4-aminoantipyrine is the most widely used analytical reagent for the estimation of phenol. It is used as a reagent for glucose determination in the presence of peroxidase and phenol. It is also used as indicator for trace phenol determinations in water. 4-aminoantipyrine (4-AAP) is defined as a compound that forms Schiff bases by condensing with various carbonyl compounds and is known for its ability to chelate metal ions, leading to applications in analytical chemistry and various fields including corrosion inhibition and antimicrobial activity. Phenolic compounds were determined by buffering the sample to a pH of 10.0 and adding 4-aminoantipyrine to produce a yellow or amber colored complex in the presence of ferricyanide ion. The colour is intensified through extraction of the complex into chloroform. Measurement of this colour quantitatively determines the phenol concentration of the sample.

Schiff Bases From 4-Aminoantipyrine

4-aminoantipyrine is a heterocyclic molecule with two nitrogen atoms in its ring joined by a carbonyl functional group and a highly reactive amine. The existence of heteroatoms affects the electron redistribution and gives an aromatic character, known as the heteroatom effect, which confers reactivity, chelating action, and other properties. As a result, it is used in a variety of research areas such as analytical, modern organic, bioorganic, and medicinal chemistry. 4-aminoantipyrine (4-aminophenazone) was first synthesized in the late nineteenth century by Friedrich Stolz and Ludwig Knorr and sold as Pyramidon, an antipyretic drug. It is a metabolite of aminopyrine and metamizole. The prodrug metamizole with analgesic, antipyretic, and anti-inflammatory effects was first used medically in Germany under the brand of Novalgin. Nonenzymatic breakdown of the metamizole results in 4-N-methylaminoantipyrine (4-MAA), which is then N-demethylated to 4-aminoantipyrine (4-AAP), which enters the systemic circulation. 4-AAP can form stable complexes with heme and has apparent denaturing effects on transportable proteins in the circulatory system. 4-AAP is an aromatic compound with analgesic, anti-inflammatory, and antipyretic properties. However, because of the risk of agranulocytosis, 4-AAP is rarely used as an analgesic nowadays.[1]

Regarding biochemical reactions and environmental monitoring, 4-AAP is the most commonly used for the colorimetric determination of phenolic compounds in wastewater, pesticides, and fungicides in the presence of alkaline oxidizing agents. Furthermore, it is used as a reagent in a wide variety of analytical applications, such as glucose determination in the presence of phenol as well as peroxidase and uric acid determination using hydrogen peroxide. Schiff bases obtained by the condensation of 4-aminoantipyrine and substituted salicylaldehydes (5-fluorosalicylaldehyde, 3-chloro-5-fluorosalicylaldehyde, 5-fluoro-3-methylsalicylaldehyde) and ferrocenecarboxaldehyde were first synthesized for this research. Therefore, after the characterization of Schiff bases derived from 4-aminoantipyrine, findings on antimicrobial activity, DNA cleavage, and glucose biosensor design are given in detail. Novel 4-aminoantipyrine-derived Schiff bases ((4AA-Fc), (4AA-SA), (4AA-FSA), (4AA-ClFSA), and (4AA-FMeSA)) were synthesized, characterized, and investigated for their antimicrobial and anticancer activities, in silico prediction of ADME and cytotoxicity properties, and glucose biosensing application. All novel Schiff bases had good antibacterial and antifungal activities. The difference in the MIC values of all compounds against the Gram-negative bacterial and fungal strains was statistically significant. Moreover, all compounds exhibited self-activating DNA cleavage ability at low concentrations without any external agents.

