Labile carbohydrates

The Tetrabenzylglycosyloxycarbonyl(BGloc)-Group -An Enzyme Labile Carbohydrate Derived Urethane Blocking Group, T. Kappes, H. Waldmann, Carbohydr. Res. 1998, 305, 341-349. 

Scheme 13.13 Synthesis of a type II collagen analog using acid-labile carbohydrate...

The detachment of the glycopeptide from the resin and deprotection of the amino acid side chains as well as the removal of the acid-labile carbohydrate protecting groups were simultaneously carried out using TFA/H20/thioanisole/ethanedithiol (87.5 5 5 2.5). This treatment proceeded without affecting the glycosidic bonds and furnished the target molecule 38. 

Degradation of labile carbohydrates High temperature Work at room temperature... 

FIGURE 103 Identification of a glycopeptide produced by peptic digestion of a monoclonal antibody using accurate mass measurements (the peptide mass matches two possible iso-baric fragments from the protein sequence, and application of CAD fails to provide useful sequence information due to the presence of a labile carbohydrate chain). The identity of this peptide is unequivocally established using accurate mass measurements with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS).TOFMS,time-of-flight mass spectrometry. 

The carbohydrate moieties of erythrocytes from patients with Tn-syndrome have been shown to contain less o-galactose and sialic acid. - The work suggested that alkali-labile carbohydrate chains of these erythrocytes consist solely of 2-acetamido-2-deoxy-D-galactosyl residues linked either to serine or to threonine. 

Although extremes of pH or pD (outside the range 6 5-8) are to be avoided, buffer solutions are only necessary in two cases if the molecule is charged, and the charge state is relevant to the study and in the study of acid-labile carbohydrates, such as sia-lylated oligosaccharides. 

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. 

FI and FD are mild or soft methods of ionization that produce abundant molecular or quasi-molecular positive or negative ions from a very wide range of substances. In the FD mode, it is particularly useful for high-molecular-mass and/or thermally labile substances such as polymers, peptides, and carbohydrates. 

As a rule of thumb, one can say that the efficiency of separation of mixtures and the simplicity of operating and maintaining apparatus are much greater for GC than for LC. Hence, other things being equal, GC is most often the technique of first choice and can be used with a very wide variety of compound types. However, for nonvolatile or thermally labile substances like peptides, proteins, nucleotides, sugars, carbohydrates, and many organometallics, GC may be ruled out completely... 

FAB has been used with a wide variety of substances, including thermally labile compounds such as peptides, sugars, carbohydrates, and organometallics. 

IonPac KC-811 column separated the labile compounds N-acetylneuraminic acid and N-glycolylneuraminic acid released by mild acid hydrolysis of bovine vitronectin.245 Sialic acid is extremely labile to conditions of handling and must be released by mild acid hydrolysis.246 Derivatization with phe-nylisothiocyanate and separation by reversed phase chromatography was found useful in analysis of hexosamines from gastric mucosa.247 A review on separation of sugars and other carbohydrates which covers many important aspects is available.248... 

The sucrose content of oral liquids may cause significant problems when these products are prescribed for long-term therapy (e.g., asthma, seizure control, recurrent infections). Oral liquid preparations can represent a substantial carbohydrate load to children with labile diabetes, particularly if a child is ingesting more than one liquid medication with a high sugar content. 

The isomerism existing between the pairs of nucleotides was attributed to the different locations of the phosphoryl residues in the carbohydrate part of the parent nucleoside,49 63 since, for instance, the isomeric adenylic acids are both hydrolyzed by acids to adenine, and by alkalis or kidney phosphatase to adenosine. Neither is identical with adenosine 5-phosphate since they are not deaminated by adenylic-acid deaminase,68 60 and are both more labile to acids than is muscle adenylic acid. An alternative explanation of the isomerism was put forward by Doherty.61 He was able, by a process of transglycosidation, to convert adenylic acids a" and 6 to benzyl D-riboside phosphates which were then hydrogenated to optically inactive ribitol phosphates. He concluded from this that both isomers are 3-phosphates and that the isomerism is due to different configurations at the anomeric position. This evidence is, however, open to the same criticism detailed above in connection with the work of Levene and coworkers. Further work has amply justified the original conclusion regarding the nature of the isomerism, since it has been found that, in all four cases, a and 6 isomers give rise to the same nucleoside on enzymic hydrolysis.62 62 63 It was therefore evident that the isomeric nucleotides are 2- and 3-phosphates, since they are demonstrably different from the known 5-phosphates. The decision as to which of the pair is the 2- and which the 3-phosphate proved to be a difficult one. The problem is complicated by the fact that the a and b" nucleotides are readily interconvertible.64,64... 

In bipolar depression, patients often have mood lability, hypersomnia, low energy, psychomotor retardation, cognitive impairments, anhedo-nia, decreased sexual activity, slowed speech, carbohydrate craving, and weight gain. 

The observation of a stereoconvergent cyclization by Roy et al. [18], as shown in the third example, is of special interest from a synthetic point of view because it exploits the configurational lability of radicals in a favorable manner. The other examples, i. e. Nugent and RajanBabu s cyclization of a carbohydrate-derived epoxide [5d] and Clive s quinane synthesis [19], amply demonstrate the usefulness of the titanocene-initiated epoxide opening. 

Acid-labile linkages of carbohydrates are commonly those of furano-sidic sugar residues or of deoxy monosaccharides.50,63 Consequently, neuraminic acid and fucose residues, which occur as terminal monosaccharides of protein- and lipid-linked glycans, are removed by hydrolysis with a dilute acid. The linkages formed by these two sugar residues can conveniently be differentiated by subjecting a portion of... 

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