CuI-Catalyzed Selenylation of Pyrrolo[2,1-a]isoquinolines and Other Electron-Rich Heteroarenes

We have established a mild CuI-catalyzed selenylation of pyrrolo[2,1-a]isoquinoline derivatives in the presence of mCPBA (m-chloroperoxybenzoic acid) at ambient temperature. Corresponding organoselenides have been prepared readily in 53-92% yields. This process can also be expanded to the modification of pyrroles, azaindole, and indoles, delivering the desired heterocyclic selenides in moderate to good yields.

Domino Approach to Heterocycles-Based Unsymmetrical Triarylmethanes through Heteroannulation of 2-(2-Enynyl)-pyridines with Enaminones

Herein, we report a copper-catalyzed protocol to access unsymmetrical triarylmethanes containing both indolizine and the chromone scaffolds in the same molecule via a 5-endo-dig cyclization of 2-(2-enynyl)-pyridines followed by reaction with 2-hydroxyaryl enaminones. A variety of 2-hydroxyaryl enaminones and 2-(2-enynyl)-pyridines were subjected to reaction under the optimal reaction conditions, and the respective triarylmethanes were obtained in good to excellent yields.

Bioactive atropisomers: Unraveling design strategies and synthetic routes for drug discovery

Atropisomerism, an expression of axial chirality caused by limited bond rotation, is a prominent aspect within the field of medicinal chemistry. It has been shown that atropisomers of a wide range of compounds, including established FDA-approved drugs and experimental molecules, display markedly different biological activities. The time-dependent reversal of chirality in atropisomers poses complexity and obstacles in the process of drug discovery and development. Nonetheless, recent progress in understanding atropisomerism and enhanced characterization methods have greatly assisted medicinal chemists in the effective development of atropisomeric drug molecules. This article provides a comprehensive review of their special design thoughts, synthetic routes, and biological activities, serving as a reference for the synthesis and biological evaluation of bioactive atropisomers in the future.

An Overview on the Synthesis of Lamellarins and Related Compounds with Biological Interest

Lamellarins are natural products with a [3,4]-fused pyrrolocoumarin skeleton possessing interesting biological properties. More than 70 members have been isolated from diverse marine organisms, such as sponges, ascidians, mollusks, and tunicates. There is a continuous interest in the synthesis of these compounds. In this review, the synthetic strategies for the synthesis of the title compounds are presented along with their biological properties. Three routes are followed for the synthesis of lamellarins. Initially, pyrrole derivatives are the starting or intermediate compounds, and then they are fused to isoquinoline or a coumarin moiety. Second, isoquinoline is the starting compound fused to an indole moiety. In the last route, coumarins are the starting compounds, which are fused to a pyrrole moiety and an isoquinoline scaffold. The synthesis of isolamellarins, azacoumestans, isoazacoumestans, and analogues is also described. The above synthesis is achieved via metal-catalyzed cross-coupling, [3 + 2] cycloaddition, substitution, and lactonization reactions. The title compounds exhibit cytotoxic, multidrug resistance (MDR), topoisomerase I-targeted antitumor, anti-HIV, antiproliferative, anti-neurodegenerative disease, and anti-inflammatory activities.

Base-Mediated Cascade Lactonization/1,3-Dipolar Cycloaddition Pathway for the One-Pot Assembly of Coumarin-Functionalized Pyrrolo[2,1-a]isoquinolines

An elegant and highly concise strategy for the construction of coumarin-functionalized pyrrolo[2,1-a]isoquinolines from available propargylamines and isoquinolinium N-ylides has been disclosed. In this reaction, isoquinolinium N-ylides acted as a C2 synthon to form a coumarin ring as well as a 1,3-dipole to construct a pyrrole ring in a single pot. This cascade process involves 1,4-conjugate addition/lactonization/1,3-dipolar cycloaddition to construct four chemical bonds (one C-O bond and three C-C bonds) and two new heterocyclic skeletons. Additionally, most of these compounds showed good fluorescence properties and exhibited high molar extinction coefficient and large Stokes shifts.

An Overview of the Synthesis of 3,4-Fused Pyrrolocoumarins of Biological Interest

3,4-Fused pyrrolocoumarins, synthetically prepared or naturally occurring, possess interesting biological properties. In this review, the synthetic strategies for the synthesis of the title compounds are presented along with their biological activities. Two routes are followed for that synthesis. In one, the pyrrole ring is formed from coumarin derivatives, such as aminocoumarins or other coumarins. In the other approach, the pyranone moiety is built from an existing pyrrole derivative or through the simultaneous formation of coumarin and pyrrole frameworks. The above syntheses are achieved via 1,3-dipolar cycloaddition reactions, Michael reaction, aza-Claisen rearrangement reactions, multi-component reactions (MCR), as well as metal-catalyzed reactions. Pyrrolocoumarins present cytotoxic, antifungal, antibacterial, α-glucosidase inhibition, antioxidant, lipoxygenase (LOX) inhibition, and fluorescent activities, as well as benzodiazepine receptor ability.

