Galactopyranose group

Epimerization of 4 at C-2 provided 5a-carba-a-DL-galactopyranose (6). When the pentaacetate IS was heated in acetic acid containing sulfuric acid, epimerization occurred at C-2 through an intermediary cyclic acetoxonium ion (18), with anchimeric assistance of the vicinal, axial acetoxyl group. After acetylation, 5a-carba-a-DL-galactopyranose pentaacetate (19) was obtained in a yield of 14% it was converted into 6 by hydrolysis. The antimicrobial activity of the racemate 6 was found to be about half that of the natural antibiotic 7 in the same assay system, indicating that the L-antipode is probably inactive. " ... 

An alternative approach, in which the anomeric centre of the sugar is reacted with a carbon nucleophile, but the amino group is subsequently inserted at the other side or in both sides at the same time, is reported in Fig. 41 for the synthesis of a- and (3-homogalactonojirimycin.72 Reaction of 2,3,4,6-tetra-O-benzyl-p-D-galactopyranose with methylenetriphenylphosphorane generated an enitol on which the amino group was inserted as phtalimide by a double inversion process of the 5-OH, under Mitsunobu s conditions. 

Xanthates, on the other hand, are photolyzed to yield the corresponding alcohols, and the yield reported, for instance for l,2 3,4-di-0-iso-propylidene-6-0-[(methylthio)thiocarbamoyl]-a-D-galactopyranose (50%, see Scheme 13) is apparently lowered by partial removal of isopropyli-dene groups under the reaction conditions. 

In a preparation213 of 2,3,4-tri-O-benzyl-D-galactopyranose, allyl protecting-groups were removed from 0-1 and 0-6 of allyl 6-O-allyl-2,3,4-tri-0-benzyl- -D-galactopyranoside, and the allyl group has been used214 for the temporary protection of 0-2, 0-3, 0-4, or 0-6 in benzyl... 

Similarly, various a-D-glucopyranose derivatives having a mesyloxy group at C-4 and an acetoxyl group at C-l are also converted into 1,4-anhydro-/3-D-galactopyranose derivatives on treatment with sodium azide in such aprotic solvents as N,N-dimethylformamide.51 The use of sodium azide in N,N-dimethylformam ide under forcing conditions originated in attempts at nucleophilic displacements to form azido,... 

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