Analysis of polysaccharide and antibiotic compounds

The conventional mass spectra obtained from saccharides transformed into their OTMS and -OCH3 derivatives were interpreted by using labeled derivatives. Systematic studies had never been performed on -OAc derivatives. However, in 1975, Das and Thayumanavan [230] studied various peracetylated disaccharides by their IKE spectra to resolve the ambiguity appearing in the El mass spectra of the isomeric peracetates of trehalose, sophorose, kojibiose, laminaribiose, maltose, melibiose and gentiobiose, all characterized by the same molecular weights (678). 

The conventional mass spectra indicate no significant difference between melibiose (1 - 6) and gentiobiose (1 - 6), whose structures differ only by the stereochemistry of the disaccharide bond and of one OH group. 

Ratios of characteristic fragment ions measured in the conventional El mass spectra of various isomers [230] 

These spectra indeed correspond to veritable fingerprints , sensitive to stereochemical differences. Their disadvantage, however, is related above all to the ambiguity of the indicated transitions, since they represent mass ratios mJmY, for which several solutions are possible. 

Among the highest mass peaks, certain are due to the toss of acetic acid, and the consecutive decompositions of this [M-CH3COOH] ion are difficult to study. It may indeed be produced from any modified -OH group, and so this peak may represent a mixture of isomeric structures. The ability to study the behavior of the unique structure molecular ion itself may be more valuable and lead to a greater quantity of data. Chemical ionization, enabling these ions to be studied in their protonated (or not) form, may thus be an alternative to El. 

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