The Mercaptolysis of Glucose and Galactose Pentaacetates

Lemieux, R. U.

doi:10.1139/v51-127

Cited by 95 publications

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References 17 publications

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“…Under the influence of the acid catalyst (A), the transition state 111 is achieved. I t is deemed necessary to postulate the participation of the C2-acetoxy group in the loosening of the C l to ~nethoxyl group bond in view of the strong activation this participation appears to provide to the reaction (7,8).…”

Section: Fig 3 Calc~~lated Curves (Using Eq~lations [S] [Gi 181 mentioning

confidence: 99%

“…Thus, it was clear that the acetolysis of methyl a-D-glucopyranoside tetraacetate proceeds mainly with inversion of the anomeric center to yield P-D-glucopyranose pentaacetate. I t is noteworthy in this respect that a-D-glucopyranose pentaacetate undergoes mercaptolysis (7) and acetolysis (9) with inversion of the anomeric centera stereochemical route which has long been recognized for the reaction of acetylated a-D-glucopyranosyl halides under conditions for the IcoenigsI<norr type of reaction (6,10,16).…”

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confidence: 99%

“…Equations [5] and [B] Thus, for scheme 1, the con~position of the reaction product after any given time could be calculated using equations [5], [GI, [7], and [8] and the same could be done for scheme 2 by employing equations [5], [B], [TI, and [9]. The results of these calculations are plotted in Fig.…”

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confidence: 99%

“…Therefore, the identification by Lindberg (13) of only about 8% heptaacetate in the product from the acetolysis of methyl a-D-glucopyranoside tetraacetate suggests that for this coinpound the preferred reaction route was direct acetolysis of the C1 to methoxyl group bond. The C1 to acetoxy group bold of b-D-glucopyranose pentaacetate has been shown to be highly susceptible to dissociation a s compared t o the corresponding bond in the a-anomer (7,8). I t would therefore be surprising indeed if conditions which readily cleave the C1 to methosyl group bond of methyl a-D-glucopyranoside tetraacetate would not dissociate much Inore reaclily the corresponding bond in the b-anomer as is suggested by Lindberg's arguments in support of his theory for the mechanism of the ailomerization of acetylated glycopyranosides.…”

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confidence: 99%

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THE ACETOLYSES OF THEALPHAANDBETAMETHYLD-GLUCOPYRANOSIDE TETRAACETATES

Lemieux¹,

Shyluk²,

Huber³

1955

Can. J. Chem.

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The acetolyses of the alpha and beta methyl D-glucopyranoside tetraacetates in 1 : 1 acetic acid -acetic anhydride 0.5 11d with respect to sulphuric acid were followed a t 25'C. by isotopic dilution analysis of products isolated after various intervals of tirne. The reaction of the a-glucoside was found to proceed mainly with inversion of the anomeric center. On the other hand, the 0-glucoside was found to undergo acetolysis with retention of configuration concurrent with anomerization. I t was shown t h a t the polarimetric changes observed in the course of the reactions could be satisfactorily accounted for on the basis of these reaction routes. Reaction mechanisms are suggested. Montgomery et al. (15) investigated the use of either sulphuric acid or zinc chloride in acetic acid -acetic anhydride as a reagent for the acetolysis of glycosides. I t was shown that in many cases the glycoside was converted to a mixture of the anomeric sugar acetates in high yield and the procedure has been widely used for the cleavage of acetal bonds in carbohydrate chemistry. Studies on the acetolysis of the anomeric methyl D-arabinopyranoside triacetates showecl these reactions to be highly complex (15). A solution a t 20°C.of nlethyl a-D-arabinopyranoside triacetate in a mixture of 4y0 sulphuric acid in 7 : 3 acetic anhydride -acetic acid changed sharply in specific rotation from -lgO to -114O in one minute and declined to an equilibrium value of -ZO a t the end of 20 min. The hexaacetate of aldel~ydo-D-arabinose and p-D-arabinopyranose tetraacetate were isolated in yields of soy0 and 12%, 1-espectively, from the product. However, when the experiment was interrupted a t the rotation peak of -114", a 14% yield of methyl /3-D-arabinopyi-anoside triacetate was obtained. Thus, it was apparent that the rapid initial rise in rotation was d~~e to the anomerization of the a-anoiner to the more stable /3-form. This possibility was strengthenecl by the observ a t' loll that ~nethyl @-D-arabinopyranosicle triacetate under the same conditions gave a solution which changed in specific rotation from -184' t o a constant equilibrium value of -17" in three minutes. The hcxaacetate and the p-tetraacetate could be isolated in 56y0 and 11% yields, respectively, after 24 hr. The occurrence of the hexaacetate in the reaction products suggested that the C1 to ring-oxygen bond may cleave in preference to the C1 to methoxyl group bond. This idea was substantiated by the acetolysis of the p-arabinoside under the milder conditions of O.l6Y0 sulphuric acid in 7 : 3 acetic anhydride -acetic acid mixture. Both the anomeric forms of methyl hemiacetal pentaacetates (I) were isolated in good and approximately equal yields. I t is to be notecl that liLl~nz~script received September 7 , 1954 More recently, Lindberg (1, 2, 13) has obtained further evidence that the acetolysis of an unstable 0-acetylated allcyl glycopyranoside is accompanied by anomerization. This was shown to be so for a variety of glucosides (13), galactosides ( I ) , and a xyloside (2...

