Glycosides methanol

Methyl glycosides of 2 deoxy sugars have been prepared by the acid catalyzed addition of methanol to unsaturated sugars known as glycals... 

The use of penodic acid oxidation m structure determination can be illustrated by a case m which a previously unknown methyl glycoside was obtained by the reaction of D arabmose with methanol and hydrogen chlonde The size of the nng was identified as five membered because only one mole of penodic acid was consumed per mole of glycoside and no formic acid was produced Were fhe nng six membered fwo moles of penodic acid would be required per mole of glycoside and one mole of formic acid would be produced... 

The mechanism for formation of the 3 methyl glycoside is shown The mechanism for for mation of the a isomer is the same except that methanol approaches the carbocation from the axial direction... 

Crocin is a yellow-orange glycoside that is freely soluble in hot water, slightly soluble in absolute alcohol, glycerol, and propylene glycol, and insoluble in vegetable oils. Crocin melts with decomposition at about 186°C and has absorption maxima in methanol at about 464 nm and 434 nm. 

It was found that the reaction of the lactone glycosides (5/ )- and (5S)-5-methoxy-5-(2,3,5-tris-(9-benzoyl-/3-D-ribofuranosyl)-2(5//)-furanone270and271 with hydrazine hydrate in methanol gave two products the pyridazinone 272 and a mixture of diastereomeric A -aminopyrrolinones 273, which could not be separated, in yields of 26 and 71%, respectively (Scheme 70) (87JOC4521). 

The solubility of iridoids depends on their state (free, glycosylated, acetylated), but usually they are extracted with polar solvents methanol, ethanol, aqueous alcohols, and rarely acetone. Iridoid glycosides are more or less stable some of them are very sensitive to acids and alkalis. Some iridoid glycosides such as aucubin suffer color modification after chemical or enzymatic hydrolysis they give first a blue to green... 

Many solvents such as methanol, acetone, ethanol, and water are used for anthocyanin extraction due to their polar character since most anthocyanins occur naturally as glycosides. Anthocyanin glycosides have higher solubility in water than the corresponding aglycons. In addition, in most fruits and vegetables, anthocyanin pigments are located in cells near the surface. " ... 

Glycosides can be hydrolyzed by taking the extract to dryness and treating the dry residues with 7.5% hydrochloric acid under reflux for 30 min. The freed aglycones can then be recovered by serial extraction with portions of diethyl ether. The extracted aglycones are then redissolved in a small volume of a suitable solvent, usually acetone or methanol. 

Glycosidic anthraquinones may be developed using ethyl acetate-methanol-water systems (100 10 10) with suitable adjustments made for polarity. Similarly, aglycones can be separated using a somewhat less polar solvent such as petroleum ether (40 to 60°C)-ethyl acetate-formic acid (75 25 1). Some chosen retention data may be found in a recent monograph [24]. Pigments may be recovered by extraction of the absorbant with acetone or methanol after removal of the individual zones. 

Furthermore, there is no proof for over-oxidation of the primary alcohol of 5 in a carboxylate or for cleavage of the glycosidic bond and release of methanol under the conditions applied. However, additional signals in the NMR spectrum of the reaction mixture are observed between 80 and 85 ppm, which are ascribed to side products formed from 6 by aldol condensations in alkaline solution. 

For the extraction of colourants from Rubia tinctorum (Figure 13.2) roots, mostly methanol, [42] water-methanol (with the addition of n-amyl alcohol in the case of lake extraction)[19,20] or water-ethanol solutions[38] are used. Additional hydrolysis can be performed with hydrochloric acid[8,19,20,34] and trifluoroacetic acid,[42] but also with madder root enzymes,[42] responsible for cleavage of anthraquinone glycosides into the corresponding aglycones and sugars. 

Mild extraction was also found to be effective in the analysis of extracts of Flaveria haumanii, l in which quercetin, kaempferol, isorhamnetin as well as their glycosides and sulfate esters were identified. The obtained results were useful in the identification of the colourants from fibres from pre-Columbian Andean textiles extracted with the use of water-methanol solution with formic or hydrochloric acid. The components of each extract were separated on a reversed phase HPLC column and the eluates were monitored at... 

In about 1936, sialic acid was discovered by Blix, who found it to be a component of submaxillary-gland proteins, and who described many of its properties. However, little notice was taken of this work at the time it was published. In 1941, Klenk, who was working on glycolipids of the brain, described a compound, later shown to be a methyl glycoside of sialic acid, that had been obtained by treatment of a lipid fraction with 5% methanolic hydrogen chloride at 105°. In 1954, Klenk and Faillard reported the first isolation of pure N-acetyl-neuraminic acid from animal sources. 

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