Aminopyrimidines, structure

More novel results were published in the area of the isomeric [l,2,4]triazolo[l,5-c]pyrimidine ring system. In Table 16, a few applications of earlier known methodologies are shown. All these compounds were synthesized by transformation of 4-imino-3-aminopyrimidine or analogous derivatives by reagents providing a one-carbon-atom structural unit (e.g., carboxylic acids or derivatives). 

Aminopyrimidines have been studied by Albert et al. (1948), and, by relying on the pAj-values at 20° of aminopyridines, there is no doubt that the 4-amino-derivative is protonated on the ring nitrogen N-1 (pAj = 5 69, as compared with pA = 1-23 for unsubstituted pyrimidine). The 2-amino-derivative is a weaker base (pAg = 3 45) and the 5-amino-derivative is weaker still (p/Cg = 2-60). An interesting ultraviolet spectral correlation has recently been pointed out (Albert and Taguchi, 1973) between compounds containing the 2-aminopyrimidinium and 2-pyrimidone structures ([59] and [60]). 

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. 

Having a cyano group and an amino group ortho to each other on a ring is another system that has led to the formation of fused pyrimidine ring systems. In this case, an aminopyrimidine is the result. Compound 42 in Scheme 5 is one such structure. Treatment of 42a with formamide leads to the amino derivative 43 <1999PS(155)175>. Alternatively 42b provides 44 after treatment with triethyl orthoformate followed by hydrazine <1999PS(155)175>. 

If the best donors and acceptors couple, and the common aminopyrimidine bidentate hydrogen bonds form, then the following acentric structure is conceivable. 

Aminopyrazines, like aminopyridines and aminopyrimidines, form p-aminobenzenesulfonyl derivatives, and one of these, 2-sulfanilamido-3-methoxypyrazine (11), is clinically used as an antibacterial agent.320 Bromination of compound 11 in methanol gives a product (114)321,322 which was originally incorrectly formulated as a hydrate.323 The correct structure follows from spectroscopic evidence and alkaline... 

Since 4-aminopyrimidine is known to exist predominantly in the amino form, with a double bond between N(3) and C(4), it bears some structural resemblance to adenine, which may be considered a formal analogue of a 5,6-disubstituted 4-aminopyrimidine, and (at least to some extent) of cytosine, which is 4-amino-2-oxopyrimidine (Table II). This pointed to the possible utility of a detailed examination of the electrochemical behaviour of 4-aminopyrimidine, and some of its methylated analogues. 

Fig. 39a, b Crystal structures of the capsule 52 between two tetracarboxylic acid resorcinarenes and four 2-aminopyrimidine molecules showing a the composition b the packing of the guests within the cavity (one aminopyrimidine is omitted to show interior)... 

The structure of the tetrahydropyrimidine has not been determined. 2-Aminopyrimidine is reduced similarly, but the dihydropyrimidine is not further reducible. 

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