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Section: Fig 3 Calc~~lated Curves (Using Eq~lations [S] [Gi 181 mentioning

confidence: 99%

mentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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THE ACETOLYSES OF THEALPHAANDBETAMETHYLD-GLUCOPYRANOSIDE TETRAACETATES

Lemieux¹,

Shyluk²,

Huber³

1955

Can. J. Chem.

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“…Furthermore, reaction by way of the ion (11) is highly attractive from energy considerations (7). The conformation of the ion (11) is based on the established conformation of six-membered rings fused 1,2-cis to planar five-membered ring (1, 4) and on the evidence provided by Lemieux and Brice (9) that the CHlOAc group must be situated in close proximity to the anomeric center.…”

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THE PREPARATION AND PROPERTIES OF α-D-GLUCOPYRANOSE 1,2-(ETHYL ORTHOACETATE) TRIACETATE

Lemieux¹,

Cipera²

1956

Can. J. Chem.

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Thioglycosides

Ernst

Hart

Sînaÿ

2000

Carbohydrates in Chemistry and Biology

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Thioglycosides are not very common in nature, only a few simple alkyl and aryl thioglycosides have been found as constituents of antibiotics from Streptomyces species [ 1-31. Although not really thioglycosides, glucosinolates with an anomeric sulfur are also well-known natural compounds [4, 51. In spite of their low natural abundance, thioglycosides and their chemistry have for a long time been a field of interest for many researchers, the first thioglycoside was synthesized in 1909 [6], and their basic chemistry was early reviewed [4, 71. But it is only recently that their excellent glycosyl donor qualities have been recognized. In the beginning of the seventies the first successful synthesis of a disaccharide was performed [S], but it was not until the middle of the eighties that enough efficient promoters were discovered to make glycosylation with thioglycoside donors into a general and accepted method. Since then and in a very short time-span, thioglycosides have become one of the most used type of donors, especially in glycosylations with oligosaccharide donors (block synthesis). There are already some reviews on the subject [9-121, and in the most recent complete list of published glycosylations during one year (1994) [ 131, thioglycosides were used as donors in about 20% of all reported glycosylations and in 35% of all couplings using oligosaccharide donors, competing well with the long established halide donors and the trichloroacetimidate method.The strength of thioglycosides as glycosyl donors is their easy synthesis (Section 4.2) combined with their stability, withstanding most reaction conditions used in e.g. protecting group manipulations and glycosylations, and at the same time their effective acth ation using chemoselective thiophilic promoters (Sections 4.3.2 and 4.4.1) and also easy transformation into other types of glycosyl donors (Section 4.3.1). Hence, they are perfectly fitted to be used in block synthesis of oligosaccharides, where stable oligosaccharide donors are a prerequisite. Their stability also makes them very apt in synthetic schemes where a number of chemical modifications are performed just prior to the glycosylations, as, e.g., in various types of Carbohydrates in Chemistry and Biology

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The Mercaptolysis of Glucose and Galactose Pentaacetates

Cited by 95 publications

References 17 publications

THE ACETOLYSES OF THEALPHAANDBETAMETHYLD-GLUCOPYRANOSIDE TETRAACETATES

THE ACETOLYSES OF THEALPHAANDBETAMETHYLD-GLUCOPYRANOSIDE TETRAACETATES

THE PREPARATION AND PROPERTIES OF α-D-GLUCOPYRANOSE 1,2-(ETHYL ORTHOACETATE) TRIACETATE

Thioglycosides

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