V. I. Kadentsev

Abstract: The fragmentation pattern in electron-impact mass spectrometry has been established for the peracetylated methyl ester methyl glycoside derivative of N -acetylneuraminic acid. The resulting, data allow the interpretation of the mass spectrum of the corresponding derivative of a new sialic acid isolated from the starfish Distolasterias nipon which is shown to be 8- O -methyl- N -acetylneuraminic acid.

Abstract: The mass spectra of a series of hex-2-enopyranoside derivatives indicated that fragmentation of members of this class occurs by two general paths: ( i ) by loss of the substituents attached to C-1, C-4, and C-6, giving a series of cyclic ions related to pyran, and ( ii ) by retrodienic cleavage. Recognition of the ions produced by this latter mode can provide means for allocating the positions of double bonds in unsaturated carbohydrates, but since allylic rearrangements can, in some circumstances, precede fragmentations, care has to be taken in interpreting the spectra. The spectrumof 1,2,4-tri- O -acetyl-3-deoxy-β- d - glycero -pent-2-enopyranose indicates that isomerisation to 5,5,6-triacetoxy-5,6-dihydro-2 H -pyran occurs prior to fragmentation. Such an isomerisation has not been observed before with unsaturated sugars.

Abstract: Some esters of γ, δ-unsaturated or β-arylsubstituted acids undergo a peculiar transformation under electron-impact including an elimination of the alcohol residue as a radical R. with the following loss of the ketene molecule. One of the oxygen atoms of the carbonyl group enters an ion which is formed from an unsaturated part of the molecule. The possible mechanism of this reaction and the influence of structural modifications on the course of this process are discussed.

Abstract: The chemical ionization mass spectra of various aliphatic nitro compounds have been studied. Almost all the nitro compounds form stable [M+H]+ ions in sharp contrast to the instability of their ions produced by other ionization techniques. The fragmentations of the [M+H]+ ions are discussed, the mechanisms and structures of fragment ions proposed being supported by quantum mechanical calculations. Correlations between chemical ionization mass spectra and structures of compounds studied are outlined. Reliable identification of mono- and polynitroalkanes and some related derivatives may be made by analysis of their chemical ionization mass spectra.

Abstract: α,β-Unsaturated aldehyde acetals add :CCl2 (obtained in accordance with Makosza procedure) to form gem-dichlorocyclopropanecarboxaldehyde acetals (1) in high yields when the ratio of reactants is no less than 1:4. The addition of :CCl2 to polyunsaturated aldehyde acetals in the above conditions proceeds regioselectively at double bonds enriched by electrons. Compounds 1 are reduced by sodium in liquid ammonia to give cyclopropanecarboxaldehyde acetals (2). Both 1 and 2 are hydrolized by dilute H3P04 to the corresponding aldehydes and are added to vinyl ethers in the presence of BF3·Et2O to produce only 1:1 adducts which are hydrolyzed by a mixture of AcOH-AcONa-H2O to give β-formylcyclopropanes which were previously unknown.

Abstract: Publisher Summary This chapter discusses the chemistry, metabolism, and biological functions of sialic acids. Interest in the sialic acids has rapidly increased in recent years, especially because of the reorganization of their involvement in the regulation of a great variety of biological phenomena. The occurrence of sialic acids in plants has never unequivocally been established, although some positive reports exist. The acylneuraminic acids can be released from their glycosidic linkages either by dilute (aqueous or methanolic) acids or sialidases. The unequivocal determination of sialic acids occurring in low concentrations in many biological materials is rather difficult, and this explains the many errors that have been made in this field. The biosynthesis of N-acetylneuraminic acid (Neu5Ac) is briefly reported in this chapter and more attention is given to the enzyme reactions modifying this compound. Little information is available about the role of the modifications of sialic acid resulting in a species- and tissue-specific distribution of different N,O-acylated and O-methylated sialic acids.

Abstract: Publisher Summary This chapter describes that mass spectrometry (m.s.) has become an important and versatile technique in carbohydrate chemistry. The chapter deals with m.s. as a tool in the structural analysis of naturally occurring carbohydrates. The mass spectra of permethylated methyl glycosides show ions derived from a number of specific degradation pathways. These fragmentations have been carefully studied in the chapter, by using deuterium-labelling techniques. Direct derivatization of reducing sugars by permethylation, peracetylation, or per( trimethylsilyl )ation gives a mixture of glycosides. These derivatives are suitable for g.1.c. analysis, although, for complex mixtures of sugars, the multiplicity of peaks caused by the derivatization may complicate elucidation of the results. The partially methylated sugars are separated and converted into the methyl glycosides, and these are methylated with trideuteriomethyl iodide. The substitution pattern of the trideuteriomethyl groups can be determined by m.s., and the nature of the sugar ascertained by g.1.c. (by comparison with the permethylated compound used as the reference sample).