Design, synthesis, and biological evaluation of novel benzo[6,7]indolo[3,4-c]isoquinolines as anticancer agents with topoisomerase I inhibition

A novel series of benzo[6,7]indolo[3,4-c]isoquinolines 3a-3f was designed by scaffold hopping of topoisomerase I inhibitor benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs), which were developed by structural modification of the natural marine product lamellarin. The unconventional pentacycle was constructed by Bischler-Napieralski-type condensation of amide 11 and subsequent intramolecular Heck reaction. In vitro anticancer activity of the synthesized benzo[6,7]indolo[3,4-c]isoquinolines was evaluated on a panel of 39 human cancer cell lines (JFCR39). Among the compounds tested, N-(3-morpholinopropyl) derivative 3e showed the most potent antiproliferative activity, with a mean GI50 value of 39 nM. This compound inhibited topoisomerase I activity by stabilizing the enzyme-DNA complex.

TBHP/Et3N-Promoted Chemoselective Formylation and Peroxidation of Pyrrolo[2,1-a]isoquinolines

An efficient formylation of pyrrolo[2,1-a]isoquinoline derivatives has been reached by the use of TBHP (tBuOOH) and Et3N as the mediator. In this strategy, CHO and CDO can be readily incorporated into heteroarenes by the utilization of CHCl3 and CDCl3 as the carbonyl sources. Interestingly, a solvent-controlled chemoselectivity was observed. The use of PhCl as a solvent resulted in dearomatization and peroxidation of pyrrolo[2,1-a]isoquinolines, delivering functionalized peroxides in 53-64% yields.

Nature-Inspired 1-Phenylpyrrolo[2,1-a]isoquinoline Scaffold for Novel Antiproliferative Agents Circumventing P-Glycoprotein-Dependent Multidrug Resistance

Previous studies have shown that some lamellarin-resembling annelated azaheterocyclic carbaldehydes and related imino adducts, sharing the 1-phenyl-5,6-dihydropyrrolo[2,1-a]isoquinoline (1-Ph-DHPIQ) scaffold, are cytotoxic in some tumor cells and may reverse multidrug resistance (MDR) mediated by P-glycoprotein (P-gp). Herein, several novel substituted 1-Ph-DHPIQ derivatives were synthesized which carry carboxylate groups (COOH, COOEt), nitrile (CN) and Mannich bases (namely, morpholinomethyl derivatives) in the C2 position, as replacements of the already reported aldehyde group. They were evaluated for antiproliferative activity in four tumor cell lines (RD, HCT116, HeLa, A549) and for the ability of selectively inhibiting P-gp-mediated MDR. Lipophilicity descriptors and molecular docking calculations helped us in rationalizing the structure-activity relationships in the P-gp inhibition potency of the investigated 1-Ph-DHPIQs. As a main outcome, a morpholinomethyl Mannich base (8c) was disclosed which proved to be cytotoxic to all the tested tumor cell lines in the low micromolar range (IC50 < 20 μM) and to inhibit in vitro the efflux pumps P-gp and MRP1 responsible for MDR, with IC50s of 0.45 and 12.1 μM, respectively.

Iron-Catalyzed Synthesis of Peroxylpyrrolo[2,1-a]isoquinolines through Oxidative Dearomatization

A mild late-stage modification of pyrrolo[2,1-a]isoquinolines was established through iron-catalyzed oxidative dearomatization and peroxidation. Peroxylated pyrroloisoquinolines have been prepared readily with hydroperoxide in low to good yields (up to 72%) at room temperature. Interestingly, the treatment of fully aromatized pyrrolo[1,2-a]quinolines under the current reaction system resulted in the formation of ring-opening products.

NH4OAc/DMSO-Promoted Benzylation of Pyrrolo[2,1-a]isoquinolines

Benzylation of pyrrolo[2,1-a]isoquinoline derivatives has been realized with various phenols by the use of ammonium acetate as a promoter (20 examples, up to 84% yield). DMSO served as the source of methylene and solvent. The employment of iron chloride as a catalyst can also afford the desired benzylated products in moderate to good yields (11 examples, up to a 74% yield).

