D-Glucopyranose pentaacetate

The synthesis of a bridgehead sulfonium salt analogue 59, of the naturally occurring glycosidase inhibitor castanospermine, proceeded by a multistep procedure starting from 5-thio-d-glucopyranose pentaacetate <2000JA10769>. The desired bicyclic sulfonium salt 57 could not be obtained from the key bromide precursor... 

The first attempt to establish the mechanisms of the anomerizations was published by Bonner.79 An extensive study was made of the anomerizations of the D-glucopyranose pentaacetates in mixtures of acetic anhydride and acetic acid in the presence of sulfuric acid. The rate of reaction was found to be greatest in pure acetic anhydride. The anomerizations were shown to be inversions specific for the anomeric center. The data did not allow definite conclusions regarding the reaction mechanisms. Nevertheless, a mechanism was proposed, for both the forward and reverse reactions, which appeared the most attractive of those which could be postulated to account for the experimental facts that the anomerization... 

Assuming that the mechanism involves dissociation of the Cl-to-acetoxy-group bond, the Lewis acid, stannic chloride, undoubtedly would catalyze the anomerization of /3-D-glucopyranose pentaacetate by complexing with the Cl-acetoxy group, to lead to the equilibrium represented by equation 4, where G represents /3-D-glucopyranose. 

The D-mannopyranose pentaacetates were treated with stannic trichloride acetate (labeled with carbon14 in the carboxyl group) in chloroform solution, in the presence of stannic chloride. The rate at which radioactivity was introduced into the sugar acetate was followed. The exchange had been shown to be specific for the Cl-acetoxy group of the D-glucopyranose pentaacetates,33 and this was assumed in the present... 

The preparation of /3-acetochloro-D-glucose through the interaction of titanium tetrachloride with /3-D-glucopyranose pentaacetate in chloroform... 

D-glucopyranose pentaacetate (LXVII) to carbonium ions, followed by a rapid reaction of these ions with chloride ions derived from the catalyst. Since the ions were essentially in the 1,2-a-cyclic structure (LXYIII), the /S-l,2-frans-halide (LXXIX) was the main product of the initial reaction. On prolonging the reaction, rearrangement to the normal 1,2-cfs-aceto-chloro-D-glucose occurred. 

The velocity constant for the compound XCIXc was about 2.3 X 10 3 min.-1. The reaction of compound Cc was also very slow. The results therefore indicate that the introduction of chlorine atoms on the C2-acetoxy group has the same effect on the anomerization of glucoside as it has on the acetate. The fact that methyl glucosides react faster than the corresponding acetate appears opposite to all expectation. It must be remembered, however, that /J-D-glucopyranose pentaacetate is rapidly dissociated under these conditions. The velocity constant was found101 to be 0.46 min.-1. 

The mechanism proposed by Lemieux and Brice33 for the anomeriza-tion of the D-glucopyranose pentaacetates suggested that the above prep-... 

Fig. 2.—Relative Rates of Mercaptolysis of the Pentaacetates of D-Glucopyranose and D-Mannopyranose in Ethyl Mercaptan at 0° in the Presence of Zinc Chloride 105 1, /3-D-Glucopyranose Pentaacetate 2, S-D-Mannopyranose Pentaacetate 3, a-D-Mannopyranose Pentaacetate 4, a-D-Glucopyranose Pentaacetate.

Mercaptolysis of /3-D-glucopyranose pentaacetate in ethyl mercaptan at 0°, with zinc chloride as catalyst, gives ethyl tetra-O-acetyl-l-deoxy-1-thio-/S-D-glucopyranoside in 71% yield. Under the same conditions, a-D-glucopyranose pentaacetate reacted only very slowly, but it could be shown that the deoxy-thio-/3-D-glucoside is formed in much greater amount than is the a anomer. Mercaptolysis of the D-mannopyranose pentaacetates under the same conditions for 48 hours resulted in a 70% yield of ethyl tetra-O-acetyl-l-deoxy-l-thio-a-D-mannopyranoside from the /3-D-pentaacetate, and in a 60% yield from the a anomer.103 Inspection, by preparative paper chromatography, of the residual sirups, after deacetylation, led in each case to the isolation of the anomeric ethyl-1-... 

The kinetics of the acid-catalyzed anomerizations of D-glucopyranose pentaacetates in mixtures of acetic anhydride and acetic acid have been investigated by a number of workers. According to Painterthe equilibrium mixture contains approximately 87 % of the a anomer, in nearly... 

D-Glucitol (sorbitol) hexaacetate, n-inannitol hexaacetate 0-D-Glucopyranose pentaacetate a-D-Arabinopyranose tetraacetate... 

When a- or 8-D-glucopyranose pentaacetate is treated with piperidine (three molecular proportions are best), deacetylation occurs on Cl and C2, and the product is iV -(3,4,6-tri-0-acetyl-D-glucosyl)piperidine, whose structure was proved by conventional methods, including its conversion into 2-0-methyl-D-glucose. The same triacetate is obtained when piperidine reacts with 3,4,6-tri-O-acetyl-D-glucosyl chloride or with D-glucose 2,3,4,6-tetraacetate. Loss of the acetyl group on C2 must accompany or... 

AGLU a-form of 1,2,3,4,6-Pentaacetyl-D-glucose BGLU /f-form of 1,2,3,4,6-Pentaacetyl-D-glucose Synonyms o-Glucose pentaacetate D-Glucopyranose pentaacetate Source Raveendran, P Wallen, S. L. J. Am. Chem. Soc. (2002), 124(25), 7274-7275. 

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