Trimethyl uric acid

In addition to the intramolecular effects, steric factors are of considerable influence. The most usual one consists of steric hindrance to attack on the lactam nitrogen atom. Certain examples of this will be given. By comparison with uracil, it would be expected that uric acid (10) would be iV-methylated in the pyrimidine ring, but that in the imidazole ring 0-methylation should also be possible. However, the experiments of Biltz and Max show that all uric acid derivatives which carry a hydrogen atom in the 9-position are converted by ethereal diazomethane into l,3,7-trimethyl-8-methoxyxanthine (11). The following are examples uric acid and its 1-methyl, 3-methyl, 7-methyl, 1,3-dimethyl, 1,7-dimethyI, 3,7-dimethyl, and 1,3,7-trimethyl derivatives. Uric acid derivatives which arc substituted by alkyl groups in the 3- and 9-positions (e.g., 3,9-dimethyl-, 1,3,9-trimethyl-, and 3,7,9-trimethyl-uric acid)do not react at all with diazomethane, possibly because of insufficient acidity. Uric acids which are alkylated... 

Figure 26. Proposed primary electrode reactions for the peak electrochemical oxidation of N-methylated uric acids. The cyclic voltammograms are, from top to bottom, uric acid, 1,3,7-trimethyl uric acid and, 1,3,7,9-tetramethyl uric acid in phosphate buffer, pH 7, at a RPGE at 200 mVs ...

Uric acid, 8-ethoxy-1,3,7-trimethyl-rearrangement, 5, 534 Urie acid, methyl-reduction, 5, 541 Uric acid, 7-methyl-synthesis, 5, 582... 

Uric acid, 9-methyl-2,8-dithio-, 5, 590 Uric acid, 9-phenyl-synthesis, 5, 577 Uric acid, 8-thio-synthesis, 5, 577, 582 Uric acid, 1,3,7-trimethyl-ethylation, 5, 534 methylation, 5, 535 Uric acid, 1,7,9-trimethyl-methylation, 5, 535 Uridine... 

As indicated in Fig. 25-18, free adenine released from catabolism of nucleic acids can be deaminated hydrolytically to hypoxanthine, and guanine can be deaminated to xanthine.328 The molybdenum-containing xanthine oxidase (Chapter 16) oxidizes hypoxanthine to xanthine and the latter on to uric acid. Some Clostridia convert purine or hypoxanthine to xanthine by the action of a selenium-containing purine hydroxylase.3283 Another reaction of xanthine occurring in some plants is conversion to the trimethylated derivative caffeine. 328b One of the physiological effects of caffeine in animals is inhibition of pyrimidine synthesis.329 However, the effect most sought by coffee drinkers may be an increase in blood pressure caused by occupancy of adenosine receptors by caffeine.330... 

Accordingly, uric acid appears as 2, 6, 8-trioxypurin, and caffeine as 1, 3, 7-trimethyl-2, 6-dioxypurin ... 

Alkylation of uric add with diazoalkanes has been reviewed (32JPR(134)310). With uric acid 1,3,7,9-tetramethyluric add is produced, presumably via an intermediate alkoxy derivative (21ZPC(117)23) since 1,3,7-trimethyluric add and 1,7,9-trimethyluric add with diazomethane at room temperature furnished 8-methoxy-l,3,7-trimethyl and 2-methoxy-... 

---