie and Schilde, Uwe and Kelling, Alexandra and Linker, Torsten}, title = {9,10-Diarylanthracenes as molecular switches : syntheses, properties, isomerisations and their reactions with singlet oxygen}, issn = {0947-6539}, year = {2008}, abstract = {A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl-aryl axis commences at <100 °C for fluoro-substituted diarylanthracenes and at >300 °C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl-aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step.}, language = {en} } @article{YinLinker2009, author = {Yin, Jian and Linker, Torsten}, title = {Convenient synthesis of bicyclic carbohydrate 1,2-lactones and their stereoselective opening to 1- functionalized glucose derivatives}, issn = {0947-6539}, doi = {10.1002/chem.200802178}, year = {2009}, abstract = {Closed and re-opened for business: C-2 branched carbohydrates 1 cyclize under conditions of decarboxylation to the hitherto unknown carbohydrate 1,2-lactones 2 in high yields. The gluco isomer can be opened at the anomeric position with various nuceophiles in the presence of Sc(OTf)3, which allows the stereoselective synthesis of 1-functionalized glucose derivatives 3. Thus, 1,2-bis-C-branched saccharides become available in only a few steps starting from glycals.}, language = {en} } @article{YinLinker2009, author = {Yin, Jian and Linker, Torsten}, title = {Stereodivergent syntheses at the glucose backbone}, issn = {1477-0520}, doi = {10.1039/B918893m}, year = {2009}, abstract = {Both diastereomers of 2-C-branched carbohydrates with various functional groups are selectively available from the same malonate precursor in good yields in only a few steps.}, language = {en} } @article{YinLinker2011, author = {Yin, Jian and Linker, Torsten}, title = {Stereoselective diversity-oriented syntheses of functionalized saccharides from bicyclic carbohydrate 1,2-lactones}, series = {Tetrahedron}, volume = {67}, journal = {Tetrahedron}, number = {13}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2011.01.069}, pages = {2447 -- 2461}, year = {2011}, abstract = {Bicyclic carbohydrate 1,2-lactones have been synthesized in only two steps and high yields by saponification and subsequent cyclization from known malonate addition products to glycals. The gluco-configured lactone serves as an important precursor for diversity-oriented syntheses. Thus, stereoselective opening of the lactone ring was realized with various nucleophiles in the presence of Sc(OTf)(3). This enabled the introduction of different substituents at the anomeric position, to afford a broad variety of 1-functionalized carbohydrates. On the other hand, stereoselective alpha-substitution of the gluco-configured lactone with different electrophiles and subsequent ring opening gives a collection of 2-functionalized saccharides. More than 30 products have been isolated in analytically pure form, and their configurations were unequivocally established by various NMR methods. Thus, carbohydrate 1,2-lactones are attractive precursors for the stereoselective synthesis of diverse saccharides.}, language = {en} } @article{YinLinker2012, author = {Yin, Jian and Linker, Torsten}, title = {Recent advances in the stereoselective synthesis of carbohydrate 2-C-analogs}, series = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, volume = {10}, journal = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, number = {12}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-0520}, doi = {10.1039/c2ob06529k}, pages = {2351 -- 2362}, year = {2012}, abstract = {C-branched carbohydrates are of current interest for glycochemistry, are widely found in nature and serve as important subunits in many antibiotics, bacterial polysaccharides and macrolides. Among C-functionalized saccharides, 2-C-branched carbohydrates represent challenging structures for synthetic chemists, since in contrast to C-glycosides they are not easily accessible from glycosyl bromides or other simple precursors. In this perspective we want to summarize recent approaches to 2-C-branched carbohydrates over the past fifteen years. The two main strategies are based on ring-opening of 1,2-cyclopropanated carbohydrates by various reagents, as well as radical additions to glycals and further transformations, developed in our group. Both methods are characterized by high stereoselectivities and good yields and give access to a broad variety of functionalized carbohydrate 2-C-analogs.