Use of Acyclic Glycosyl Donors for Furanoside Synthesis

Abstract

Treatment of the peracetylated ethyl dithioacetals of D-glucose, D-galactose, and D-mannose with acetyl chloride and boron trifluoride diethyl etherate at reflux yields the known acyclic 1-chloro-1-(ethylthio) derivatives. These compounds are shown to effectively glycosylate a variety of carbohydrate acceptors using silver trifluoromethanesulfonate as the promotor, affording stereospecifically the corresponding acyclic O,S-acetals in good to excellent yield. Furthermore, following deacetylation, treatment of these O,S-acetals with a mixture of mercuric salts in either methanol or dimethylformamide gives rise to disaccharides terminating in D-furanosyl residues.

Chemical Synthesis of Furanose Glycosides

“…The starting dithioacetals can be easily obtained by treatment of reducing sugars with an excess of thiol and an acid (34). The method, originally described in the 1930ʼs by Green and Pacsu (35), has found increasing use (26,36,37). As originally reported, cyclization involved treatment of the dithioacetal with mercury salts in an alcoholic solvent.…”

“…An alternate approach to furanose glycosides via dithioacetals involves the preparation of O,S-acetals from the dithioacetals (40,41) and subsequent cyclization (42,43). This latter method has been predominantly used to produce furanosides of simple alcohols (42,43), although McAuliffe and Hindsgaul have used it to synthesize disaccharides containing furanose residues (36).…”

“…Regioselective glycosylation of lactone diol 34 with perbenzoate 15 and subsequent acetylation resulted in a 58% yield of disaccharide 35 over the two steps. Reduction of the lactone and then conversion of the resulting hemiacetal (36) to the corresponding trichloroacetimidate (37) generated a donor that could be coupled with hydroxy lactone 38 to give trisaccharide 39 in 75% yield. Trisaccharide 39 is a protected derivative of a motif found in arabinogalactan (AG), a mycobacterial cell wall polysaccharide (8).…”

Synthesis of galactofuranose-containing disaccharides using thioimidoyl-type donors

“…This observation favourably argues for the increasing attention that has been paid to new chemical syntheses of oligofuranosides of varying complexities. [6][7][8][9][10][11][12][13][14][15] Among hexoses present in a furanose form, three nat- 33 or to galactofuranosyl entities. 29,34,35,23 Among these natural products, most of the Galf units are connected with their aglycon through b-D D- (1!6) or b-D D-(1!5) linkages (Table 1).…”

Simple and Efficient Method for the Synthesis of Galactofuranosides

“…An elegant extension of this method was demonstrated by McAuliffe and Hindsgaul (1997) by treatment of a peracetylated diethyl dithioacetal of D-galactose with acetyl chloride and boron trifluoride diethyl etherate to give the acyclic 1-chloro-(ethylthio) derivative 10. Glycosidation of acceptor 13 with donor 10 in the presence of AgOTf and Ag2CO3, provided S,O-acetal 14.…”