Hexoside

Methyl 2-deoxy-39496-tri-0-p-nitrobenzoyl-p-T>- yxo-hexoside. A solution of 370 mg. of 2-deoxy-3,4,6-tri-0-p-nitrobenzoyl- -D-Zyxo-hexosyl bromide (5) in 15 ml. of dry dichloromethane is added to a stirred suspension of 500 mg. of silver carbonate in 100 ml. of absolute methanol. The mixture is stirred for 20 hours and filtered the silver salts are washed several times with warm dichloromethane. The combined filtrate and washings are evaporated to dryness under diminished pressure, and the residue is recrystallized five times from ether-dichloromethane, giving 61% of pure product, having m.p. 173°-174°C. and [ ]D + 36° in chloroform. 

Methyl 2-deoxy-P-v- yxo-hexopyranoside. A suspension of 170 mg. of the nitrobenzoylated hexoside (obtained in the preceding preparation) in 50 ml. of 0.01M methanolic sodium methoxide is stirred for 4 hours at room temperature. The solvent is removed at 40°C. under diminished pressure, and the residue is suspended in 15 ml. of water. The suspension... 

Rearrangement of methyl 4,6-0-benzylidene-3-deoxy-3-phenylazo-aldohexopyranosides with alkali provides a new route to hexosid-3-uloses (18). 

The reactivity at the C-4 position of hexose and hexoside sulfonates has been demonstrated in the gluco and galacto series and could undoubtedly be extended to other sugars as well. In another example (25), methyl 2,3-di-0-benzoyl-4-0-p-tolysulfonyl-a-D-glucopyranoside (18a) was treated with potassium thiocyanate in N,N-dimethylformamide at 140°C. for 9 hours to give the C-4 epimeric thiocyanato derivative 19 in 34% yield. The corresponding 4-p-bromobenzenesulfonate (18b) however, afforded a 55% yield of 19 in only 2% hours of reaction time. 

In view of the unexpected effects of the C-2 and C-3 substituents on the reaction of C-4 sulfonates, it is worthwhile to point out the observations made with some 2,3-dideoxy derivatives. Treatment of ethyl 2,3-dideoxy-4,6-di-0-methylsulfonyl-D-ert/ hro-hexopyranoside (40) with sodium iodide and acetone at 115°C. caused the displacement of the C-6 mesylate group selectively to give 41. Catalytic hydrogenation then gave the corresponding ethyl 4-0-methylsulfonyl-2,3,6-trideoxy- -D-en/ /iro-hexoside in good overall yield (83%) (72). 

An attractive feature in this reaction is the possibility of direct substitution and formation of unblocked sugar derivatives containing one or more chlorodeoxy function in essentially two steps. Another facet is the formation of methyl 4,6-dichloro-4,6-dideoxy-hexosides from certain methyl glycosides in one step. Such compounds could be valuable intermediates in the synthesis of dideoxy and diamino sugars of biological importance. 

D-/yAc>-hexoside from D-galactal, a reaction which defines the stereospecificity of glycosyl transfer to the acceptor oxygen atom. 

Based on the fact that methyl 2,3-anhydro-a-D-mannopyranoside (II) is hydrolyzed17 by sodium methoxide to give, on subsequent methyla-tion, a mixture of two methyl trimethyl hexosides (methyl 3,4,6-trimethyl-a-D-altropyranoside and methyl 2,4,6-trimethyl-a-D-glucopyranoside) it was anticipated that the action of ammonia on II would follow essentially the same course. This was found to be the case, for with ammonia II yielded compounds which were converted to methyl 4,6-dimethyI-3-aeetamido-a-altropyranoside (III) and methyl 4,6-dimethyl-2-acetamido-a-D-glucopyranoside (IV) (10% yield). 

Rates of Enzymatic Hydrolysis of Hexosides and Pentosides with the Same Ring... 

Fischer was intrigued by the fact that emulsin caused hydrolysis of both / -glucosides and / -galactosides but had no effect on either the a- or / -xylo-sides (33). Since, at the time, Fischer expected glycosides to be furanosides, he suggested that both the enzymes required the presence of a free hydroxyl group at position 5 of a hexoside. 

Kannan and coworkers also used M hydrochloric acid at 100° for the hydrolysis of neutral glycolipids 6 h was found sufficient for hydrolysis of galactolipids, but 12 h was required for complete cleavage of the glucose-ceramide bond. The use of standard ceramide mono- and di-hexosides subjected to hydrolysis for 12 h gave monosaccharide recoveries of >94%... 

Methyl-3,6-di-0-benzoyl-2-deoxy-a-D- Methyl-3,6-di-0=-benzoyl-2-deoxy-a-D-t/ reo-hexosid-4-ulose S [317]... 

An interesting application of the reaction with sulfuryl chloride consisted in the synthesis of a fully chlorinated hexoside.27 Treatment of methyl 2-chloro-2-deoxy-/3-D-galactopyranoside with sulfuryl chloride and pyridine in chloroform, followed by heating of the product with an excess of pyridinium chloride, afforded a tetrachloride, presumably methyl 2,3,4,6-tetrachloro-2,3,4,6-tetradeoxy-/3-D-allopy-ranoside. 

On treatment with sodium ethoxide in ethanol, methyl 2,4,6-tri-O-methyl-a- (72) and -/3-D-ribo-hexosid-3-ulose yielded l-deoxy-2-methoxy-4,6-di-0-methyl-D-hex-l-en-3-ulose (73) and several isomeric ethyl 2,3,6-tri-0-methylhexosid-3-uloses (74) (see Scheme 10).133 On alkaline degradation of methyl 2,3-di-0-ethyl-6-0-pro-pyl-a-D-xy/o-hexosid-4-ulose (75) with sodium 1-butoxide in 1-butanol, one mole of ethanol was released per mole of 75, indicating that the substituent at C-2 was preferentially eliminated. On mild, acid hydrolysis of the product, methanol, ethanol, and some 1-propanol were formed, consistent with fission at C-l, C-3, and, to some extent, C-6 (see Scheme 10).134... 

A. G. Cottrell, E. Buncel, and J. K. N. Jones, Chlorosulphate as a leaving group The synthesis of a methyl tetrachloro-tetradeoxy-hexoside, Chem. Ind. (Lond.) p. 522 (1966). 

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