Mass spectra of pyrimidines

The mass spectra of pyrimidines and quinazolines are generally simple and of no great interest, factors which account for the paucity of data available (B-71MS468). 

The mass spectra of l,2,4-triazolo[4,3-a]pyrimidines showed, mainly, their molecular ion peaks [83S44 88JCS(P1)351 94LA1005]. The mass spectra of l,8a-dihydro-l,3,7-trisubstituted-l,2,4-triazolo[4,3-a]pyrimidines 41 revealed a common peak of the nitrileimine 159 (94LA1005). 

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. 

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. 

Very similar degradation routes are reported for pyrimidines.171 A preliminary report on the mass spectra of nucleosides has been given by Biemann.172 Key fragments are produced by rupture of the... 

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. 

Finally, the desorption chemical ionization (DCI) mass spectra of several synthetic nucleosides, mostly in the pyrimidine series, have been recorded. The potential application of protonated or cationized (NH4 ) molecular ions and bases for the detection of these nucleosides has been demonstrated. One of the important features of these spectra is the presence of [ B + H ] and/or [B -f- NHJ ions, which confirms the previously described general fragmentation scheme. In desorption chemical ionization studies (which describe in-beam experiments in a Cl source), the desorption of intact molecules, followed by ionization, is often confused with the desorption of preformed ions. Slow hydrolysis within a Cl source leads to intense ions (e.g., [BH]" ) such as those observed for nucleosides, as well as for intact DNA. ... 

The electron impact mass spectra of a number of the tricyclic 5-substi-tuted-9-methyl- l,2,4-triazolo[4,3-c]tetrazolo[l,5-a]pyrimidines 131 were reported (790MS227). Tricyclic intermediates were proposed to explain the mass spectral fragmentation of the 8-allyl-5-benzyl-7-methyl-l,2,4-triazolo[4,3-c]pyrimidine 132 (93KGS1545). 

Brown DJ, Waring P (1978) Pyrimidine reactions. XXVII. Syntheses, reactivities and mass spectra of some 2-isopropylpyrimidine derivatives. Aust J Chem 31 1391-1395... 

In addition, we should note that data of H, NMR spectroscopy, mass-spectra, and elemental analysis given in [138] did not contradict the structure of compound 98, being regioisomer of 97. The similar situation had already been shown in the synthesis of 3-aminoimidazo[l,2-a]pyrimidines [139]. Mandair et al. carried out the model MCRs of 2-aminopyrimidine with several aldehydes and isonitrile components in the methanol under the ambient temperamre with the various catalysts. As a result, 3-aminoimidazo[l,2-a]pyrimidine and position isomeric 2-aminoimidazo[l,2-a]pyrimidines were isolated from the reaction mixture in different ratio (Scheme 45). The stmctures of the isomers obtained in this case were confirmed by the X-ray diffraction analysis, as well as the structures of the side-products isolated. 

UV resonance Raman spectra of chemical analogues of the pyrimidine nucleobases have been recently reported. Billinghurst et al. [142] have recently reported the UV resonance Raman intensity-derived excited-state stmctural dynamics of 5-fluorouracil, and have shown them to be essentially identical to those of thymine. In that paper, they also report the UV resonance Raman spectra of 5-chlorouracil, 5-bromouracil, and 5-iodouracil, and show that the spectra all are similar. By extension, they argue that the excited-state stmctural dynamics of the 5-halouracils are all similar to each other and to those of thymine, supporting their model that the excited-state structural dynamics of uracil and thymine nucleobases are dictated by the mass of the substituent at the 5 position. 

Mass spectra The mass spectra and fragmentation pattern of thieno[2,3-d]pyrimidine-2,4-diones (85JHC889) and thieno[3,4-d]pyrimidine-2,4-diones have been reported (91MI3). 

---