Methylation alditols

Glycosyl-linkages were determined by GC-EIMS of the partially methylated alditol acetates. RG-II samples (2 mg) were methylated using sodium methyl sulfmyl carbanion and methyl iodide in dimethyl sulfoxide [24] followed by reduction of the uronosyl groups with lithium triethylborodeuteride (Superdeuteride , Aldrich) [23,25]. Methylated and carboxyl-reduced samples were then submitted to acid hydrolysis, NaBIlt reduction and acetylation, partially methylated alditol acetates being analysed by EIMS on two fused-silica capillary columns (DB-1 and DB-225) [20]. 

Methylation analysis of PI and FIbp. The fractions were methylated according to Ciucanu and Kerek [8]. The procedure was repeated until no absorbance was detected by I.r. at 2500-3500 cm-i and the per-O-methylated polysaccharides hydrolyzed and analyzed by GLC and GLC-MS of the derived partly O-methylated alditol acetates. 

Carboxyl redution. A sample of pennethylated PI (5 mg) was carboxyl-reduced by a modification of the method described by Lindberg and Lbnngren [9], as follows. The methylated fraction was solubilized and added a mixture of LiAlH4 (25 mg) in THF (5 mL) at 20 °C for 4 h. and refluxed during 1 h. The excess of reagent was destroyed with ethyl acetate (5-6 drops) and water (10 drops) and the pH of the mixture adjusted to neutrality with acetic acid. The insoluble residue was removed by centrifugation. The reduced fi action was precipitated with EtOH. The reaction was monitored by l.r. specroscopy. Hydrolysis products were analysed by GC-MS as methyl alditol acetates... 

The removal of arabinose suggested the presence of peripheric a-L-arabinofuranosyl units. Flap was methylated by the method of Ciucanu and Kerek and products of derived O-methyl alditol acetates analysed by GLC-MS... 

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. 

The chemical-ionization (c.i.), mass spectra of some methylated alditol acetates have been reported.51,52 The main intensities in the c.i. 

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). 

Fig. 1.—Mass Fragmentograms of Partially Methylated Alditol Acetates Obtained from Rat-brain Glycopeptides. [(A) Fraction A glycopeptides, (B) fraction B glycopep-tides, and (C) fraction C glycopeptides. Peak 1, 2,3,4-tri-O-methylfucitol peak 2,...

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... 

The separation of fully methylated alditols has been investigated by Ovodov and Evtushenko,231 but is not suitable for routine use, because of the time necessary for the preparation of such derivatives, and the lack of resolution. 

Adapted from Kariya et al. (1997). With permission from Elsevier Publisher. a Partially methylated alditol acetate with methoxy groups at the positions shown. b Retention time on a SP2330 capillary column relative to 2,3,4-tri-O-methyl-fudtol. c The molar ratios were based on the peak area. d Not detected. 

The proposed structure is in full agreement with the results obtained by mass spectrometry, immunodiffusion and analysis of partially methylated alditol acetates (4). 

Figure 1. Methylation linkage analysis of PSL-I by GC/MS total ion chromatogram of partially methylated alditol and myoinositol acetates (PMAA) from PSL-I carboxyl-reduced trisaccharide by gas chromatography /mass spectrometry in...

Methylation linkage analysis of the partially methylated alditol acetates gave the following derivatives ... 

Figure 9. Open tubular gas chromatogram of partially methylated alditol acetates obtained from blood-group A active tetraglycosylceramide (A) and hexaglycosyl-ceramide (B), respectively. Stationary phase was OV-1, and carrier gas was Ns. Column temperature was kept at 175°C for 14 min, then raised l°C/min. The designation above the peaks indicate actual binding positions.

Partly methylated alditols can be acylated after their conversion into TMS ethers [408]. Non-polar stationary phases of the OV-101 and SE-30 types are the most suitable for the separation of these derivatives. 

E. Lau and A. Bacic, Capillary gas chromatography of partially methylated alditol acetates on a high-polarity, cross-linked, fused-silica BPX 70 column,./. Chromatogr., 637 (1993) 100-103. 

Proton NMR spectra of Xlyoglucans and GC-EIMS of methylated alditol acetates. 

Primary fragment ions from partially methylated alditol acetates (Fig. 2) arise by -cleavage with, in general, preferred formation of ... 

Fig. 2. Primary fragment ions arising by a-cleavage in the mass spectra of partially methylated alditol acetates.

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