Mass spectra of carbohydrate derivatives

Unfortunately, owing to the extreme instability of the carbohydrate molecule, the molecular ion can only occasionally be traced in the mass spectra of carbohydrate derivatives. 

III. Mass Spectra of Carbohydrate Derivatives 1. General Remarks... 

A number of reviews of mass spectra of carbohydrates have been published from which references to the original papers are available (4, 9, 11, 24, 26). The application of mass spectrometry to this field was initially limited by the relatively low volatility of free carbohydrates and by the complex spectra obtained from some derivatives. These limitations have been partially overcome by new inlet techniques and by pioneering studies on classes and derivatives in order to understand the characteristic fragmentations and rearrangements of the molecular ions of a wide range of carbohydrates. 

O-Isopropylidene derivatives of carbohydrates form structural isomers from carbohydrates which themselves are epimers. Since structural isomers often fragment differently whereas epimers do not, mass spectra of these derivatives may permit interpretation in terms of stereochemistry. Although molecular-ion peaks are not observed, the molecular weight can be determined readily from a relatively intense M-CH/ peak, resulting from loss of a methyl radical from a 1, 3-dioxolane ring (12). 

The interpretation of the mass spectra of oligosaccharide derivatives follows the general principles that have been elaborated for simple cyclic and acyclic carbohydrates (66MI1 74MI1). 

The mass spectra of TMS derivatives of nucleosides selectively labelled with deuterium and oxygen-18 have been recorded.The position of chlorine atoms in the carbohydrate ring of chloro-deoxy-nucleosides can be established from their mass spectrum. 

Diethyl dithioacetal derivatives of carbohydrates are generally crystalline compounds which are easily prepared from sugars in the combined or free form. In contrast to the mass spectra of the carbohydrate derivatives discussed above, the mass spectra of diethyl dithioacetals allow direct determination of molecular weight from molecular-ion peaks of... 

The volatility of the trimethylsilyl derivatives of the aldonolactones and related carbohydrates has made these derivatives suitable for use in mass spectrometry.161,162 Petersson and coworkers161,162 reported the mass spectra of a variety of trimethylsilyl derivatives of aldonolactones, including the spectrum of 54. 

The mass-spectral method was first applied to carbohydrate derivatives in 19f>8, when Reed and coworkers5 reported the mass spectra of D-glucose,... 

Finally, the mass spectra of acyclic carbohydrate derivatives will be considered in many aspects, these differ essentially from those of the cyclic forms. 

Mass spectra have been measured for ketose acetates only,16 and the most characteristic feature of these mass spectra is the formation of a new series of fragments having no analogy in the mass spectra of other types of carbohydrate derivatives. 

It appears that mass spectrometry is of considerable value in structure determination although, at present, it is not possible to differentiate between 2- and 4-substituted isomers. The technique has been used to establish the structure of 4-(imidazol-4-yl)butane-1,2,3-triol55 which, unlike most carbohydrate derivatives, shows a molecular ion. The mass spectra of 2-alkylbenzimidazoles246 and mercaptoimidazoles124 have been examined, while use has been made of mass spectrometry in the identification of some alkyl, aryl, and acyl imidazoles.138... 

Application of mass spectrometry to carbohydrate derivatives has been reviewed in this Series. Although no example of its application to sugar sulfonates was cited, such experiments have undoubtedly been performed samples having very low volatility may be examined after direct introduction into the ion-source chamber. Sulfonates of 6-chloro-6-deoxy sugars were first identified in this way, and interpretation of the mass spectra was aided by the presence of fragments containing C1 and C1. 

Spectra, infrared, of carbohydrates, 12,13-33 Spectrometry, mass, of carbohydrate derivatives, 21,39-93 Spectroscopy, infrared, and carbohydrate chemistry, 19,23-49 Sphingosines, conjugates with sugars, 24, 381-433 Starch,... 

Direct derivatization of reducing sugars by permethylation, peracetyl-ation, or per( trimethylsilyl)ation gives a mixture of glycosides. These derivatives are suitable for g.l.c. analysis, although, for complex mixtures of sugars, the multiplicity of peaks caused by the derivatization may complicate elucidation of the results. The mass spectra of glycosides have been extensively studied, especially as peracetylated or permethyl-ated derivatives. In this article, these studies will be only briefly summarized. Recent developments and applications to studies of natural carbohydrates will, however, be discussed. 

Much of our knowledge on the fragmentation patterns of carbohydrate derivatives arises from studies on methylated monosaccharides, but in structural investigations, such compounds are seldom subjected to mass spectrometry. On the other hand, the molecular weight of a permethylated oligosaccharide is significantly less than that of the per(trimethylsilyl) derivative. For this reason, the mass spectra of disaccharides as -their permethylated alditols have been determined by Chizhov and coworkers, Karkkainen, and Krone and Beckey. Trisaccharides have also been studied by Karkkainen, either as permethylated glycosides or as alditols. ... 

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. 

Bowie JU, Gray GR (1984) Synthesis and mass spectra of partially methylated and partially ethylated anhydro-D-mannitol acetates derived by reductive cleavage of permethylated and perethylated saccharomyces cerevisiae D-mannans. Carbohydr Res 129 87-97... 

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