The logic behind this enduring popularity is structural. Purine is a fused pyrimidine–imidazole ring system whose shape and hydrogen-bonding pattern closely mimic the adenine portion of ATP, the universal energy currency of the cell. Because many disease-driving enzymes, particularly kinases, bind ATP in deep, well-defined pockets, purine-based molecules can slide into those sites and block them with remarkable efficiency. The review emphasizes that this ATP-like architecture is precisely why purine derivatives have become such productive kinase inhibitors, and why the scaffold appears in marketed drugs spanning immunosuppression, antiviral therapy, gout treatment, asthma, and leukemia, including azathioprine, acyclovir, allopurinol, theophylline, and clofarabine.

The most impressive potency numbers in the review come from anticancer work, where purine derivatives have been optimized against an expanding roster of molecular targets. A 2,9-disubstituted purine designed to inhibit the mutant EGFR variant L858R, a common driver of non-small-cell lung cancer, achieved an inhibitory concentration of just 1.9 nanomolar while suppressing receptor phosphorylation and reducing tumor growth in animal models. Other purine compounds have reached similarly low nanomolar potency against the PI3Kα signaling kinase, the mTOR regulator, the FLT3 kinase implicated in acute myeloid leukemia, and the Bcr-Abl fusion protein that defines chronic myeloid leukemia, with one trisubstituted derivative inhibiting Abl1 at 15 nanomolar and another blocking CDK9 at 11.3 nanomolar in leukemia cells.

Structure–activity relationship analysis across these anticancer series reveals consistent design rules. Modifications at the C-6 position of the purine ring are especially influential: arylamine or heteroaromatic substituents placed there create additional hydrophobic contacts within kinase binding pockets and reliably boost potency against CDK, EGFR, VEGFR, FLT3, and mTOR targets. Electron-withdrawing groups such as fluoro, chloro, and trifluoromethyl on attached aromatic rings strengthen binding through hydrophobic interactions, and halogenation is a recurring feature among the most active EGFR inhibitors. Substitutions at C-2, N-7, C-8, and N-9 fine-tune selectivity and cellular uptake, with piperazine rings and other cyclic amines at N-9 repeatedly shown to increase both kinase inhibition and cytotoxicity. Fused frameworks such as triazolopurines and pyrazolopyrimidines generally outperform simple purines because their added rigidity locks molecules into productive binding conformations.

Importantly, the review connects these small-molecule successes to fundamental cell biology. Blocking de novo purine biosynthesis at the enzyme GARFT starves cells of guanine nucleotides, which in turn limits the formation of GTP-bound Rheb, a small GTPase required to activate mTORC1 at the lysosomal membrane. Without that activation, protein synthesis stalls and cancer cell proliferation collapses. This pathway explains why purine metabolism itself, not merely purine-shaped inhibitors, has become a therapeutic target, and it aligns with separate findings that glioblastoma cells resist temozolomide by ramping up one-carbon-mediated purine synthesis, and that breast cancer metastasis depends on purine synthesis regardless of the local nutrient environment.

Beyond oncology, the review catalogs substantial progress against infectious diseases, exploiting a different structural vulnerability: many pathogens cannot make purines from scratch. The malaria parasite Plasmodium falciparum lacks a complete de novo pathway and must scavenge purines from host red blood cells through a salvage route funneled by the enzyme PfHGXPRT. Designers have attacked this dependency from several angles, and the most potent result is a 4-aminoquinoline–purine hybrid that reached 80 nanomolar activity against chloroquine-resistant parasites by combining heme detoxification disruption with purine metabolism interference. Acyclic nucleoside bisphosphonates targeting HGXPRT show moderate but highly selective activity, while nucleoside analogues with sugar-like fragments achieve better uptake through parasite transporters.

