5- Amino-4-imidazolecarboxylic acid

The well-known application of 2,4,6-tris(ethoxycarbonyl)-l,3,5-triazine as a diene in inverse electron demand Diels-Alder cyclizations was adapted for the synthesis of purines <1999JA5833>. The unstable, electron-rich dienophile 5-amino-l-benzylimidazole was generated in situ by decarboxylation of 5-amino-l-benzyl-4-imidazolecarboxylic acid under mildly acidic conditions (Scheme 54). Collapse of the Diels-Alder adduct by retro-Diels-Alder reaction and elimination of ethyl cyanoformate, followed by aromatization by loss of ammonia, led to the purine products. The reactions proceeded at room temperature if left for sufficient periods (e.g., 25 °C, 7 days, 50% yield) but were generally more efficient at higher temperatures (80-100 °C, 2-24 h). The inverse electron demand Diels-Alder cyclization of unsubstituted 1,3,5-triazine was also successful. This synthesis had the advantage of constructing the simple purine heterocycle directly in the presence of both protected and unprotected furanose substituents (also see Volume 8). 

Crosslinked polymers of vinyl-substituted imidazolecarboxylic acids have been studied as chelating resins for heavy metal ions (78MI11101). For example, polymer (75) displays stabilities and capacities in the order Cu2+ > Ni2+ > Cd2+ > Zn2+ > Mg2+ which is similar to that observed with other amino acid chelating resins. The unusual feature of the polymer, however, is that exceptionally strong complexing abilities are maintained even in strongly acidic media. Polymer (75) also displayed potential utility for the removal of mercury(II) ions from aqueous media. 

Reaction of 5-amino-l -benzyl-4-imidazolecarboxylic acid 495 with 2,4,6-tris(ethoxycarbonyl)-1,3,5-triazine 496 at 80 °C in DMF led to 9-benzyl-2,6-bis(ethoxycarbonyl)purine 501 in 83% yield. Presumably, 5-amino-l-benzyM-imidazole 497 is generated siVu from the acid and is highly reactive for the cycloaddition. The cycloadduct 498 then spontaneously undergoes retro Diels-Alder reaction with the loss of ethyl cyanoformate 499 followed by the loss of ammonia and aromatization to produce the purine in a regioselective manner (Scheme 114) <1999JA5833, 2005JOC998>. 

Representative procedure 2-Amino-4(5)-cyano-5(4)-imidazolecarboxylic acid (0.510 g, 3 mmol), anhydrous lithium chloride (0.5 g), pyridine (2 ml,... 

These organisms convert all of the purines they attack (uric acid, hypo-xanthine, guanine, and the nucleosides inosine and guanosine) to xanthine. Xanthine is hydrolyzed to 4-ureido-5-imidazolecarboxylic acid. A second enzyme that requires divalent cations splits the ureide to leave 4-amino-5-imidazolecarboxylic acid. The second step is inhibited by metal-chelating agents these were used to permit the product of the first enzyme to be accumulated and identified. Aminoimidazolecarboxylic acid is decarboxylated by a third bacterial enzyme, leaving 4-aminoimidazole. 

Photolytic conversion of the alcoholates of 5-diazouracil (238) into the corresponding imidazolecarboxylates (239) is very slow in neutral solution ca. 10— 15% conversion after 20 h) but is complete in 4—5 h when performed in a solution that is saturated with hydrogen chloride (Scheme 94). Triazoles (241) are formed by acid-catalysed rearrangement of the N-amino-barbituric acids (240 X = O or S) (Scheme 95). ... 

Methylated 4-amino-5-imidazolecarboxylate. Another peak characteristic of the urine of DPA-treated rats was also analyzed by GC-MS after the urinary amino acids were derivatized with... 

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