Synthesis and Biological Evaluation of 4-Aminoantipyrine Analogues

The aim of the present study is to carry out a simple synthesis of aminoantipyrine analogues and exploration of their antibacterial, cytotoxic, and anticonvulsant potential. The compounds were characterized employing multi-spectroscopic methods. The in vitro pharmacological response of a series of bacteria was screened employing serial dilution method. The derivatives were screened against maximal electro-shock for their anticonvulsant activity. Molecular docking was carried out to optimize the interaction of the compounds with HPV16-E7 receptors. Further, the in vitro cytotoxicity was tested against human cervical cancer (SiHa) cell lines.[2]

The compounds show protection against maximal electroshock, esp. 3-nirto- and 4- methyl-3-nitrobenzamido derivatives. In addition, they reveal appreciable DNA cleavage activities and interactions with HPV16-E7 protein receptors, esp. 3,5-dinitro- and 4-methyl-3-nitrobenzamido derivatives. Furthermore, they show potent activity against cervical cancer cells (LD50 value up to 1200 in the case of 4-methyl-3-nitrobenzamido derivative and an inhibition of a maximum of ~97% of cells).The simply synthesized aminoantipyrine derivatives show a variety of biological activities like antibacterial and anticancer effects. In addition, this is the first study demonstrating that 4-aminoantipyrine derivatives show an anticonvulsant activity.

A novel 4-aminoantipyrine-Pd(II) complex catalyzes Suzuki–Miyaura cross-coupling reactions

The sp2–sp2 carbon–carbon bond formation through cross-coupling reactions catalyzed by metal complexes has emerged as a powerful tool in organic synthesis. Transition metal complexes that have shown a wide range of biological activity are those containing the pyrazolone derivative 4-aminoantipyrine (4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one, or simply “4-AAP”). Despite the potential biological importance of 4-AAP, the catalytic activity of its transition metal complexes for C–C bond formation have not yet been investigated. Herein, we report the synthesis of the new 4-aminoantipyrine–Pd(II) complex [4-AAP–Pd(II)] by mixing Li2PdCl4, 4-aminoantipyrine in presence of NaOAc in MeOH at room temperature, and its performance as catalysts in SM cross-coupling reaction of structurally different aryl halides with phenylboronic acids. The biaryls are obtained in moderate to high yield.[3]

In summary, we have developed a mild, efficient and comparatively inexpensive methodology for the synthesis of biaryl compounds. This methodology uses our newly developed 4-aminoantipyrine–Pd(II) complex as a highly efficient precatalyst and general catalyst for the SM cross-coupling, works without the necessity of phosphine ligands, and was also found to be active for the cross-coupling of aryl iodides and bromides with substituted phenylboronic acids. The SM cross-coupling reaction can be carried out in EtOH, in the presence of air, with low catalyst loadings, and heating at reflux conditions for relatively short reaction times to afford biaryl compounds in good to excellent yields. The synthetic accessibility and stability under cross-coupling reaction conditions of 4-aminoantipyrine–Pd(II) complex make this complex a very promising precatalyst, and we will continue studying its applicability in various organic reactions.

References

[1]Erba? A, Dikim S, Arslan F, Bodur OC, Arslan S, ?zdemir F, Sar? N. Schiff Bases From 4-Aminoantipyrine: Investigation of Their In Silico, Antimicrobial, and Anticancer Effects and Their Use in Glucose Biosensor Design. Bioinorg Chem Appl. 2025 Apr 1;2025:2786064. doi: 10.1155/bca/2786064. PMID: 40201410; PMCID: PMC11978478.

[2]Ren, Houwei et al. “Synthesis and Biological Evaluation of 4-Aminoantipyrine Analogues.” Medicinal chemistry (Shariqah (United Arab Emirates)) vol. 18,1 (2022): 26-35. doi:10.2174/1573406416666201106105303

[3]Contreras-Celedón CA, Mendoza-Rayo D, Rincón-Medina JA, Chacón-García L. A novel 4-aminoantipyrine-Pd(II) complex catalyzes Suzuki-Miyaura cross-coupling reactions of aryl halides. Beilstein J Org Chem. 2014 Dec 1;10:2821-6. doi: 10.3762/bjoc.10.299. PMID: 25550748; PMCID: PMC4273307.