AcBr/DMSO Mediated Sulfenylation of Pyrrolo[2,1-a]isoquinolines

We have developed a mild sulfenylation of pyrrolo[2,1-a]isoquinolines with acetyl bromide and dimethyl sulfoxide. A wide range of functionalized pyrrolo[2,1-a]isoquinolines could be prepared efficiently through the formation of a C-S bond with thiophenols (27 examples, 36-94% yields). The current strategy can also be utilized for functionalization of pyrrolo[1,2-a]quinolines and indole.

Nitration of Pyrrolo[2,1-a]isoquinolines

We have successfully modified a series of pyrrolo[2,1-a]isoquinolines via direct nitration under mild reaction conditions. Easily accessible nitrates including CAN, Cu(NO₃)₂·H₂O, and Fe(NO₃)₃·9H₂O all can serve as effective nitrating reagents for functionalizing pyrrolo[2,1-a]isoquinolines. Various nitro-bearing pyrrolo[2,1-a]isoquinolines have been efficiently prepared in acceptable to good yields.

Synthesis of Pyrrolo[2,1-a]isoquinolines through Cu-Catalyzed Condensation/Addition/Oxidation/Cyclization Cascade

We have developed a copper-catalyzed synthesis of pyrrolo[2,1-a]isoquinolines with terminal alkynes, aldehydes, and tetrahydroisoquinolines. A variety of pyrrolo[2,1-a]isoquinolines have been prepared in 17-69% yield via a condensation/Mannich-type addition/oxidation/cyclization cascade sequence. Modifications through simple chemical transformations provided highly functionalized molecules containing a privileged framework.

Acid-Promoted Redox-Annulation toward 1,2-Disubstituted-5,6-dihydropyrrolo[2,1-α]isoquinolines: Synthesis of the Lamellarin Core

An efficient synthesis of a variety of 1,2-disubstituted-5,6-dihydropyrrolo[2,1-α]isoquinoline derivatives via an acid-promoted cyclization reaction between 1,2,3,4-tetrahydroisoquinoline (THIQ) and substituted α,β-unsaturated aldehyde derivatives is reported. This cycloaddition allows access to structurally diverse multisubstituted dihydropyrrolo[2,1-α]isoquinolines in moderate to good yields, which was the core scaffold of marine natural alkaloid lamellarins.

CK2 and protein kinases of the CK1 superfamily as targets for neurodegenerative disorders

Casein kinases are involved in a variety of signaling pathways, and also in inflammation, cancer, and neurological diseases. Therefore, they are regarded as potential therapeutic targets for drug design. Recent studies have highlighted the importance of the casein kinase 1 superfamily as well as protein kinase CK2 in the development of several neurodegenerative pathologies, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. CK1 kinases and their closely related tau tubulin kinases as well as CK2 are found to be overexpressed in the mammalian brain. Numerous substrates have been detected which play crucial roles in neuronal and synaptic network functions and activities. The development of new substances for the treatment of these pathologies is in high demand. The impact of these kinases in the progress of neurodegenerative disorders, their bona fide substrates, and numerous natural and synthetic compounds which are able to inhibit CK1, TTBK, and CK2 are discussed in this review.

Modification of Pyrrolo[2,1-a]isoquinolines and Polysubstituted Pyrroles via Methylenation with Acetyl Chloride and Dimethylsulfoxide

A convenient synthesis of methylene-bridged pyrrolo[2,1-a]isoquinolines has been developed. Treatment of pyrroloisoquinolines with acetyl chloride and dimethylsulfoxide (DMSO) at ambient temperature afforded bispyrroloisoquinolylmethanes in 17-85% yields. This reaction system can also be expanded to the synthesis of bispyrrolylmethanes (34-94% yields). Easy chemical transformation of methylene-bridged pyrroloisoquinoline provided an unsymmetric acid and amide possessing a privileged framework.

Transition-Metal-Free Alkylative Aromatization of Tetralone Using Alcohol/Amino Alcohol towards the Synthesis of Bioactive Naphthol and Benzo[e/g]indole Derivatives

Herein, we report alkylative aromatization of tetralone for the synthesis of bioactive naphthols and benzo[e/g]indole derivatives using alcohols in the presence of NaOH via an aerobic oxidative cross-coupling protocol. This is a general and transition-metal-free method, which uses an inexpensive base, avoids inert conditions, and furnishes water and hydrogen peroxide as the byproducts. Moreover, this method demonstrated with wide substrate scope and obtained exclusive regioselectivity.