}, language = {en} } @article{WangWangHuetal.2015, author = {Wang, Xuebin and Wang, Xiaoli and Hu, Jing and Wang, Zhaoya and Pimpalpalle, Tukaram M. and Linker, Torsten and Yin, Jian}, title = {Study on the Synthesis of Novel Sugar Amino Acids}, series = {Acta chimica Sinica = Huaxue-xuebao}, volume = {73}, journal = {Acta chimica Sinica = Huaxue-xuebao}, number = {7}, publisher = {Science China Press}, address = {Beijing}, issn = {0567-7351}, doi = {10.6023/A15030205}, pages = {699 -- 704}, year = {2015}, abstract = {Sugar amino acids (SAAs) are carbohydrate derivatives bearing both amino and carboxylic acid functional groups. SAAs represent an important class of multifunctional building blocks, which are amenable to serve as glycomimetics or peptidomimetics with well-defined structures and useful properties. Because SAAs exist in nature in many forms with various biological activities, recently, many unnatural SAAs, as the demand for finding new molecules to discover new drugs and new materials, have been designed and synthesized by a number of research groups. In this paper, we have developed a convenient method for the synthesis of novel SAAs gluco-7 and galacto-7 for the first time. The structure of gluco-7 was similar to the natural SAA glucosaminuronic acid that was a component of many typical bacterial cell walls and could be used for the preparation of type D flu vaccine; while galacto-7 was similar to the natural SAA galactosaminuronic acid that was one of bacterial Vi-antigen components of Escherichia coli. Starting from unexpensive and commercially available 3,4,6-tri-O-acetyl-D-glucal and 3,4,6-tri-O-acetyl-D-galactal, two novel SAAs gluco-7 and galacto-7 were achieved in the linear 6 steps with 34\% overall yield and 19\% overall yield, respectively. The key reactions included radical addition, decarboxylation, iodine generation reaction, azide reaction and reductive amination reaction. The crucial step was the synthesis of the target compound gluco-7 from gluco-6. By using method A, the target compound gluco-7 was obtained in 4 steps with 63\% overall yield. To optimize the transformation from gluco-6 to gluco-7, method B was developed to generate gluco-7 by using one-pot reaction successfully with 76\% yield only in one step. It proved that method B was superior to method A with shorter steps and higher yields. All the new compounds were characterized by IR, H-1 NMR, C-13 NMR and HRMS data. Study on the synthesis and biological evaluation of linear and cyclic oligomers derived from gluco-7 and galacto-7 are currently in progress.}, language = {zh} } @article{VorndranLinker2003, author = {Vorndran, Katja Marianne and Linker, Torsten}, title = {Einfache zweistufige ipso-Substitution aromatischer Carbons{\"a}uren durch Alkylhalogenide}, year = {2003}, language = {de} } @article{VorndranLinker2003, author = {Vorndran, Katja Marianne and Linker, Torsten}, title = {Simpla Two-Step ipso Substitution of Aromatic Carboxylic Acids by Alkyl Halides}, issn = {1433-7851}, year = {2003}, language = {en} } @article{VidadalaPimpalpalleLinkeretal.2011, author = {Vidadala, Srinivasa Rao and Pimpalpalle, Tukaram M. and Linker, Torsten and Hotha, Srinivas}, title = {Gold-Catalyzed reactions of 2-C-Branched carbohydrates mild glycosidations and selective anomerizations}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, number = {13}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {1434-193X}, doi = {10.1002/ejoc.201100134}, pages = {2426 -- 2430}, year = {2011}, abstract = {2-C-branched methyl glycosides react with various alcohols under gold catalysis to transglycosylated products. The method is applicable for the convenient synthesis of disaccharides. Without nucleophile a selective anomerization occurs, giving first access to alpha-configured 2-C-nitromethyl glycosides. The results are interesting for the mechanism of gold-catalyzed glycosidations.}, language = {en} } @misc{VankarLinker2015, author = {Vankar, Yashwant D. and Linker, Torsten}, title = {Recent Developments in the Synthesis of 2-C-Branched and 1,2-Annulated Carbohydrates}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, number = {35}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201501176}, pages = {7633 -- 7642}, year = {2015}, abstract = {The importance of carbohydrate chemistry in biological and medicinal chemistry has led to enormous developments in the synthesis of carbohydrate mimics. In this context, the synthesis of branched sugars in general and of 2-C-branched carbohydrates in particular, as well as the synthesis of 1,2-annulated sugars, have received immense attention. They serve not only as carbohydrate mimics in the form of stand-alone molecules, but also as useful intermediates in the synthesis of many natural products, their analogues, and glycosidase inhibitors. This microreview covers the recent synthetic efforts in this area and puts the subject matter into proper perspective for future developments.}, language = {en} }