A-D-Galactopyranosides

This indirect method of selective benzoylation at C-4 is of special interest in the galacto series (47). Reaction of methyl 4,6-O-benzylidene-a-D-galactopyranoside 97 with NBS afforded the corresponding 6-bromo-4-benzoate (98) in over 90% yield. The axial hydroxyl group at C-4... 

Trichloro-4,6,6 -trideoxygalactosucrose or6-chloro-6-deoxy-p-D-fructofuranosyl 4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside ( galactosucrose is a trivial name for the 4-epimer of sucrose)... 

Abbreviations All, allyl MP, dimelhylaminopyridine or 2,4,6-trimelhylpyridine MOM, methoxy-methyl Piv, pivaloyl Tr, trityl other abbreviations are the same. Obtained accompanied with the 3,4-0-( methyl orthoacetyl)-a-D-galactoside the 0-deacetyl derivative was also reported. Inserted as a reference reaction. A mixture of two diastereoisomers. On hydrolysis (R = F), 3,6-dideoxy-3,6-difluoro-D-glu-copyranose is formed. Methanolysis gives methyl 3-deoxy-3-fluoro-a-D-galactopyranoside. 

Fig. 16.—Circular Dichroism of Methyl 2-Acetamido-2-deoxy-a-D-galactopyranoside...

Methyl 3,6-anhydro-a-D-galactopyranoside to Methyl 3,6-anhydro-a-D-glucopyranoside... 

C7H12C1204 Methyl 4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside MCDGAL 31 366... 

C7H13BrOs Methyl 6-bromo-6-deoxy-a-D-galactopyranoside MGALBH 31 366... 

B. Liu and R. Roy, Synthesis of clustered xenotransplantation antagonists using palladium-catalyzed cross-coupling of prop-2-ynyl a-D-galactopyranoside, J. Chem. Soc. Perkin Trans., 1 (2001) 773-779. 

Although there were early reports on the selective acylation72,73 and p-toluenesulfonylation73 of methyl a-D-glucopyranoside, and the p-toluenesulfonylation of methyl a-D-galactopyranoside,74 to yield... 

The results of a study of the di- and tri-molar methanesulfonylation of methyl a-D-galactopyranoside suggested, amongst the secondary hydroxyl groups, a reactivity order of HO-2 > HO-3 > HO-4, and, from the latter reaction, the 2,3,6-triester could be isolated in 30% yield a similar reaction of methyl a-D-mannopyranoside gave the... 

Reactivity at 0-3, in addition to that at 0-4 and 0-6, was observed with methyl )3-D-galactopyranoside, which, when treated with sulfuryl chloride, yielded methyl 3,4,6-trichloro-3,4,6-trideoxy-/J-D-allopyranoside 2-(chlorosulfate) in 56% yield.352 In contrast, under similar conditions, methyl a-D-galactopyranoside gave352 methyl 4,6-dichloro-4,6-dideoxy-a-D-glucopyranoside 2,3-di(chlorosulfate). Further examples of the dependence of the reactivity on the configuration of C-l are the conversion of methyl 4,6-0-benzylidene-/3-D-glucopyranoside into methyl 4,6-0-benzylidene-3-chloro-3-deoxy-/3-i>allopyranoside by sulfuryl chloride,352 and of methyl 4,6-0-benzylidene-a-D-glucopyranoside, under similar conditions, into the 2,3-di(chlorosulfate).355... 

Dichloro-4,6-dideoxy-a-D-galactopyranosyl 4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside was obtained in 72% yield by the reaction of a,a-trehalose with sulfuryl chloride.367... 

The reaction of sulfuryl chloride with carbohydrates to give chloro-deoxy derivatives has been reviewed briefly in this Series.98 The reaction of sulfuryl chloride with monosaccharides has been shown to afford products in which the secondary hydroxyl groups are replaced by chlorine with inversion of configuration.68-75 Jones and coworkers reported that the reaction of methyl a-D-glucopyranoside with sulfuryl chloride and pyridine in chloroform at room temperature proceeds by way of the 4,6-bis(chlorosulfate) by an Sn2 process, with chloride as the nucleophile, to give methyl 4,6-dichloro-4,6-dideoxy-a-D-galactopyranoside 2,3-bis(chlorosulfate).74... 

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