The antimicrobial sections document equally diverse mechanisms. Ethanol-bridged purine–azole hybrids inhibit methicillin-resistant Staphylococcus aureus at micromolar concentrations, apparently through membrane disruption and DNA interactions, while purine–benzimidazole hybrids beat norfloxacin against resistant strains. On the antifungal front, isothiazole–purine hybrids kill the rice pathogen Rhizoctonia solani by inhibiting pyruvate kinase, and a new class of purine analogues targeting fungal inositol polyphosphate kinases suppresses Cryptococcus neoformans by roughly 95 percent and synergizes with amphotericin B. N-9 substituted purines bearing morpholine rings match fluconazole against Candida albicans, with dihydrofolate reductase implicated as the target. In tuberculosis, the standouts include a purine derivative blocking the MbtA enzyme of mycobactin iron acquisition at 0.049 micromoles per liter and compounds inhibiting the cell-wall biosynthesis enzymes DprE1 and MurB, with amino acid conjugation and piperazine substitution emerging as recurring potency enhancers.

Antiviral applications extend the scaffold’s reach from human pathogens to crop protection. Chiral purine derivatives have shown activity against both acyclovir-sensitive and acyclovir-resistant herpes simplex virus type 1, with stereochemistry proving decisive, while purine-based phosphonates inhibit the adenylate cyclase toxin of Bordetella at 16 nanomolar. Against SARS-CoV-2, dimethylxanthine derivatives designed as dual inhibitors of the viral main protease and RNA-dependent RNA polymerase outperformed remdesivir in enzymatic assays, echoing the mechanism by which approved nucleoside analogues corrupt viral genome replication. Plant-virus studies, meanwhile, show purine–chalcone and sulfonamide nucleoside derivatives binding the tobacco mosaic virus coat protein and activating host defense responses, suggesting agricultural as well as pharmaceutical value.

Perhaps the most surprising breadth appears in the miscellaneous activity section, where purine chemistry touches nearly every organ system. Caffeine-based triazoles inhibit acetylcholinesterase at 0.49 micromolar, a dramatic improvement over the parent compound and a plausible route to Alzheimer’s therapeutics; purine-based DPP-4 inhibitors lower glucose in diabetic animal models; xanthine derivatives block adenosine receptors with submicromolar affinity for antifibrotic and cardiovascular indications; and 7-deazapurine nucleosides clear intracellular Trypanosoma cruzi and Leishmania infections in vivo with excellent selectivity. Mechanistic insights threaded through the review, such as the role of urate crystals and the P2X7 receptor in driving NLRP3 inflammasome activation during gout, and the ability of bacterial inosine to open OmpF channels and increase antibiotic uptake, illustrate how purine metabolism itself shapes disease outcomes in ways that new drugs could exploit.

The authors are careful to temper the enthusiasm. Most compounds surveyed remain preclinical, and the translation gap separating nanomolar enzyme inhibition from safe, orally available medicine involves pharmacokinetics, bioavailability, toxicity, and in vivo efficacy that many leads have not yet cleared. Still, the overall picture is one of a scaffold with unmatched versatility, in which deliberate substitution patterns, heterocycle fusion, electronic tuning, and linker engineering can be combined like adjustable dials to hit an extraordinary range of biological targets. As resistance to existing antimicrobials mounts and cancer increasingly exploits its own purine metabolism to survive treatment, the humble fused ring at the core of life’s information molecules looks less like a historical artifact of drug discovery and more like a platform whose most valuable derivatives may still be ahead.

