5-Amino-4-imidazole ribotide

AICAR, 5-d mitio-1-(S-O-phosphono-0-i>-ribo-juranosyil-IH-imidazole-4-carboxamide S-amino-l-ribo-juranosylimidazoie-4-carboxamide S -phosphate 5-amino -4-imidazo]ecarboxamide ribonucleotide 5-amino -4-imid-azolecarboxamide ribotide 5-amino-I-<5 -phosphofurano-ribosyl)-4-imidazolecarboxamide. C,H SN40,P mol wt 338.22. C 31.96%, H 4.47%, N 16.57%. O 37.85%, P 9.16%. Synthesis from AIR Lukens, Buchanan, J. Am. Chem. Soc. 79, [511 (1957) J. Biol. Chem. 234, 1791 (1959). 

AIR. /-(S-O-Phosphono-d-D-ribofuranosyl)-lH-imidazol-5-amine 5-amino-I-ribofuranosylimidazole S -phosphate 5-aminoimidazole ribonucleotide 5-aminoimida-zole ribotide 5 -amino -1 -(5 -phosphofuranoribosy] )imida -zole. C H14N307P mol wt 295-19. C 32.55%. H 4.78%, N 14.23%, O 37.94%, P 10.49%. An intermediate in the biosynthesis of purines. Synthesis from formylglycinamide ribonucleotide Levenberg, Buchanan, J. Biol Chem. 224, 1005 (1957) Lukens, Buchanan, ibid. 234, 1791 (1959). 

Amino-4-imidazole carboxamide ribotide is converted to 5-formamido-4-imidazole carboxamide ribotide in a formylation reaction using N -formyltetra-hydrofolic acid. The formylation is catalyzed by 5-aminoimidazole-4-carboxamide ribotide transformy-lase. Isonicase then closes the purine ring, forming inosinic acid in the absence of ATP. Fig. 3-59 illustrates the origin of each atom of the purine ring. 

Amino-4-imidazole carboxamide ribotide, a precursor only two steps removed (formylation and cycli-zation) from inosinic acid, can be synthesized by the direct condensation of the imidazole with 5-phosphori-bosyl pyrophosphate. The enzyme catalyzing this reaction was purified from an acetone powder of beef liver. The same enzyme (AMP pyrophosphorylase) catalyzes the condensation of adenine, guanine, and hypoxan-thine. Nucleoside phosphorylase is an enzyme that catalyzes the formation of a ribose nucleoside from a purine base and ribose-1-phosphate. Guanine, adenine, xanthine, hypoxanthine, 2,6-diaminopurine, and aminoimidazole carboxamide are known to be converted to their respective nucleosides by such a mechanism. In the presence of a specific kinase and ATP, the nucleoside is then phosphorylated to the corresponding nucleotide. 

As noted in Scheme 12.87, the early stages of purine biosynthesis involve the generation of 5-aminoimidazole ribotide [5-amino-2-(5 -phosphoribosyl)imidazole]. In vertebrates, carboxylation of 5-aminoimidazole ribotide (Scheme 12.96) is effected with carbon dioxide (CO2) under the influence of phosphoribosylaminoimidazole... 

Then as shown in Scheme 13.67 (a reproduction of Scheme 12.96), 5-aminoimidazole ribose 5-phosphate is carboxylated (either with CO2 or with bicarbonate) to 5-carboxyamino-l-(5 -phosphoribosyl)imidazole, which rearranges to 5-aminoimidazole ribotide-4-carboxylate, and the latter undergoes amination from aspartate (Asp, D) to yield 5-amino-l-(5-phosphoribosyl)imidazole-4-carboxamide after the loss of fumarate. Finally (Scheme 13.8), A-formylation is effected with lO-CHO-H, folate to yield the A-formyl derivative (5-formamido-l-(5 -phosphoribosyl)imidaz-ole-4-carboxyamide) and cyclization yields inosine 5 -phosphate (IMP). 

Amino-5-imidazole-carboxamide ribotide CoF + HCOOH C -formyl-CoF O... 

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