C.E. Rist

A facile route to trans cyclic carbonates of sugars

Abstract Five-membered, cyclic carbonates are formed when vicinal trans -hydroxyl groups in D -glucopyranosides are treated with ethyl chloroformate in the presence of triethylamine. With these reagents, methyl 4,6- O -benzylidene-α- D -glucopyranoside 2,3-carbonate ( 2 ), methyl 2,6-di- O -(methylsulfonyl)-α- D -glucopyranoside 3,4-carbonate ( 5 ), and methyl 4- O -(ethoxycarbonyl)-6- O -( p -tolylsulfonyl)-α- D -glucopyranoside 2,3-carbonate ( 8 ) were prepared. In contrast, when pyridine is the base present, only acyclic carbonates are formed.

Reaction of starch with carbohydrate trans-carbonates☆

Abstract Mono- and poly-saccharides possessing certain substituted, vicinal, trans-hydroxyl groups are readily substituted onto starch. Such substitution occurs when a trans-fused, cyclic carbonate derivative of the saccharide is added to starch in the presence of a basic catalyst. Excellent yields of products result on addition of methyl 4,6-O-benzylidene-α- d -glucopyranoside 2,3-carbonate (or 2,3-thionocarbonate), and methyl 2,6-di-O-(methylsulfonyl)-α- d -??? 3,4-carbonate to starch in the presence of triethylamine. ??? of degree of substitution (DS) 0.40 and dextran carbonate of Ds 0.31 ??? with starch under various conditions, in the presence of different catalysts, to give ??? corresponding polysaccharide copolymers.

2,3-thionocarbonate and 2,3-carbonate derivatives of D-glucopyranosides

Abstract A unique sugar derivative, methyl 4,6- O -benzylidene-α- D -glucopyranoside 2,3-thionocarbonate, which contains a trans -fused ring-structure, was prepared in good yield by rearrangement of bis(methyl 4,6- O -benzylidene-2- O -thiocarbonyl-α- D -glucopyranoside) disulfide. The thionocarbonate was converted into the novel methyl 4,6- O -benzylidene-α- D -glucopyranoside 2,3-carbonate in 93% yield by treatment with silver nitrate. By following the same reaction sequence, 2,3-thionocarbonate and 2,3-carbonate groups were introduced into 6- O -tritylamylose. The rearrangement of bis( O -thiocarbonyl) disulfide derivatives provides a new route for the synthesis of carbohydrate thionocarbonates and carbonates previously unavailable.

Ring-opening reactions of trans-carbonates and thionocarbonates

Abstract The reaction of methyl 4,6- O -benzylidene-α-D-glucopyranoside 2,3-carbonate ( 1 ) and the corresponding 2,3-thionocarbonate ( 2 ) with various nucleophines was investigated. Under proper conditions, 1 and 2 reacted with methanol, benzyl alcohol, α-toluenethiol, ammonia, piperidine, and glycine to give the corresponding 2- O -and 3- O -carbonyl and thiocarbonyl adducts, which were obtained in crystalline form. In each reaction product the 2-isomer was preponderant.

Ethylidene derivatives of D-erythrose I. 2,3-O-ethylidene-β-D-erythrofuranose

Abstract The principal product of the acidic rearrangement of 2,4- O -ethylidene- D -erythrose, and of the ethylidenation of D -erythrose in aqueous acid, is found to be 2,3- O -ethylidene- D -erythrose. The structure of this previously reported compound, which has been isolated in the crystalline β- D -furanose form, has been confirmed by unequivocal proof. The ethylidene ring of this D -erythrose acetal has a profound effect on the properties anticipated for a reducing sugar. Reactions of the aldehyde group are hindered, and hemiacetal formation gives only the β- D -furanose form; an α- D anomeric hydroxyl group would be sterically hindered. No mutarotation is observed, and acylation gives derivatives of the β- D anomer only.

