Mass spectrometry methyl group cleavage

However in order to establish the position of unsaturation, it is necessary to prepare the dimethyl disulfide (DMDS) derivative. DMDS simply adds across a double bond to leave a CH3S- group attached both carbons. The presence of the methyl thioether groups on adjacent carbons renders the bond between them susceptible to cleavage during mass spectrometry, and hence it is possible to determine the position of the original double bond... 

When combined with mass spectrometry, GLC can confirm the identity of most of the closely related components of complex mixtures found in wax, cutin or suberin analysis. Examples of particular uses of this technique include the identification of branched fatty acids (Tulloch, 1976 Jackson and Blomquist, 1976), location of methyl branches in alkanes (Fig. 6.13), location of functional groups such as carbonyl and hydroxyl moieties on aliphatic chains following a-cleavage (Tulloch, 1976), and identification of wax esters (Kolattukudy, 1980). 

Combined glc and mass spectrometry provide the capability to deal with the complex mixtures of closely related compounds often found in plant cuticles. Even though identification of new compounds solely by their mass spectra cannot be considered reliable, mass spectrometry has become an invaluable tool in identifying known types of compounds in cuticular lipids. For example, methyl branches in alkanes can be located by cleavage on both sides of the substituted carbon (Fig. 5). Mass spectrometry is also the most suitable technique for identifying branched fatty acids (Tulloch, 1976 Jack-son and Blomquist, 1976 Nicolaides and Apon, 1977). Functional groups such as carbonyl groups and hydroxyl groups in the aliphatic chain can be... 

Unlike other members of this group, the DNA strand scission by C-1027 occurs without activation by a thiol or nucleophile [207, 208]. The formation of radical intermediates causing DNA cleavage by the antibiotic C-1027 was confirmed by spin trapping. The signals of the spin adducts with 2-methyl-2-nitrosopropane were recorded by ESR spectroscopy. The spin adducts were also detected by mass spectrometry (Scheme 3.1) [208]. It was shown that the antibiotic C-1027 is an equilibrium mixture of forms 3.407 and 3.410, the latter in very low concentrations. The process of hydrogen atom elimination from the DNA and the formation of aromatic structure 3. 411 were found to proceed in two steps first, slowly from atom C and then from atom C in a fast step [208, 209]. These data help us to understand the mechanisms of DNA strand scission by the antibiotic and thus contribute to the development of new anticancer drugs with specific delivery systems [208, 209]. Maduropeptin 3.408 is also able to form diradicals without activation [210]. 

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