A-D-Altropyranoside, methyl

Several other methods for the introduction of halo atoms at C-6 in hexose derivatives have been known since the late 1920s. One of the earlier methods involved the reaction of methyl 2,3,4-tri-0-acetyl-6-0-trityl-a-D-glucopyranoside with phosphorus pentachloride which resulted only in an 8% overall yield of methyl 6-chloro-6-deoxy-a-D-glucoside (57). In contrast, the reaction of methyl 2,3,4-tri-0-acetyl-6-0-trityl-a-D-altropyranoside with phosphorus tribromide and bromine afforded a 73% yield of the corresponding 6-bromo-6-deoxy derivative (91). 

Methyl 2,6-anhydro-a-D-altropyranoside-2 5B g l,4-Anhydro-ot-D-allopyranose-Bi,4 9 1,2-0-Ethylidene-a-D-glucopyranose- S3 10 p-L-Altropyranose-2So... 

C21H20BrNO7S Methyl 4,6-0-benzylidene-2-0-(p-bromophenylsulfonyl)-3-cyano-3-deoxy-a-D-altropyranoside BZSALT 30 455... 

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). 

Methyl 4,6-O-benzylidene-a-D-altropyranoside showed little selectivity on reaction with a unimolar proportion of benzoyl chloride43 2-and 3-O-benzoyl and 2,3-di-O-benzoyl derivatives, together with starting material, were isolated in the molar ratios of 1 1.1 1.8 1. In contrast, benzoic anhydride in pyridine gave the 2-ester in 35% yield, with only a trace of the 3-benzoate. 

This class of acylating agents has thus far been but little used in carbohydrate chemistry. However, unimolar benzoylation of methyl 4,6-O-benzylidene-a-D-glucopyranoside, methyl 4,6-O-benzylidene-a-D-altropyranoside, and benzyl 4,6-O-benzylidene-jS-D-galactopy-ranoside with benzoyl cyanide gave good yields of the corre-... 

Many other glycosides have been subjected to selective chlorination with sulfuryl chloride. Methyl /3-L-arabinopyranoside afforded methyl 4-chloro-4-deoxy-a-D-xylopyranoside 2,3-di(chlorosulfate) in 29% yield, whereas the a-L anomer gave357 methyl 3,4-dichloro-3,4-dideoxy-/3-i)-ribopyranoside 2-(chlorosulfate) (30%). Methyl /3-d-ribopyranoside was converted into methyl 3,4-dichloro-3,4-dideoxy-a-L-arabinopyranoside through the action of pyridine hydrochloride on its 2,3,4-tri(chlorosulfate).358 Methyl a-D-lyxopyranoside gave only the 2,3,4-tri(chlorosulfate),353 as would be expected from the disposition of its hydroxyl groups, similar to that in the rhamno- and manno-pyranosides. Methyl a-D-altropyranoside was transformed into the 6-chloro-6-deoxy 2,3,4-tri(chlorosulfate) derivative in 80% yield.353... 

The reaction of methyl 2-azido-4,6-0-benzylidene-2-deoxy-a-D-altropyranoside (46) with 39 in refluxing 1,1,2,2-tetrachloroethane afforded a product which was formulated83(b) as methyl 2-azido-3,4-0-benzylidene-6-chloro-2,6-dideoxy-a-D-altropyranoside (47) the n.m.r. spectrum indicated that the product was a mixture of two diastereoisomers which differed in the configuration of the carbon atom of the benzylidene acetal. A possible mechanism for the formation of 47 is outlined. 

The reaction of 39 with methyl 4,6-0-benzylidene-2-deoxy-2-iodo-a-D-altropyranoside (48) gave a complex mixture of products, from which methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-eryf/iro-hex-2-eno-pyranoside (50) could be isolated. The formation of 50 was ex-plained83(b) by attack by chloride ion on the iodine atom in intermediate 49, followed by elimination of the substituent at C-3. Compound 50 itself reacts with reagent 39, and, therefore, prolonged reaction times led to extensive decomposition. 

A novel method of opening of oxiranes involves the use of (chlo-romethylene)dimethyliminium chloride (39) [see Section II,2c p. 250], monochlorodeoxy or dichlorodideoxy derivatives are obtained, depending upon the reaction conditions employed.83 Thus, methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside (110) reacts with 39 in 1,1,2,2-tetrachloroethane at room temperature to give, upon hydrolysis of the primary adduct 111 with an aqueous solution of sodium hydrogen carbonate, methyl 4,6-0-benzylidene-2-chloro-2-deoxy-3-0-formyl-a-D-altropyranoside (112). If a solution of 39 and 110 in 1,1,2,2-tetrachloroethane is heated at reflux temperature, methyl 3,4-0-benzylidene-2,6-dichloro-2,6-dideoxy-o -D-altropyrano-side (113) is obtained in high yield the n.m.r. spectrum of 113, like that of 47 (see Section II, 2c p. 250), showed the presence of two diastereoisomers which differed in the configuration of the benzyl-idene-acetal carbon atom. 

As might be expected, the nitrous acid deamination of methyl 2-amino-4,6-0-benzylidene-2-deoxy-a-D-altropyranoside (10) hydrochloride leads45,46 uniquely to methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside (11). The benzylidene group does not play an... 

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