Thio sugars by isomerization of carbohydrate thionocarbonates

Abstract Certain thionocarbonate derivatives of sugars isomerize to the corresponding monothiolcarbonates in the presence of potassium iodide. Structural requirements for isomerization are that the thionocarbonate must include a primary carbon atom of the sugar in a ring and that there be no unprotected hydroxyl groups in the derivative. The 3-O-acetyl (1) and the 3-O-p-tolylsulfonyl (2) derivatives of 1,2-O-isopropylidene-α- D -glucofuranose 5,6-thionocarbonate gave the corresponding monothiolcarbonates (3) and (4) in excellent yields. In contrast, the parent compound unprotected at C-3 gave no monothiolcarbonate. Methyl 2,3-di-O-methyl-α- D -glucopyranoside 4,6-thionocarbonate (5) afforded the 4,6-monothiolcarbonate (7). With each isomerized product, thiolation occurred at the C-6 position. When treated under similar conditions, two carbohydrate cyclic thionocarbonates involving only secondary carbon atoms, and two acyclic thionocarbonates of fully protected sugars, underwent negligible isomerization.

O-(alkyl- and aryl-oxythiocarbonyl) sugar derivatives☆

Abstract Bis(1,2:5,6-di- O -isopropylidene-3- O -thiocarbonyl-α- d -glucofuranose) disulfide ( 1 ) in pyridine undergoes a fragmentation reaction when treated with excess methyl, ethyl, propyl, or butyl alcohols, or phenol, to give the corresponding O -oxythiocarbonyl derivatives ( 2 – 6 ). A faster reaction and higher yield result when iodine is included in the pyridine solution. The oxythiocarbonyl compounds are stable when distilled (near 190°) under diminished pressure. Selective, acid hydrolysis of 3- O -(ethoxythiocarbonyl)-1,2:5,6-di- O -isopropylidene-α- d -glucofuranose ( 3 gave 3- O -(ethoxythiocarbonyl)-1,2- O -isopropylidene-α- d -glucofuranose ( 10 ), which rearranged, on standing in triethylamine, to 1,2- O -isopropylidene-α- d -glucofuranose 5,6-thionocarbonate ( 12 ). Oxidation of 3 with lead tetraacetate or silver nitrate gave the corresponding 3- O -ethoxycarbonyl derivative ( 8 ), whereas reduction of 3 with Raney nickel gave 3- O -(ethoxymethylene)-1,2:5,6-di- O -isopropylidene-α- d -glucofuranose ( 11 ).

Migration of thiolthiocarbonyl groups in selectively protected methyl α-d-glucopyranoside xanthates

Abstract A series of benzylxanthate esters of methyl α- d -glucopyranoside selectively methylated at various hydroxyl groups was synthesized. The esters were converted into the corresponding xanthate salts, and their behavior was investigated under alkaline conditions typical of xanthation media. Results reveal that migration of thiolthiocarbonyl groups from the 2- or 3-position to the 6-position proceeds via the hydroxyl group at C-4. Direct migration across the pyranose ring from the 2- or 3-position to the 6-position was negligible. The (benzylthio)thiocarbonyl position for each ester was identified by n.m.r. spectroscopy. Primary substitution caused the signals for the two protons at C-6 to be displaced downfield by about 1.0 p.p.m., and secondary substitution caused a 2.4-p.p.m. downfield shift of the signals for protons at C-2, C-3, and C-4.

Migration of thiolthiocarbonyl groups of methyl α-d-glucopyranoside xanthates☆

Abstract If similar reactant ratios are used, the xanthation of methyl α- d -glucopyranoside parallels the xanthation of starch. Degrees of substitution in the range of 0.3–0.4 were achieved, and changes in distribution from secondary to primary positions were observed. Synthesis of the individual, isomeric, xanthate salts of methyl α- d -glucopyranoside, and treatment of each with 18% sodium hydroxide, showed that the 2-, 3-, and 6-xanthate salts rearranged to mixtures in each of which the 6-isomer preponderated. Evidence is presented suggesting that the 2-isomer migrates intramolecularly to the 6-isomer by way of the 3-isomer. However, observation of the presence of minor proportions of polyxanthates in these mixtures suggests that intermolecular migration of thiolthiocarbonyl groups also occurs.

Oxirane ring-opening reactions of 3-O-(2,3-epoxypropyl)-1,2:5,6-DI-O-isopropylidene-α-d-glucofuranose

Abstract Reactions are reported of the oxirane ring of 3- O -(2,3-epoxypropyl)-1,2:5,6-di- O -isopropylidene-α- d -glucofuranose with water, primary and secondary alcohols, lithium aluminum hydride, ammonia, primary and secondary amines, and dipotassium hydrogen phosphate. In most reactions, the expected products were obtained in quantitative yields.