title: The isothiocyanato moiety: an ideal protecting group for the stereoselective synthesis of sialic acid glycosides and subsequent diversification.
abstract: The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at -78 °C in the presence of typical carbohydrate acceptors, this donor gives high yields of the corresponding sialosides with exquisite α-selectivity. The high selectivity extends to the 4-O-benzyl-protected 3-OH acceptors, which are typically less reactive and selective than galactose 3,4-diols. Treatment of the α-sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane results in replacement of the C5-N5 bond by a C-H or a C-C bond. The reaction of the isothiocyanate-protected sialosides with thioacids generates amides, while reaction with an amine gives a thiourea, which can be converted into a guanidine. The very high α-selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5-position.
authors.affiliation: Department of Chemistry, Wayne State University, Detroit, MI 48202 (USA) http://chem.wayne.edu/crichgroup.
authors.forename: Appi Reddy
authors.initials: AR
authors.lastname: Mandhapati
authors.forename: Salla
authors.initials: S
authors.lastname: Rajender
authors.forename: Jonathan
authors.initials: J
authors.lastname: Shaw
authors.forename: David
authors.initials: D
authors.lastname: Crich
mesh_terms: D003641:Deamination; D006027:Glycosides / Q000138:chemical synthesis* / Q000737:chemistry; D019791:Guanidine / Q000737:chemistry; D019158:N-Acetylneuraminic Acid / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry; D013237:Stereoisomerism; D013861:Thiocyanates / Q000737:chemistry*; D013890:Thiourea / Q000737:chemistry
chemical_list: D006027:Glycosides; D012821:Silanes; D013861:Thiocyanates; D013890:Thiourea; D019158:N-Acetylneuraminic Acid; D019791:Guanidine; C031760:thiocyanate
keywords: deamination; glycosylation; guanidine; isothiocyanate; thiourea