Subject of Research: Structure–activity relationships and biological activities of purine and purine-derived compounds in medicinal chemistry and drug discovery

Article Title: Purine and its derivatives: Structure activity relationships, biological activities, and mechanistic insights

Article References: Gochhayat, S. J., Kavalapure, R. S., Vadivel, E., Shaikh, S. N., Kalakwade, A., Gharge, S., Ranade, S. D., Ramu, R., & Firdose, N. (2026). Purine and its derivatives: Structure activity relationships, biological activities, and mechanistic insights. Results in Chemistry, 31, Article 103896. https://doi.org/10.1016/j.rechem.2026.103896

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103896

Keywords: purine, medicinal chemistry, structure–activity relationship, kinase inhibitors, anticancer agents, antimalarial drugs, antimicrobial resistance, antiviral agents, antifungal agents, tuberculosis, purine metabolism, drug discovery

The Mannich reaction is deceptively simple. It condenses three components, typically an amine, formaldehyde or a related aldehyde, and a nucleophilic carbon center, into a single β-amino carbonyl product in one pot. Because the reaction tolerates an enormous range of substrates, it allows chemists to bolt aminomethyl groups onto almost any molecule bearing an acidic or nucleophilic carbon, instantly adding a basic, water-solubilizing handle that often improves binding to biological targets. Several FDA-approved heterocyclic drugs owe their existence to Mannich condensation, and the piperazine ring itself is prized for its conformational flexibility and its ability to engage in diverse interactions with proteins. Combining the two, the review’s authors contend, is a uniquely efficient way to generate the molecular diversity on which modern drug discovery depends.

The first major strategy surveyed is the classical three-component condensation. In one representative study, Janowska and colleagues reacted a substituted 1,2,4-triazole-3-thione with various piperazines and formaldehyde in ethanol at room temperature, obtaining antimicrobial Mannich bases in 32 to 62 percent yield within 24 hours, with products simply precipitating out of solution. Wujec and Typek used the same logic to prepare a single triazole-thione derivative in 81 percent yield in anhydrous ethanol. Perhaps most compelling for clinicians, several teams have grafted piperazine Mannich motifs onto existing fluoroquinolone antibiotics. Coupling ciprofloxacin or norfloxacin with piperazine derivatives and formaldehyde in dimethylformamide at room temperature delivered hybrid antibacterial compounds in yields of 71 to 83 percent, demonstrating that the reaction can upgrade established drugs rather than merely decorate novel cores.

The breadth of pharmacological classes reachable through this chemistry is remarkable. Avci and co-workers attached piperazine-containing Mannich arms to a naproxen scaffold, producing analgesic and anti-inflammatory candidates in 20 to 82 percent yield in boiling ethanol. Fan and colleagues condensed methylxanthines with piperazines under reflux to obtain fungicidal derivatives in 82 to 95 percent yield, among the highest reported in the review. Oxadiazole-thiones reacted with formaldehyde and substituted piperazines overnight at room temperature furnished anti-inflammatory and antimicrobial products spanning 29 to 89 percent yield, while coumarin and eupatilin derivatives made by the same logic showed anti-proliferative and antitumor activity against multiple human cancer cell lines. Even eugenol, the clove-derived phenol, was converted into a DPPH-scavenging antioxidant hybrid in 83 percent yield using N-methyl piperazine and excess formaldehyde in methanol.

The second strategy category involves multicomponent variations in which the Mannich step is performed last, after more complex frameworks have already been assembled. This late-stage aminomethylation is powerful because it lets chemists build elaborate molecular architecture first and then install the piperazine-containing pharmacophore with surgical precision. Rawat and colleagues, for example, first converted a triazole-5-thione with anisaldehyde into a Schiff base, then reacted that intermediate with piperazine and formaldehyde to reach the final antifungal product in 65 percent yield. Loganathan’s group pushed the concept further with a five-component sequence, condensing benzotriazole, para-nitrobenzaldehyde and piperazine into an intermediate that was subsequently coupled with amines and aldehyde to give antibacterial heterocycles in 83 to 87 percent yield against E. coli and Streptococcus.

