Formycin A

The molecule 7-aminopyrazolopyrimidine is related to the DNA base adenine. It is the base attached to ribose in formycin A, which is believed to have potential therapeutic value. It is also shown in Figure 5. There is a paradox in this system. This molecule is deactivated by the enzyme adenosine deaminase (ADA). In solution the N7H tautomer predominates. This structure however inhibits ADA, and this tautomer of formycin A would not be deactivated by the enzyme. 

X-Ray data for ALP 61, formycine A 62, as well as the pyrazolopyrimidine derivatives 63 and oxazinopyrimidine 64 have been discussed in CHEC-II. 

An accurate HPLC method for the determination of formycin A (FA) in plasma utilizing a Liichromsorb RP-18 column has been described and successfully applied <1999JCH383>. 

Steady-state and time-resolved emission spectroscopy was used to study the interaction of E. colt PNP with its specific inhibitors formycin B, FA, and A -l-methylformycin A. Complexation was found to induce tautomeric shifts <2000BBA1467>. Carbocyclic analogues of formycin A and B have been recently synthesized <2004T8233>. The synthesis utilized 417 as starting material which was converted into 418 via a multistage synthesis. The latter could be converted into the formycin analogue (Scheme 36) <2004TL8233>. 

A quantum chemical study of formycin A (54a) and its 2-amino (54b) and 2-fluoro (54c) derivatives was performed using the semiempirical MNDO and AMI methods as well as an ah initio STO-3G... 

The dynamic tautomerism of formycin A (54a) was investigated by a temperature jump method and the mechanism of tautomerism discussed (78JA3957). 

Formycin A was initially isolated from rice mold <65JAN259> and identified <66JHC110, 66TL597) as 3-ribofuranosylpyrazolo[4,3-G ]pyrimidine-7-amine (54a). The reported synthesis utilizes the pyra-zole derivative (522) as starting material which is converted in situ on treatment with zinc dust in methanol in the presence of ammonium chloride into the amine (523) which is then reacted with formamidine to yield formycin A after deprotection (Scheme 53) <78CCC1431>. 

A synthesis of formycin A employs the 1,4-dinitropyrazole (524) which is converted into the nitrile (525) on treatment with cyanide ion (Equation (72)). The latter is then reduced and treated with formamide or formamidine to give formycin A (54a) <80CJC2624,8lJCS(Pl)2374, 91JCS(P1)1077>. 

Formycin B (528) is prepared from the pyrazole (529) by treatment similar to that reported for the synthesis of formycin A (54a) from (523) (72CCC2786). 

Alternatively, the same reaction can be assayed if adenosine is replaced by formycin A (FoA) (Fig. 4.14), a fluorescent analog. With this substrate, one product of the adenosine kinase reaction would be FoMP, the fluorescent analog of AMP, while AMP formed directly from ATP would not be fluorescent. Therefore, by monitoring both the fluorescence and the ultraviolet absorbance, using equipment arranged as shown in Figure 4.15, the analyst could follow both the kinase reaction and any secondary reactions. 

Figure 4.14 Comparison of structures of adenosine and its fluorescent analog formycin A.

The reaction mixture contained the substrate and buffer, and the reaction was started by the addition of the enzyme. In one study, the substrate was j formycin 5 -monophosphate, a fluorescent analog of AMP. The formation of i formycin A, the analog of adenosine, is shown in Figure 9.90 as a function of j incubation time. 

Adenosine kinase catalyzes the transfer of phosphate from ATP to adenosine (Ado) to form AMP and ADP. The separation of the reactants, Ado and ATP, from the products, AMP and ADP, can be accomplished by reversed-phase HPLC (Ci8) with isocratic elution with a mobile phase of 0.1 M potassium phosphate (pH 5.5) and 10% methanol. Detection depends on the substrate. In this assay, it is useful to replace the substrate adenosine with the fluorescent analog formycin A (FoA) and to monitor the column eluent with a fluorescence detector. Thus, ATP and any of its hydrolytic products will not be detected. 

The reaction mixture contained cyclic formycin monophosphate, an analog of cAMP, as the substrate, Tris-HCl (pH 7.5) as buffer, and MgQ2. The reaction was started by the addition of the enzyme. Samples were removed at intervals and injected directly onto the reversed-phase column for analysis. Figure 9.108 shows chromatograms after 10 and 30 minutes of incubation. While the amount of cFoMP substrate in the incubation mixture has declined and the amount of product FoMP has increased, the amount of formycin A (FoA), the analog of adenosine, has remained unchanged. When the area of each peak is plotted as a function of reaction time, the data shown in the central inset are obtained. Although these data clearly illustrate the activity of the cyclic phosphodiesterase, they also show the absence of any 5 -nucleotidase. 

Asn243 side-chain in a manner that converted it from a donor of a hydrogen bond to the N of guanine to an acceptor of a hydrogen bond from the inhibitor In our studies, 9-deaza AMP (formycin A monophosphate)... 

Figure 17-7. Structures of adenosine and related nucleosides which serve as substrates for S-adenosyl-L-homocysteine hydrolase. 1, Adenosine 2, formycin A 3, neburalin 4, adenosine Af-oxide 5, 2-chloroadenosine 6, tubercidine 7, N6-methyladenosine 8, inosine 9, 1-methyladenosine.

Compounds structurally related to adenosine 5 -triphosphate also exhibit inhibition. Among adenosine 5 -pyrophosphate, adenosine 5 -phos-phate, adenosine, and adenine, adenosine showed the strongest inhibition. This result indicated that the adenine and n-ribose moieties of adenosine 5 -triphosphate bind with the enzyme. Formycin A is an analog of adenosine, and exhibits inhibition (61% at 3.2 mM) formycin B is less active. This suggested that the amino group of adenosine binds with the... 

Formycin A (LXXIV, R = NH2) and B, (LXXIV, R = OH), and pyra-zomycin (LXXV) are natural products having weak antiviral activity. The first two are active against influenza in vitro [277] and the last has activity against vaccinia in mice [278]. -They are unique in being nucleoside analogues with the rare C-riboside link. 

Formamido-3,6-dideoxy-D-galactose, A-376 2"-iV-Formimidoylistamycin A, 1-82 2"-Formimidoylsporaricin A, S-67 Formycin A, F-20... 

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