Carbohydrates methylation

The reagent is used to cleave carbohydrate methyl ethers. A suspension of the methyl ether in methylene chloride is cooled to —70°, boron trichloride is distilled in, and the mixture is kept at —70° for I hr. with occasional stirring. 

Needs, P. W., Selvendran, R. R. (1993). Avoiding oxidative degradation during sodium hydroxide/methyl iodide-mediated carbohydrate methylation in dimethyl sulfoxide. Carbohydrate Research, 245, 1-10. 

Phase transfer catalysis has been used in the methylenation of carbohydrates methyl 4,6-0-benzylidene-glucosides and galactosides gave the /raw -fused 2,3-acetals in about 60% yield with methylene dibromide and alkali. Methyl jS-D-ribofuranoside gave the fully substituted dimeric compound (1), and its 5-trityl derivative afforded the monomeric 2,3-acetal as anticipated, ... 

C has been used on carbohydrates. Methyl 6 - and /S-D-gluco-pyranoside, which are poorly soluble in the reaction mixture, gave 4,0% yields of the 6-0-acetate, while more soluble substrates underwent further acetylation at secondary hydroxy groups. The stereo-isomeric composition of products of acetolysis and acetylation of... 

The most stable protected alcohol derivatives are the methyl ethers. These are often employed in carbohydrate chemistry and can be made with dimethyl sulfate in the presence of aqueous sodium or barium hydroxides in DMF or DMSO. Simple ethers may be cleaved by treatment with BCI3 or BBr, but generally methyl ethers are too stable to be used for routine protection of alcohols. They are more useful as volatile derivatives in gas-chromatographic and mass-spectrometric analyses. So the most labile (trimethylsilyl ether) and the most stable (methyl ether) alcohol derivatives are useful in analysis, but in synthesis they can be used only in exceptional cases. In synthesis, easily accessible intermediates of medium stability are most helpful. 

Aspartame is the market leader among artifi cial sweeteners It is a methyl ester of a dipeptide un related to any carbohydrate It was discovered in the course of research directed toward developing drugs to relieve indigestion... 

Ethers are formed under conditions of the Williamson ether synthesis Methyl ethers of carbohydrates are efficiently prepared by alkylation with methyl iodide m the presence of silver oxide... 

Etherification. Carbohydrates are involved in ether formation, both intramoleculady and intermoleculady (1,13). The cycHc ether, 1,4-sorbitan, an 1,4-anhydroalditol, has already been mentioned. 3,6-Anhydro-a-D-galactopyranosyl units are principal monomer units of the carrageenans. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers of cellulose (qv) are all commercial materials. The principal starch ethers are the hydroxyethyl and hydroxypropylethers (see Cellulose ethers Starch). 

Methyl metacrylates, alcohols, aromatic and aliphatic carbohydrates, acetic ester acids are detected using he vapour-phase method. 

Candida cylindracea, phosphate buffer pH 7, Bu20. The 6-0-acetyl of Q -methyl peracetylglucose was selectively removed. Porcine pancreatic lipase will also hydrolyze acetyl groups from carbohydrates. These lipases are not specific for acetate since they hydrolyze other esters as well. In general selectivity is dependent on the ester and the substrate. ... 

Cellobiose was prepared first by Skraup and Konig by the saponification of the octaacetate with alcoholic potassium hydroxide, and the method was improved by Pringsheim and Merkatz.3 Aqueous barium hydroxide also has been employed for the purpose, and methyl alcoholic ammonia has been used extensively for the hydrolysis of carbohydrate acetates. The method of catalytic hydrolysis with a small quantity of sodium methylate was introduced by Zemplen,i who considered the action to be due to the addition of the reagent to the ester-carbonyl groups of the sugar acetate and the decomposition of the addition compound by reaction with alcohol. The present procedure, reported by Zemplen, Gerecs, and Hadacsy, is a considerable improvement over the original method (see Note 2). 

Vasella has used deoxy-nitro sugars for the synthesis of various biologically important carbohydrates, and the radical nitromethyladon of deoxy-nitro sugars has been used for synthesis of fnictose 6-phosphate" and 6-C-methyl and 6-C-rhydroxymethyl analogiies of iV-acetylnenraitinic acid fsee Scheme7.2. ... 

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