Isatin, the indole-derived ketone that has become a favorite scaffold in anticancer research, features prominently in this section. Teams led by Raju, Verma and Mohamed all followed the same general blueprint: form an isatin Schiff base with an aromatic amine under acetic acid catalysis, then perform the Mannich condensation with formaldehyde and a piperazine derivative. The resulting hybrids, obtained in yields from 45 to 87 percent, showed anticancer and antibacterial activity, and the authors of the review walk through the detailed mechanistic proposal, in which protonated isatin undergoes nucleophilic attack, dehydration, and imine formation before the piperazine nitrogen delivers the final aminomethyl group. Nitrofuran-isatin hybrids made by a catalyst-free variant reached 80 to 85 percent yield with simple overnight stirring in ethanol.

The third and most forward-looking section catalogues catalytic and green approaches that address the classical reaction’s environmental shortcomings. Copper salts emerge as the stars of this show. Copper chloride enabled a one-pot synthesis of a maleopimaric acid derivative with striking antiviral activity against influenza A (H1N1), achieving an IC50 of 0.9 micromolar in just four hours at room temperature. Copper iodide promoted the coupling of N-propargylated triterpenic indoles with piperazines and formaldehyde at 60 degrees Celsius, yielding compounds active against SARS-CoV-2, and also drove the synthesis of oxadiazole kinase inhibitors and benzodioxole-piperazine hybrids at room temperature in dimethyl sulfoxide. Indium chloride catalyzed fluoroquinolone-triazole hybrids in yields up to 95 percent, while simple acetic acid and hydrochloric acid proved sufficient for indole-piperazine and benzimidazole systems.

Microwave assistance delivers perhaps the most dramatic efficiency gains. Albelwi and co-workers showed that triazole-based Mannich bases could be made in ethanol with significantly higher yields and drastically shorter reaction times under microwave irradiation compared with conventional heating, a result that matters for scale-up because microwave protocols cut both energy consumption and solvent load. The review also highlights catalyst-free protocols run in water-tolerant conditions, solvent-free setups, and recyclable catalytic systems, all of which align the chemistry with the principles of sustainable synthesis. The authors note that these greener methods do not merely reduce waste; they frequently improve regioselectivity, a persistent problem when asymmetric piperazines can react at either nitrogen to give isomeric mixtures that are difficult to purify.

The biological payoff of all this synthetic ingenuity is documented in detail. An oxadiazole-piperazine Mannich base bearing a benzyl substituent showed IC50 values as low as 6.49 micromolar against breast cancer cells, while a triazole-based MMP inhibitor reached 0.390 micromolar against colon adenocarcinoma and was flagged as drug-like by ADMET prediction. Structure-activity relationships repeatedly showed that bulky, basic piperazine substituents enhance potency, and that electron-withdrawing groups on aromatic rings boost antifungal activity. Against tuberculosis, an indole-based N-benzylated Mannich base achieved an MIC of 1.6 micrograms per milliliter against Mycobacterium tuberculosis H37Rv. The review closes with a look ahead: the authors anticipate solvent-free methodologies, C-H activation to widen substrate scope, biocatalytic variants, and integration with photoredox and flow chemistry platforms. If those predictions hold, the Mannich reaction, now more than a century old, may spend its next hundred years at the center of drug discovery’s most productive chemistry.

Subject of Research: Mannich-type multicomponent synthesis of functionalized piperazine-based bioactive scaffolds

Article Title: Multicomponent mannich-type approaches to the synthesis of functionalized piperazine-based bioactive scaffolds

Article References: Mubashra, S., Ahmad, M., Aslam, S., Al-Hussain, S. A., & A. Zaki, M. E. (2026). Multicomponent mannich-type approaches to the synthesis of functionalized piperazine-based bioactive scaffolds. Journal of Saudi Chemical Society, 30(3), Article 43. https://doi.org/10.1007/s44442-026-00095-5

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00095-5

Keywords: piperazine, Mannich reaction, multicomponent reactions, medicinal chemistry, green chemistry, anticancer agents, antiviral agents, antibacterial agents, heterocyclic compounds, copper catalysis, microwave-assisted synthesis, drug discovery