- Epimerization of glycal derivatives by a cyclopentadienylruthenium catalyst: Application to metalloenzymatic DYKAT
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Epimerization of a non-anomeric stereogenic center in carbohydrates is an important transformation in the synthesis of natural products. In this study an epimerization procedure of the allylic alcohols of glycals by cyclopentadienylruthenium catalyst 1 is presented. The epimerization of 4,6-O-benzylidene-d-glucal 4 in toluene is rapid, and an equlibrium with its d-allal epimer 5 is established within 5 min at room temperature. Exchange rates for allal and glucal formation were determined by 1D 1H EXSY NMR experiments to be 0.055 s-1 and 0.075 s -1, respectively. For 4-O-benzyl-l-rhamnal 8 the epimerization was less rapid and four days of epimerization was required to achieve equilibration of the epimers at room temperature. The epimerization methodology was subsequently combined with acylating enzymes in a dynamic kinetic asymmetric transformation (DYKAT), giving stereoselective acylation to the desired stereoisomers 12, 13 , and 15. The net effect of this process is an inversion of a stereogenic center on the glycal, and yields ranging from 71% to 83% of the epimer were obtained.
- Lihammar, Richard,R?nnols, Jerk,Widmalm, G?ran,B?ckvall, Jan-E.
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p. 14756 - 14762
(2015/04/16)
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- A facile synthesis of 4,6-O-benzylidene-d-glycals via 1,5-anhydro-4,6-O-benzylidene-d-hex-1-en-3-ulose
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Benzylidenation of readily available 1,5-anhydro-d-hex-1-en-3-ulose, followed by sodium borohydride reduction, afforded the title compounds in high yields. Separation of 4,6-O-benzylidene-d-allal and -d-glucal was accomplished by selective acetylation wit
- Sakakibara, Tohru,Ito, Tsubasa,Kotaka, Chika,Kajihara, Yasuhiro,Watanabe, Yuhya,Fujioka, Aki
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experimental part
p. 2740 - 2743
(2009/04/11)
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- The total synthesis of allosamidin. Expansions of the methodology of azaglycosylation pursuant to the total synthesis of allosamidin. A surprising enantiotopic sense for a lipase-induced deacetylation
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Allosamidin, recently isolated from mycelial extracts of Streptomyces sp. 1713, is a powerful and selective chitinase inhibitor. The total synthesis of allosamidin is described herein. The electric eel acetylcholinesterase-mediated enantioselective hydrolysis of (trans,trans)-2-(benzyloxy)cyclopentene-1,3-diol diacetate accessed a monoacetyl derivative. Five additional steps produced a protected version of the aglycon ('allosamizoline') sector of allosamidin. An allal derivative stereoselectively reacted with benzenesulfonamide in the presence of a halonium source to afford a 2β-halo-1α-sulfonamidohexose. Treatment of this product with a strong base generated an intermediate 1,2-sulfonylaziridine, which was trapped with a protected allal derivative to provide a disaccharide glycal. Reiteration of this scheme gave access to the required trisaccharide. Following deprotection, the total synthesis of allosamidin was accomplished. In addition, the method, with modification, gave access to several allosamidin analogs.
- Griffith, David A.,Danishefsky, Samuel J.
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p. 9526 - 9538
(2007/10/03)
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- Allylic Nucleophilic Substitution Reactions in Sugars. III. Uncatalysed Displacements in Hexamethylphosphoramide
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The uncatalysed displacement of allylic benzoyloxy groups with azide in unsaturated sugars has been studied by using hexamethylphosphoramide as solvent.Tri-O-benzoylglycals and 4,6-O-benzylidene-3-O-benzoylglycals were investigated.The former gave rise to
- Guthrie, R. D. (Gus),Irvine, Robert W.,Jenkins, Ian D.
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p. 2499 - 2508
(2007/10/02)
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- ALLYLIC SUBSTITUTIONS IN TRI-O-BENZYL-GLYCALS, 4,6-OBENZYLIDENE-GLYCALS AND RELATED COMPOUNDS
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3,4,6-Tri-O-benzyl-D-glucal and the benzyl 4,6-di-O-benzyl-2,3-dideoxy-hex-2-enopyranosides react with sodium azide in acetonitrile under boron trifluoride catalysis to yield mixtures of 3-azido-glycals and 2,3-unsaturated glycosyl azides.Similar reaction
- Guthrie, R. D. (Gus),Irvine, Robert W.
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p. 225 - 236
(2007/10/02)
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