Galactopyranose carba

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. " ... 

When carba-a-DL-galactopyranose (6) reacts with a, a-dimethoxy-toluene, there are obtained two stereoisomers, 69 and 70, whose structures... 

Starting from (—)-29, carba-a-D-galactopyranose (7) and carba-) -D-glu-copyranose (94) have been synthesized by a reaction analogous to that employed in the preparation of the racemates. - ... 

Carba-a-D-galactopyranose (7) has also been synthesized from quebrachi-tol, by Paulsen and coworkers,as well as carba- -D-mannopyranose (114). 

The 4-0- (282) and 4,7-di-O-methanesulfonates (283) of a-DL-carba-galactopyranose obtained from 258 produced, after azidolysis in DMF, hydrogenolysis, and acetylation, penta-A, 0-acetyl-4-amino- (284) and 4,7-diamino-4,7-dideoxy-o -DL-carba-glucopyranose (285). 

As mentioned earlier, a-D-carba-galactopyranose (1) has been found in a fermentation broth of Streptomyces sp. MA-4145, as an antibiotic. The potency of the antibiotic was rather low. A concentration of—125 fig/mh is required in order to produce a standard inhibition zone of 25-mm diameter against Klebsiella pneumoniae MB-1264, using 13-mm assay discs in a disc-plate assay. A sample of the synthetic a-DL-carba-galactopyranose (17) was... 

Slight changes in protecting groups of the cyclization precursor (Scheme 8.22) allowed the syntheses of 5a-carba-a-D-glucopyranose and 5a-carba-a-D-galactopyranose. Thus, as shown in Scheme 8.23, compound 81 was obtained from D-mannose in a similar fashion as for derivative 77 and gave, under radical cyclization conditions, carbocychc compounds 82 and 83 in 74% yield as a... 

The syntheses of carba-P-o,L-fucopyranose and carba-P D,L-galactopyranose have been reported from 3-0-benzyl-l,2 4,5-di-0-cyclohexylidene-m> o-inositol. They involved the deoxygenation of the 6-OH, the conversion of the 1-OH into a ketone, and the addition of methylmagnesium bromide (for producing the fuco derivative) or benzyloxymethyllithium (for producing the galacto derivative) followed by deoxygenation and deprotection as the key step. ... 

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