Site- and Stereoselective C–H Alkylations of Carbohydrates Enabled by Cooperative Photoredox, Hydrogen Atom Transfer, and Organotin Catalysis
作者:Daniel J. Gorelik、Julia A. Turner、Tarunpreet S. Virk、Daniel A. Foucher、Mark S. Taylor
DOI:10.1021/acs.orglett.1c01718
日期:2021.7.2
carbohydrates with electron-deficientalkenes in the presence of an Ir(III) photoredox catalyst and quinuclidine, a hydrogen atom transfer mediator. Quantum-chemical calculations support a proposed mechanism involving the formation of a cyclic stannylene acetal intermediate that shows enhanced reactivity toward hydrogen atom abstraction by the quinuclidinium radical cation. Addition of the carbon-centered
Photocatalytic, site-selective oxidations of carbohydrates
作者:Daniel J. Gorelik、Victoria Dimakos、Timur Adrianov、Mark S. Taylor
DOI:10.1039/d1cc05124e
日期:——
Site-selective oxidations of carbohydrates, employing acridinium photocatalysis and quinuclidine hydrogen atom transfer catalysis, are presented. Protocols have been developed for oxidations of all-equatorial carbohydrates as well as those containing cis-1,2-diols. Site-selectivity reflects the relative rates of hydrogen atom transfer from the carbohydrate C–H bonds, and can be enhanced using a phosphate
Synthesis of Tri-, Hexa-, and Nonasaccharide Subunits of the Atypical O-Antigen Polysaccharide of the Lipopolysaccharide from Danish <i>Helicobacter </i><i>pylori</i> Strains
作者:Dinanath Baburao Fulse、Heung Bae Jeon、Kwan Soo Kim
DOI:10.1021/jo701531x
日期:2007.12.1
Synthesis of trisaccharide repeating unit, -> 3)-alpha-D-Rhap-(1 -> 2)-alpha-D-Manp3CMe-(1 -> 3)-alpha-L-Rha p-(1 ->, and its dimeric hexa- and trimeric nonasaccharide subunits of the atypical O-antigen polysaccharide of the lipopolysaccharide from Danish H. pylori strains D1, D3, and D6 has been accomplished. Successful synthesis of the hexasaccharide and the nonasaccharide was possible by dimerization and trimerization of the suitably protected trisaccharide repeating unit, in which three monosaccharide moieties were arranged in a proper order by placing the sterically demanding 3-C-methyl-D-mannose moiety in between D- and L-rhamnoses. Key steps include the coupling of three monosaccharide moieties and dimerization and trimerization of the trisaccharide unit by glycosylations employing the 2'-carboxybenzyl glycoside method.. Also presented is a method for the synthesis of the novel branched sugar, 3-C-methyl-D-mannose moiety by elaboration of its equatorial hydroxyl and axial methyl groups at C-3' in the disaccharide stage.