Mass spectrometry of thio analogues of pyrimidine bases: Correlation of the intensities of the M^+˙ and selected fragment ions of o‐(m‐ and p‐)substituted benzylthiouracils

Abstract

The mass spectral fragmentations of sixteen new 2-and 4-o-(rn-and p-)substituted benzylthiouracils and o-(rn-and p-)substituted 2,4-dibenzylthiouracils with NO, and CI substituents in the benzyl groups were investigated. Fragmentation pathways are proposed on the basis of accurate mass and metastable transitions measurements. The correlation between the abundances of the M" and the selected fragment ions of investigated compounds is discussed. The data obtained create the basis for distinguishing structural isomers.

Electron impact mass spectral study of 1,2‐di‐o‐(m‐ and p‐)nitro‐(bromo‐)benzyl‐2‐thio‐6‐methyluracils and 1,2‐di‐o‐(m‐ and p‐)nitro‐(bromo‐)benzyl‐2‐thio‐5‐bromo‐6‐methyluracils

“…It should be emphasized that such cleavages of bonds of the uracil ring of 2-benzylthiouracils have not been observed in the mass spectrometric fragmentations of these compounds. 13 As shown in Scheme 2 and Table 2, the principal mass fragmentation pathways of the molecular ions of 1,2-di-o-(m-and p-)nitro-(bromo-)benzyl-2-thio-5-bromo-6-methyluracils 7-12 are similar to those of 1-6, discussed above. The inductive cleavages of proceeds with elimination of a X-C 6 H 4 -CH 2 -S .…”

“…[8][9][10][11] Recently, we reported the mass spectral behaviour of new metameric 2-alkoxycarbonylalkyl-2-alkoxycarbonylalkylthio-6-aminouracils. 12 Previously, we had also reported the mass spectral fragmentations of 2-and 4-o-(m-and p-)chloro-(nitro-)benzylthiouracils and 2, 4-dio-(m-and p-)chloro-(nitro-)benzylthiouracils, 13 as well as of 2-o-(m-and p-)chloro-(bromo-and nitro-)benzylthio-5-bromo-6-methyluracils.…”

“…This investigation was also undertaken to discover whether it is possible to differentiate within the isomeric sets of o-(m-and p-)nitro-and -bromo-substituted dibenzyl derivatives of 6-methyl-2-thiouracil and of 5-bromo-6-methyl-2-thiouracil on the basis of electron impact (EI) mass spectrometric analysis. This aspect was approached via comparisons of the values of m (ratios of intensities of selected fragment ion peaks to that of the corresponding molecular ion peak 12,13 ). The compounds 1-12 were obtained and structures confirmed according to the literature.…”

New isomeric 2‐ortho‐(meta‐ and para‐) chloro‐(bromo and nitro‐)benzylthio‐6‐aminouracils

“…the abundances of the selected evenelectron fragment ions relative to the abundances of the molecular ions. It has been established by us previously [4] that differences in the values of the coefficients µ are useful for differentation of the positional isomers of 2-and 4-substituted alkylthiouracils [16], as well as benzylthiouracils [3,4]. For compounds 1-9, Table 8 As can be seen from the data in Table 8, the differences between the relative intensities of the peaks of selected fragment ions and M +.…”

Electron ionization induced mass spectral study of 2‐alkylthio‐ and 4‐alkykthio‐5‐bromouracils

“…15,16 Electron ionization mass spectrometry (EI-MS) was used to determine the location of the sulphur atom in the uracil ring or the positioning of a substituent on the nitrogen atoms N-1 or N-3. 17,18 The correlation between selected fragment ions and molecular ion abundance in benzylthiouracils, 19 2-alkylthiouracils, 20 and thiazolo-[3,2-a]-and [3,2-c]pyrimidin-5-ones 21 has been thoroughly studied in our laboratory. The fragmentation of 2-and 4-thio-5-bromouracils alkylated on the sulphur atoms has not, however, been studied.…”