Acetolysis, structural analysis

Notable progress in the structural analysis of methylene derivatives of the polyhydric alcohols resulted from the investigations of Hann, Hudson and their co-workers26 80,40-4 into the behavior of these compounds during acetolysis. It was found that a mixture of acetic anhydride, acetic acid and 1-2% sulfuric acid ruptures preferentially any methylene bridge which spans a primary and a secondary position, giving the acetate ester of the primary hydroxyl and the acetoxymethyl ether of the secondary hydroxyl subsequent treatment with sodium methoxide removes each of these substituents. Under similar conditions, the acetolysis of a benzylidene compound results in the replacement of the arylidene residue, wherever it is located in the molecule, by two acetyl groups.16 29 47 48... 

The complete structures of the oligosaccharides from these antigens were elucidated by using FAB-MS, NMR, acetolysis, and methylation analysis. Further key experiments performed by Hunter et al.st involved partial acid hydrolyses of... 

Part of the mannoprotein structure, as found in the yeast Saccharomyces cereviseae [80] contains a series of unbranched oligosaccharide chains of degree of polymerisation (d.p.) 1-5, with a(l-2) and a(l-3) linked Man residues, that are a-glycosidically linked to the OH of serine or threonine in the polypeptide, and which can be released by base catalysed P-elimination. Methods of determination of structures of oligosaccharides have included n.m.r. and mass spectrometry, deacylation with hydrazine, sequential glycosidase hydrolysis, partial enzymic and acidic hydrolysis and acetolysis, poiarimetry and methylation analysis. 

If the latter is true, the acetolysis pattern would be essentially unchanged before and after enzymolysis. Methylation analysis of the mannanase-resistant core, described above also supported the former structure. 

A small molecular weight oligosaccharide (16) attached separately at two sites near the A-terminus of bovine rhodopsin has been examined by a combination of methylation analysis, acetolysis, and enzymic studies. This structure is identical to a proposed intermediate in the biosynthesis of complex L-asparagine-linked oligosaccharides. Three oligosaccharides have been released from bovine rhodopsin by hydrazinolysis. One of the components has an identical structure to (16) except for the absence of the L-asparagine residue, and structures [(17) and (18)] were established for the other two oligosaccharides. 

An interesting transannular cyclization was uncovered by Helmlin-GER and Ourisson (772) who found that mere chromatography of bromo olefin (777) over silica gel (but not alumina) gives the cyclized product (172). Acetolysis of (171) gives both (172) and (173). Structure (172) is fully secured by an X-ray crystallographic analysis study (113). 

The complete structures of the carbohydrate units of three other glycopeptides from ovalbumin (62—64) have been established, using a combination of sequential digestion with glycosidases. Smith degradation, selective acetolysis, and methylation analysis. ... 

Figure 17. Structural model of LAM and AG. AG is drawn without the mycolic acids attached to the terminal Ara residues. The molecular weight of LAM has been determined by M ALDI-TOF on both native and permethylated samples. The arabinan circle in both LAM and AG represents structural details not yet defined. Detailed characterizations of the various arabinan motifs were based on MS/chemical analysis of fragments obtained through acetolysis, mild acid hydrolysis and endoarabinase digestion as indicated. The branched Ara6 motif is common to both AG and LAM whereas the linear Ara4 terminal motif is found only on LAM. An Ara22 motif as drawn is deduced to be present on AG [15],...

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