Mannopyranoside, methyl oxidation

Mannonic acid, 3-deoxy-D-, 75, 300 Mannopyranose, d-, oxidation of, 12 —, l,6-anhydro-/3-D-, 51 Mannopyranoside, methyl 3,6-anhydro-D-, 39... 

Additional evidence was provided by Hockett, Dienes and Ramsden,29 who compared the rates of oxidation with lead tetraacetate of styracitol and methyl a-D-mannopyranoside, and also of polygalitol and methyl... 

S. Signorella, M. I. Frascaroli, S. Garcia, M. Santoro, J. C. Gonzalez, C. Palopoli, V. Daier, N. Casado, and L. F. Sala, Kinetics and mechanism of the chromium(VI) oxidation of methyl-a-glucopyranoside and methyl-a-D-mannopyranoside,./. Chem. Soc. Dalton Trans. (2000) 1617-1623. 

Stoicheiometric RuOyCCl was also used to oxidise several furanoses, partially acylated glycosides and l,4 3,6-dianhydrohexitols [317] pyranosides to pyrano-siduloses [313] methyl 2,3,6-tri-O-benzoyl-a-D-glucopyranoside and its C-4 epimer to the a-D-xy/o-hexapyranosid-4-ulose (Table 2.3) [317], and methyl 2,3,6-trideoxy-a-D-e 7f/tro-hexapyranoside to the -a-D-,g/yceri9-hexa-pyranosid-4-ulose, an intermediate in the synthesis of forosamine [318], It was also used to oxidise benzyl 6-deoxy-2,3-0-isopropylidene-a-L-mannopyranoside to the a-L-/yxo-hexapyranosid-4-ulose [319] and for oxidation of isolated secondary alcohol functions, e.g. in the conversion of l,6-anhydro-2,3-0-isopropylidene-P-D-man-nopyranose to the-P-D-/yxo-hexa-pyranos-4-ulose mannopyranose (Fig. 2.16, Table 2.3 [20, 320, 324]). 

This sugar was first prepared by Irvine and Moodie48 by the methyla-tion of methyl a-D-mannopyranoside with methyl iodide and silver oxide in the presence of methanol as solvent. The crystalline methyl tetra-methyl-a-D-mannoside yielded, on acid hydrolysis, sirupy 2,3,4,6-tetra-methyl-D-mannose. Methylation has been carried out subsequently using dimethyl sulfate and sodium hydroxide49 60 and by the reaction of the potassium salt of methyl a-D-mannopyranoside with methyl iodide in liquid ammonia.61 The Haworth methylation procedure has also been... 

Further illustration of the inadequacy of hypobromite oxidation for the conversion of glycosides to uronides is the work of Jackson and Hudson.79 Only a twelve percent yield of the brucine salt of methyl a-D-mannuronoside was obtained because of oxidative cleavage of the carbon chain of methyl a-D-mannopyranoside. 

Ault, Haworth and Hirst47 first synthesized the methyl a-D-glycoside methyl ester of 2,3,4-tri-O-methyl-D-mannuronic acid by successive treatment of potassium (methyl a-D-mannopyranosid)uronate with dimethyl sulfate and sodium hydroxide, and then methyl iodide and silver oxide. Although no crystalline derivatives were isolated, there is little doubt about its structure, since the authors48 subsequently proved the presence of a pyranose ring in the starting material for the synthesis, methyl 2,3-O-isopropylidene-a-D-mannoside. The uronic acid has also been synthesized by Smith, Stacey and Wilson,28 who oxidized methyl... 

The ring structure of methyl pyranosides was found by Criegee to be stable to lead tetraacetate oxidation,43 for methyl a-D-glucopyranoside and methyl a-D-mannopyranoside consume about two moles of oxidant per mole without concomitant production of formaldehyde. It was possible, therefore, to distinguish between aldohexofuranosides and aldohexopyranosides by this method. 

Oxidation of lactal with perbenzoic acid and anhydrous methanol leads to methyl 4-(/3-D-galactopyranosyl)-a -D-mannopyranoside (LVII)48-6 ... 

When the oxidation is carried out in methanol instead of water, the corresponding methyl a-D-mannopyranoside is formed. 

Bergmann and Wolff S reported a small yield (1 g.) of menthol a-D-glucuronide by the oxidation of 12 g. of menthol a-n-glucoside in pyridine solution with sodium hypobromite. Better yields were obtained by Smolenski, who oxidized methyl a-n-glucopyranoside with bromine and sodium carbonate a 30% yield of the methyl n-glucuronide (as the brucine salt) was reported. Jackson and Hudson obtained a 12% yield of the brucine salt of methyl a-n-mannuronide by the barium hypobromite oxidation of methyl a-n-mannopyranoside. 

The first observation of the instability of carbohydrate orthoesters toward alkali came from Haworth, Hirst and Miller in connection with their experiments on the simultaneous deacetylation and methylation of L-rhamnose methyl 1,2-orthoacetate. These authors noticed that methylation by methyl iodide and silver oxide in the presence of solid sodium hydroxide resulted in the formation of crystalline methyl tri-methyl-/3-L-rhamnopyranoside. A similar result was obtained by Bott, Haworth and Hirst on the simultaneous deacetylation and methylation of triacetyl-D-mannose methyl 1,2-orthoacetate by the use of excessive quantities of dimethyl sulfate and alkali. The reaction produced a mixture of a. and /3 forms of methyl tetramethyl-D-mannopyranoside but the yield was only 40%. When the acetylated orthoester was submitted to methylation with silver oxide and methyl iodide in the presence of sodium hydroxide, the product was mainly trimethyl-rhamnose methyl 1,2-orthoacetate. This result indicates that for the alkaline hydrolysis of orthoesters, hydroxyl ions are necessary. Such ions are present in the dimethyl sulfate-alkali process, but are absent in the methyl iodide treatment except when the reaction mixture contains a little water either by accident or from the decomposition of the sugar molecule. Haworth, Hirst and Samuels examined the behavior of dimethyl-L-rhamnose methyl 1,2-orthoacetate in alkaline solution. When the substance was heated under various conditions with 0.1 A alkali at 70 there was no appreciable hydrolysis at the end of ninety minutes, whereas at 80 for... 

If the reaction takes place via an anion or in a S 2 fashion, high yields of the product alkyl-cyclopropanes have been obtained. Thus, reaction of methyl 4,6-( -benzyIidene-2,3-dideoxy-2,3-C-[(7 )-(chloromethyl)ethylidene]-a-D-mannopyranoside (1) with lithium aluminum hydride in refluxing tetrahydrofuran gave methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-C-isopropylidene-a-D-mannopyranoside (2) in 89% yield. Similarly, treatment of chloromethylcyclopropane 3 with lithium triethylborohydride, followed by oxidation with pyridinium chlorochromate,. gave ishwarone (4) in 75% yield. ... 

Jackson and Hudson obtained a dicarboxylic acid (104), isolated as its crystalline strontium salt, in a yield of 20% by oxidizing methyl a-n-mannopyranoside in an aqueous solution of barium hypobromite. This acid, which is normally obtained by oxidation of the dialdehyde obtained by periodate oxidation of the n-glucoside, is most probably another example of a product arising from the cleavage of a bond between adjacent keto groups. Heyns found that changing the pH, in the catalytic oxidation of benzyl S-n-arabinop3Tanoside, to pH 7.3 resulted in the formation of a dicarboxylic acid (105) (isolated as its crystalline barium salt) in 42% yield. He considered this to be a further oxidation product of the 4-keto compound normally formed. 

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