5- Azauracil properties

It should be mentioned that a similar comparison of the dissociation constant values of uracil monoalkyl derivatives does not permit the determination of the sequence of dissociation on account of the small differences between the pEo values. However, the pH dependence of the XJV spectra showed that the first dissociation of uracil occurs at the NH group in position 1 and thus differently than in 6-azauracil. This, together with different acidity, represents the main differences between the properties of uracil and its 6-aza analogs. 

Acetylation of 6-azauracil thus proceeds in the same way as the acetylation of uracil and the properties of the acetyl derivatives are also roughly identical. 

The biochemical properties of l,2,4-triazine-3,5-dione (6-azauracil 12), 6-methyl-1,2,4-triazine-3,5-dione (6-azathymine 13), 2-G3-D-ribofuranosyl)-l,2,4-triazine-3,5-dione (6-azauridine 14) and 2-G3-D-deoxyribofuranosyl)-6-methyl-l,2,4-triazine-3,5-dione (6-azathymidine 819) have been extensively studied and various uses proposed (78HC(33)189,... 

Very few compounds containing the 1,2,4-triazine moiety are found as natural materials, such as the pyrimido[5,4-c]-1,2,4-triazines, fervenulin (2),265 reumycin (3),265 toxoflavin (4) and MSD-92 (5).441 A large number of synthetic 1,2,4-triazines have biological activity and have been used for various purposes. Thus, 1,2,4-triazines can be considered as azapyrimidines and thus a large number of 6-azapyrimidine nucleotides and nucleosides have been prepared and their properties studied intensively, for example 6-azauracil (6), 6-azathymine(7), 6-azacytosine (8), 6-azauridine (9),442 and 6-azacytidine (10).443... 

Since 1,2,4-triazines can be considered as azapyrimidines, a great number of 6-azapyrimidine nucleotides and nucleosides have been prepared and their properties intensively studied. Most significant amongst these are 6-azauracil (1), 6-azauridine (2), 6-azathymine (3), 6-azacytosine (4) and 6-azacytidine (5). 

The first chemical synthesis of these substances, using a procedure which yields 1-ribofuranosyl derivatives by pyrimidine bases, was described by Hall. By using the mercuric salt of 6-azathymine and tribenzoate of D-ribofuranosyl chloride, he obtained a mixture of two raonoribosyl derivatives and a diribosyl derivative. He determined the structure of the 3-substituted derivative by the similarity of spectra and other properties to those of 3-methyI-6 azauracil. The structure of the 1-ribosyl derivative was then determined from the similarity of the spectra with 6-azathymine deoxyriboside obtained enzymatically. 

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