title: O-sialylation with N-acetyl-5-n,4-o-carbonyl-protected thiosialoside donors in dichloromethane: facile and selective cleavage of the oxazolidinone ring.
abstract: An N-acetyl-5-N,4-O-carbonyl-protected thiosialoside donor, the structure of which has been defined through X-ray crystallography, was prepared and tested in couplings to a wide range of acceptors. This donor gives excellent yields and alpha-selectivities in linking with various primary alkyl and carbohydrate acceptors under the N-iodosuccinimide and trifluoromethanesulfonic acid in situ activation method at -40 degrees C in dichloromethane. The favorable affect of the oxazolidinone substructure for alpha-sialylation is illustrated by a comparison study with a N,N-diacetylsialyl donor, which exhibited inferior yields and alpha-selectivities. The sialylation selectivity is independent of the anomeric configuration of the donor, but is highly related to the reaction temperature under the NIS/TfOH activation method. In contrast to the NIS/TfOH method, the Ph2SO/Tf2O promotion gives beta-selective couplings in dichloromethane. The oxazolidinone of the N-acetyl-5-N,4-O-carbonyl protected sialosides, both alpha- and beta-anomers, could be cleaved cleanly by treatment with sodium methoxide under mild conditions without removal of the acetamide.
authors.affiliation: Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA. dcrich@uic.edu
authors.forename: David
authors.initials: D
authors.lastname: Crich
authors.forename: Wenju
authors.initials: W
authors.lastname: Li
mesh_terms: D000107:Acetylation; D005663:Furans / Q000737:chemistry*; D005732:Gangliosides / Q000737:chemistry*; D008737:Methyl Chloride / Q000737:chemistry*; D015394:Molecular Structure; D019158:N-Acetylneuraminic Acid / Q000737:chemistry*; D023303:Oxazolidinones / Q000737:chemistry*
chemical_list: D005663:Furans; D005732:Gangliosides; D023303:Oxazolidinones; D008737:Methyl Chloride; D019158:N-Acetylneuraminic Acid