Pyrimidine mass spectra

Beynon et al. have reported that the energy release during the decomposition of metastable peaks in the mass spectrum of 1,3,5-triazine was 187 peV, a lower value than for either pyridine or pyrimidine <710MS(5)229>. 

The mass spectrum of formycin (54a) showed M+ and MH+ ions due to the protonated base moiety of the molecule <78MI 712-01). The mass spectra of 5-substituted oxazolo[4,5-d]pyrimidines (78) proceeds via loss of the C-5 substituent <82KGS1255>. The main fragmentations of substituted imidazo[4,5-/>]pyrazines (79) <89KGS532> and oxazolo[5,4- have been determined. 

At one time the idea of recording a mass spectrum of a nucleic acid would have been considered utopic and futuristic. Nucleic acids are practically nonvolatile and usually possess a molecular weight of several million atomic mass units (amu) (fi) often expressed in daltons up to 10 daltons where 1 dalton = 1.67 X 10 g. They possess their own mass spectra. In general they are esters of phosphoric acid and polyols, such as the sugars ribose and 2 -deoxyribose, which are themselves substituted with heteroaromatic purine or pyrimidine bases. Consequently, fragment ions characteristic of all these structural elements can be found in the mass spectra of nucleic acids. 

A typical thermospray ionization mass spectrum for a sulfonylurea contains a weak protonated molecular ion and three to four characteristic fragment ions. Figure 2 shows the thermospray positive ion mass spectrum for HARMONY. The spectrum contains a protonated molecular ion at m/z 388, the sulfonamide ammonium adduct ion at m/z 239 and the protonated triazine urea fragment ion at m/z 184. At the same time, Figure 3 shows the positive ion thermospray mass spectrum for LONDAX. It contains the protonated pyrimidine amine at m/z 156, the protonated pyrimidine urea is at m/z 199 and the sulfonamide ammonium adduct ion at m/z 247. LONDAX (bensulfuron methyl) is a sulfonylurea rice herbicide and it elutes between EXPRESS and CLASSIC if we use the LC conditions outlined in Figure 1. HARMONY and LONDAX thermospray spectra were generated with the thermospray vaporizer tip temperature at 150°C and the source block temperature at 320°C. 

Kato et al.19 compared the mass spectra of 2-methyl-4-oxo-4/7- and 4-methyl-2-oxo-2//-pyrido[l,2-a]pyrimidines. Fragments at m/e = 120 and 92 appeared only in the spectrum of the 2-oxo isomer. In the spectrum of the 4-oxo isomer the peak at m/e = 105 corresponds to a single fragment of composition C6H5N2, whereas for the 2-oxo isomer, it is a mixture of two fragments, C6H5N2 and C7H7N. 

For example, full-scan mass spectra of buspirone contain an abundant [M+H]+ ion signal with little detectable fragmentation. The product ion spectrum reveals product ions and neutral losses associated with diagnostic substructures of buspirone (Figure 6.25). The product ion at mlz 122, for example, is indicative of the pyrimidine substructure. The presence of this ion in the product ion spectrum of a metabolite indicates a structure that contains the pyrimidine substructure. Similarly, the mlz 180 product ion is diagnostic of the azaspirone decane substructure, and the neutral loss of 164 (producing the mlz 222 product ion) is diagnostic of the butyl azaspirone decane dione substructure. 

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