4- Aminopyrazolo 3,4-d pyrimidines

The enzymatic conversion of many analogues of the naturally occurring purines directly to their biologically active form, the ribonucleotides, in vivo [5, 8, 10, 13, 39] underlines the importance of these enzymes to the drug action of this class of compounds. 2-Aminoadenine (2, 6-diaminopurine, I) [107], 2-fluoroadenine (II) [108], 4-aminopyrazolo [3, 4-d] pyrimidine (VIll) [109]. and 2- and 8-aza-adenine (IX and X) [ 110, 111] have all been shown to be substrates for the adenine phosphoribosyltransferase [J12, 113]. Extensive studies on the metabolism of 2-aminoadenine (I) in E. coli [114, 115], L cells [116], and mice [117] have also shown its conversion by this enzyme to the ribonucleotide. 

Conversion of 4-aminopyrazolo [3,4-d] pyrimidine (VIII) to its ribonucleotide by mouse tumours and host tissues has been observed [118,119]. Although no evidence of the anabolism of A -methyladenine (111) [120] to the ribonucleotide was obtained in mice with Ehrlich ascites carcinoma [121, 122], it is anabolized by bacteria [123. 124] and the enzyme responsible was partially purified from Salmonella typhimurium [125]. Human epidermoid carcinoma No. 2 cells resistant to 2-fluoroadenine (H.Ep.-2/FA) have lost adenine phosphoribosyl-... 

Although demethylation, which occurs in the liver, is normally considered to be a catabolic process, it may result in conversion of an inactive form of a drug to the active form. Thus 6-(methylthio)purine (XXXIX) is demethylated by the rat to 6-mercaptopurine [205]. This demethylation occurs in the liver micro-somes and is an oxidative process which converts the methyl group to formaldehyde [204, 207]. The 1-methyl derivative of 4-aminopyrazolo[3,4-d] pyrimidine (XLI) is demethylated slowly, but 6-mercapto-9-methylpurine (XLII) not at all [208]. The A -demethylation of puromycin (XLlIl) [209, 210], its aminonucleoside (XLIV) [211], and a number of related compounds, including V-methyladenine and V,V-dimethyladenine, occurs in the liver microsomes of rodents [212]. In the guinea-pig the rate-limiting step in the metabolism of the aminonucleoside appears to be the demethylation of the monomethyl compound, which is the major urinary metabolite [213]. The relationship of lipid solubility to microsomal metabolism [214], and the induction of these demethylases in rats by pre-treatment with various drugs have been studied [215]. 

Although adenylic acid deaminase is a well-known enzyme that has been isolated in crystalline form, little work has been reported on its substrate specificity evidence for the deamination of 4-aminopyrazolo[3,4-d]pyrimidine ribonucleotide has been presented [118], but it is not known if it catabolizes any of the other intracellularly formed adenylic acid analogues. 

Several analogues of adenine or adenosine are reported to be incorporated into nucleic acids 2-fluoroadenosine [342], tubercidin [190, 192, 342a], toyacamycin [193,342a], sangivatnycin [342a, b], cordycepin [168,343,344], 4-aminopyrazolo[3, 4-d] pyrimidine [119], formycin [344a], and 9- -D-arabinofuranosyladenine [152, 154], The evidence for the incorporation of 9-(3-D-arabinofuranosyladenine has been questioned [345]. 

Aminopyrazolo[3,4-d]pyrimidines 257 were converted into the corresponding 4-aryl substituted derivatives 259 via treatment with alkyl nitrites and boiling in aromatic solvent. The isomer distribution of 259 prepared by these route was that predicted for a radical intermediate (ortho, meta, and para). The structure of isomers was established by H-NMR. Unusual fragmentation products were isolated these probably result from collapse of the radical intermediate 258 (83JOC4605). Methylation of 257 takes place at either N-1 or N-2. Further methylation affords methylamino derivatives structures of the products were established by C-NMR as well as by chemical methods (75JOC1822). 

Neutral 4-aminopyrazolo[3,4-d]pyrimidines exists in water in two tautomeric forms 1//-4-amino (1H4APP) and 2//-4-amino (2H4APP) isomers (X = 2H4APP/1H4APP = O.I at lOO C and OH tautomerization = 9.0kcal mol ). Interconversion of the two forms is catalyzed by and OH through either an intermediate cation common to both tautomers or through an intermediate anion. 

The use of formamide, which was introduced in 1956,117-119 is exemplified by the conversion of 3-amino-4-cyanopyrazole (97) to 4-aminopyrazolo-[3,4-d]pyrimidine (98) in good yield by boiling with formamide for 30 min.118 The product was conveniently obtained by diluting the cooled mass with water. Here, as in most other applications of the reaction, the temperature is not specified. This introduces uncertainty, because formamide vigorously expels bubbles of ammonia and carbon monoxide at about 200°-210°C, decomposing rather than boiling. An addition of acetic anhydride to improve yields has been suggested.120... 

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