Partially methylated alditol acetates separation

Oligosaccharides were isolated from PMII by weak acid hydrolysis and separation by SEC and HPAEC-PAD. The isolated oligosaccharides were desalted, reduced and methylated. GC-MS analysis of the partially methylated alditol acetates has been used to reveal the structure of the oligosaccharides. 

Multiple-ion monitoring is, however, of considerable value in structural studies, but only if model compounds of known structure are available for comparison. Such an approach has been used in the study of the carbohydrate structures of glycoproteins from different tissues.50 Separation of glycopeptides obtained from various tissues was performed on columns of concanavalin A-Sepharose. Structural analysis by multiple-ion monitoring of partially methylated, alditol acetates derived from the various fractions indicated that the glycopeptides were separated according to the linkage pattern of mannose (see Fig. 1). 

Chromatographic analysis ages G.l.c. separation of substituent, partially methylated alditol acetates On-line e.i.- or c.i.-m.s. analysis G.l.c. analysis after sequential hydrolysis, reduction, and acetylation... 

Developments in capillary columns for GLC have improved the resolution of the individual components with a concomitant reduction of elution times. Neeser and Schweizer (1984) have separated the 0-methyloxime acetates of several sugars using a fused-silica Carbowax 20M capillary column. Although alditol acetates can be separated by capillary GLC (Blakeney et al., 1982), this method is more suitable for separating complex mixtures of partially methylated alditol acetates derived from meth-ylation analysis. It has been reported that phthalic esters interfere with the determination of alditol acetates by GLC (Dudman and Whittle, 1976) on conventional packed columns. This problem can be overcome to some extent by the use of capillary columns with polar phases (Henry et al.,... 

The use of alditol acetates for the separation of mixtures of partially methylated sugars not only simplifies the g.l.c. but also the mass spectra, because such compounds contain carbon to carbon bonds of only three types those between (a) carbon atoms that each carries a methoxyl group, or (b) each bears an acetoxyl group, or (c) adjacent carbon atoms having one substituent of each type. Mass spectrometry of partially methylated alditol acetates thus gives rise to relatively few primary fragments that are characteristic of the pattern of substitution. This technique was introduced to carbohydrate chemistry by Lindberg and his associates, and has been employed extensively by them in subsequent structural studies, some of which are discussed next others are listed in Table XXXI (see p. 103). 

The use of mass spectrometry in the structural analysis of carbohydrates, first reported in 1958 (114), was developed in detail by Kochetkov and Chizhov (115). They showed that, under electron impact, the acetylated and methyl ether derivatives of monosaccharides provided a wealth of structural information through analysis of typical fragmentation pathways of the initial molecular ion. This has proved of enormous utility in the structural elucidation of polysaccharides and complex oligosaccharides sequential permethylation, hydrolysis, reduction to the alditol, and acetylation, affords mixtures of peracetylated, partially methylated alditol acetates that can be separated and analyzed by use of a gas chromatograph coupled directly to a mass spectrometer (25). The mass spectra of stereoisomers are normally identical, while the gas chromatographic retention times readily permit differentiation of stereoisomers. 

Per-O-acetyl aldononitriles and methylated aldononitrile acetates have been separated by g.I.c. on a mixed liquid phase. Chemical ionization m.s. showed the presence of peaks at M + 1 in each instance. The retention times of a number of partially methylated alditol acetates have been recorded on a variety of stationary phases. Using a combination of silica gel chromatography and g.I.c., fifteen methyl ethers of methyl a-D-galactopyranoside have been isolated from the partial methylation products of D-galactose. ... 

Mixtures of O-methyl ethers obtained by partial methylation of a number of methyl glycopyranosides have been acetylated and the products identified by g.l.c.-m.s. The use of partially ethylated alditol acetates for the analysis by g.I.c. of the components of polysaccharides has been described. The ethyl analogues are eluted before the corresponding methyl derivatives, and this often allows the separation of many polysaccharide components by g.l.c. that are not separable as their partially methylated alditol acetates. The use of molar flame-responses calculated on the basis of effective carbon responses has been advocated for the accurate determination of partially methylated and partially ethylated alditol acetates by g.I.c. ... 

Partially ethylated alditol acetates may be used as alternative sugar derivatives when separation difficulties are encountered with particular combinations of the corresponding methylated compounds (74BMS263 75MI4). 

Many of the comments in Part I, Sections III (see Vol. 28, p. 23) and VII (p. 56) are equally pertinent to partially methylated alditols, which may be separated as their trimethylsilyl ethers, acetates, or tTi-fluoroacetates of these, the acetates are most generally used. 

Mass spectral data for the primary fragmentations of partially ethylated alditol acetates have been tabulated so as to allow easy reference in the identification of these polysaccharide derivatives. A newly developed, highly polar, capillary column gave improved separations of many ethylated alditol acetates when compared with the corresponding methylated derivatives. Results have been presented which demonstrate that the molar flame-responses of partially methylated and partially ethylated alditol acetates should be calculated on the basis of... 

A three-component, liquid phase used by Albershdm and coworkers for the separation of alditol acetates has also been found to give good resolution of partially methylated glucitols. ... 

Partially methylated derivatives of 2-deoxy-2-methylamino-D-glucose have been separated and identified as the corresponding alditol acetates by combined... 

Including a method for obtaining reproducible retention coefficients using two internal standards, and another paper describes over 242 such derivatives from eight alditols. The suitability of a variety of stationary phases for capillary separation of alditol acetates and their partially methylated analogues derived from neutral and amino-sugars has been investigated, while the separation of such compounds on packed columns has also been... 

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