Glucopyranosyl bromide salts

Cinnolin-3(2//)-one (7) is methylated with diazomethane or methyl sulfate to give 2-methylcinnolin-3(2H)-one. In a similar manner, benzylation with benzyl chloride, cyanoethylation with acrylonitrile in the presence of benzyltrimethylammonium hydroxide and glucosidation with tetra-O-acetyl-a-o-glucopyranosyl bromide in the presence of a base affords the corresponding 2-substituted cinnolin-3(2//)-ones. However, glucosidation of the silver salt of cinnolin-3(2//)-one produces the corresponding O-substituted compound. 

Thus, when the silver salt of 2-quinoxalinone is condensed with tetra-O-acetyl-cr-D-glucopyranosyl bromide in xylene, the 2-glucosyl-quinoxaline (233 R = H R = Ac) is isolated. The latter compound is readily deacetylated to the glucoside (233 R = R = H). During the reaction only the 2-O-substituted derivative is formed (steric factors probably inhibit /V-glucosidation), and only the / -D-anomers are obtained.234... 

For instance, starting with a 2,3-di-O-isopropylidene-a-D-mannopyranoside 52, an attack by dibromomethyl-methyl ether (DBE) yields the 2,6-dideoxy-2-bromo-3-0-formyl-a-D-glucopyranosyl bromide 53. In the presence of a silver salt, predominantly P-glycosides like 54 are formed [21-23], Little is known about the mechanistic aspects, however, the stereoselectivity favors a 1,2-bromonium ion intermediate. 

One of the first syntheses of nucleosides was reported by Fischer and Helferich and involved condensation of the silver salts of both 2,6,8-trichloropurine and 2,8-dichloroadenine with 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide to form glycosyl derivatives.These nucleosides were fully characterized much later. 

The triethylammonium salt of a cyclic tellurolophosphate was similarly prepared. The salt was not isolated but reacted with a glucopyranosyl bromide. ... 

Although Koenigs and Knorr isolated a small yield of methyl /3-n-gluco-pyranoside (as such) from a solution of tetra-O-acetyl-a-D-glucopyranosyl bromide in methanol that had stood at room temperature for several days, it is customary to add an acid acceptor to speed up the reaction and to prevent deacetylation of the product. Silver, in the form of the oxide or a salt, was the first acid acceptor to be employed, and is still the one in most common use. Unless the aglycon is a simple alcohol, it is usual to dissolve the reactants in a solvent, which is often an organic base to act as an additional acid acceptor. Walden inversion at Cl is almost the invariable rule when the reaction is done in the presence of silver ion. Under special circumstances, however, both anomeric glycoside acetates may be obtained. ... 

Helferich and Wedemeyer - found that a wide miscellany of metallic oxides and salts and other compounds, including albumin, are efficient acid acceptors in the condensation of tetra-O-acetyl-a-D-glucopyranosyl bromide with methanol at room temperature to give methyl tetra-O-acetyl-/3-D-glucopyranoside. 

A solution of 6.6 g. of tetra-O-benzoyl-a-D-glucopyranosyl bromide, 1.6 g. of f-men-thol (dried over phosphorus pentoxide), and 2.5 g. of mercuric cyanide in 20 ml. of dry nitromethane was refluxed for 7 hr. with exclusion of moisture. The sirup obtained on evaporation under diminished pressure was dissolved in 20 ml. of hot benzene. On cooling, the mercury salts separated and were Altered. The residue after evaporation was crystallized from methanol (100 ml.) 5.6 g. (75% of the theoretical) twice recrystallized from ethanol m. p. 139-140°. 

These generalizations are illustrated by the recent synthesis of L-ascorbic acid glucosides 11 and 12 (16), The monosodium salt of ascorbic acid in N,N-dimethylformamide (DMF) affords exclusively the 03 monoalkylated derivative 9 on alkylation with 2,3,4,6-tetra-O-a-n-glucopyranosyl bromide. To obtain the 02 glucosylated derivative 10, under the same conditions, required the protection of the C3 hydroxyl as a methyl ether. Several workers have reported the biosynthesis of ascorbic acid glucosides in bacteria (17) however, the structure and position of glucosylation in these compounds has not been unambiguously determined. 

Tetra-O-acetyl-a-D-glucopyranosyl bromide (1) usually reacts with inversion at C, but it reacts with silver diphenylphosphate with retention of configuration. The phosphate ester (4) was isolated as the crystalline potassium salt. 

Reactions37" of Tigogenin (12) with Tetra-O-acetyl-a-D-glucopyranosyl Bromide (2) in Ether in the Presence of Silver Salts at 20°... 

Most mechanistic thinking in the area of glycoside synthesis is shaped by a seminal paper by Lemieux et al, in which an array of solvent-separated and intimate ion pairs is invoked, in heroic defiance of Occam s razor . The key discovery was that, whereas tetraacetyl a-D-glucopyranosyl bromide in a mixture of phenol and pyridine gave the p-pyridinium salt exclusively, in anhydrous pyridine anomeric mixtures were produced, and addition of tetra-ethylammonium bromide gave exclusively the a-anomer (Figure 3.38). Similar... 

To explore the dependence of the equilibrium on the nature of the anion, the fluoroborate salt of 59 was prepared. It was obtained at low temperature (0 ) either by the reaction of tetra-0-acetyl-/3-D-glu-copyranosyl fluoride (53) with boron trifluoride in carbon tetrachloride, or by treatment of tetra-O-acetyl-a-D-glucopyranosyl bromide (54) with silver fluoroborate in nitromethane. In edier, compound 54 and silver fluoroborate give a mixture of tetra-O-acetyl-a- and /3-D-glucopyranosyl fluoride, because the ether complexes with the boron trifluoride, and so a fluoroborate anion is no longer available. On dissolution of the fluoroborate salt of the D-gluco acetoxonium ion (59) in nitromethane or acetonitrile, an acyloxonium-ion rearrangement, is observed with consequent equilibration, between 59 60 61 62, that is not significantly different from... 

Kronzer FJ, Schuerch C. Methanolysis of some derivatives of 2,3,4-tri-O-ben-zyl-a-D-glucopyranosyl bromide in the presence and absence of silver salts. Carbohydr Res 1973 27 379-390. 

Sodium salts of 2-pyridone and cf a number of 3- and 5-substituted 2-pyridones and 3,S-disubstituted-2-pyridones when treated with tetra-O-acetyl-a-D-glucopyranosyl bromide in acetone give both the O- and yV-j3-gluco-sides. ... 

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