Methyl p-galactoside

In a further example Crout demonstrated a major difference in product distribution when the A-acetylgalactosaminidase from Aspergillus oryzae transfers GalNAc to methyl aGalNAc or to methyl pGalNAc. Transfer to methyl a-galactoside resulted in 81% yield of the 1-4 linked product and only 9% of the 1-6 isomer whereas transfer to methyl P-galactoside resulted in almost equal amounts of the two isomers, but at lower yields (20% of the 1-4 isomer and 23% of the 1-6 isomer) [27]. 

Although we show only the methyl p-D-galactoside as a product, some of the a epimer will also be formed because the carbocation intermediate can be attacked at either face by the methanol. 

Regioselective acylations can also be achieved by the stannylene procedure but, in general, selectivities are not as high as for alkylations. For example, treatment of methyl P-D-galactoside with dibutyltin oxide followed by reaction with benzoyl chloride results in the formation of a mixture of methyl 6-O-benzoyl-P-D-galactoside (53%) and methyl 3,6-O-di-benzoyl- P-D-galactoside (21 %).40... 

Thus, refluxing methyl P-D-glucoside two equivalents of tributyltin oxide, [(C4Hg)3Sn]20 and molecular sieves (3 A) in chloroform for 2-3 h followed by treatment with two equivalents of bromine at 0 °C furnishes methyl p-D-3-dehydro-3-ketoglucoside in more than 90% yield. Similarly, methyl p-D-xyloside gives the 3-oxo compound, whereas methyl a-D-glu-coside, a-D-galactoside, a-D-xyloside, and p-L-arabinoside yield 70-80% of the corresponding 4-keto derivatives [734],... 

Some fluorogenic substrates have become popular of late. These are methyl umbilllferyl galactoside for the enzyme P-galactosidase and methyl umbilllferyl phosphate for the enzyme alkaline phosphatase. 

Carbonyl compounds are quantitatively reduced regio- and stereo-selectively by NaBH4 at room temperature in aqueous solutions containing glycosidic amphiphiles such as methyl-p-D-galactoside, dodecanoyl-p-D-maltoside, L-arabinose and sucrose [63]. a,P-Unsaturated ketones give 1,2-reduction to corresponding allylic alcohols and cyclohexanones furnish the thermodynamically more stable alcohol. The observed stereodifferentiation can be attributed to hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates. 

A convenient method for the removal of nitrate groups from the anomeric position, e.g., those introduced by azidonitration of glycals, involving treatment with benzenethiol and ethyldiisopropylamine, has been developed. A study on denitration with hydioxylamine in pyridine established that, whereas trinitrocellulose reacts at the 2-position with high selectivity, the denitration of monomeric model compounds (tetranitrates of methyl a- and P-D-glucopyranoside, methyl a-D-mannopyranoside, methyl p-D-galactoside) takes place... 

Sialic acids continue to gain prominence, and the chemical synthesis of sialic acid dimers and related matters has been treated in a short Japanese review. a-D-Neuraminic acid 2->6-linked to methyl P-D-galactoside has been reported, ... 

The method employing triphenyl phosphite methiodide, as adapted to carbohydrates,130 has been used for the synthesis of protected 4-deoxy sugars. From methyl 2,3-di-0-methyl-6-0-p-tolylsulfonyl-a-D-glucoside and the corresponding D-galactoside, epimeric 4-iodo derivatives were obtained these were both reduced to methyl 4-deoxy-2,3-di-0-methyl-b-0-p-tolyl-sulfonyl-a-D-zj/Zo-hexoside. 

Hot absolute methanol containing p-toluenesulfonic acid effected226 de-acetonation of methyl 3,4-0-isopropylidene-2,6-di-0-tosyl-a-D-galactoside. 

For similar reasons, that is to investigate the inhibition of adhesion of pathogens to glycolipid receptors in host cells, Magnusson and co-workers [146] have prepared the 3-0-methyl-, 3-deoxy-3-C-methyl and the 3-deoxy derivatives of the P-methyl glycoside of the disaccharide gal-a-(l -> 4)-gql. The P-methyl galactoside (150) was converted into the benzyl ether (151) using benzyl trichloracetimidate [147] and then... 

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