Efficient synthesis of pentasubstituted pyrroles via intramolecular C-arylation

Immobilized L-aspartic acid beta-methyl ester (Fmoc-Asp(OMe)-OH) was reacted with 4-nitrobenzenesulfonyl chloride, followed by alkylation with various α-haloketones. The resulting intermediates were treated with potassium trimethylsilanolate, which yielded tetrasubstituted pyrroles after a one-step transformation consisting of sequential C-arylation, aldol condensation and spontaneous aromatization. The discovered synthetic strategy enables fast and simple access to pentasubstituted and functionalized pyrroles from a number of readily available starting materials.

A Two-Step Approach to a Hexacyclic Lamellarin Core via 1,3-Dipolar Cycloaddition of Isoquinolinium Ylides to Nitrostilbenes

The 1,3-dipolar cycloaddition reaction of isoquinolinium ylides to nitrostilbenes provides an approach to 1,2-diarylpyrrolo[2,1-a]isoquinolinium-3-carboxylates and then to a complete hexacyclic lamellarin core.

I2-DMSO-Mediated N-H/α-C(sp3)-H Difunctionalization of Tetrahydroisoquinoline: Formal [2 + 2 + 1] Annulation for the Construction of Pyrrolo[2,1-a]isoquinoline Derivatives

An I₂-DMSO-mediated cascade reaction using methyl ketones and 1,2,3,4-tetrahydroisoquinolines (THIQs) as commercially available substrates has been developed for the construction of pyrrolo[2,1-a]isoquinoline derivatives. This metal-free process involves N-H/α-C(sp³)-H difunctionalization of THIQ. Two C-C bonds and one C-N bond are formed in one pot under mild conditions. Besides, a quaternary carbon center has been constructed in this transformation efficiently.

Recent progress in the synthesis of pyrrolo[2,1-a]isoquinolines

Pyrrolo[2,1-a]isoquinolines occur frequently in a large number of bioactive natural products and pharmaceutically important molecules. The synthesis of pyrrolo[2,1-a]isoquinoline derivatives is an easy and useful way to produce artificial molecules with potential applications. A huge number of excellent methodologies for constructing pyrrolo[2,1-a]isoquinolines have been reported in the last decade. This review summarizes the recent advances in this research field covering from 2011 to 2021.

Design, synthesis via a one-pot approach and molecular docking studies of novel pyrrolo[2,1-a]isoquinoline derivatives

This new investigation describes an efficient three-component approach for the stereoselective synthesis of pyrrolo[2,1-a]isoquinolines from readily available isatins, chalcones and 1,2,3,4-tetrahydroisoquinoline without using any metal catalyst or additive.

An Expeditious Modular Hybrid Strategy for the Diversity-Oriented Synthesis of Lamellarins/Azalamellarins with Anticancer Cytotoxicity

A modular hybrid strategy has been developed for the diversity-oriented synthesis of lamellarins/azalamellarins. The common pentacyclic pyrrolodihydroisoquinoline lactone/lactam core was formed via the Michael addition/ring closure (Mi-RC) and the copper(I) thiophene-2-carboxylate (CuTC)-catalyzed C-O/C-N Ullmann coupling. Subsequent direct functionalization at C1, DDQ-mediated C5═C6 oxidation, and global deprotection of all benzyl-type O- and N-protecting groups furnished the desired lamellarins/azalamellarins. The late-stage functionalization at C1 provided a handle to accommodate a wider scope of functional groups as they need to tolerate only the DDQ oxidation and global deprotection. Moreover, with the C1-H pyrrole as the late-stage common intermediate, it was also possible to divergently exploit not only its nucleophilic nature to react with some electrophilic species but also some transition-metal-catalyzed cross-coupling reactions (via the intermediacy of the C1-iodopyrrole) to incorporate diversity at this position. Overall, this strategy simplifies the preparation of lamellarins/azalamellarins; including the Mi-RC, these C1-structurally diverse analogues could be prepared efficiently in 6-7 steps from the easily accessed 1-acetoxymethyldihydroisoquinoline and β-nitrocinnamate. Some selected azalamellarins were evaluated for their inhibitory effect against HeLa cervical cancer cells. An acute induction of intrinsic apoptosis was detected and may lead to growth suppression of or cytotoxicity against cancer cells.

Synthesis and Toxicity Evaluation of New Pyrroles Obtained by the Reaction of Activated Alkynes with 1-Methyl-3-(cyanomethyl)benzimidazolium Bromide

A series of new pyrrole derivatives were designed as chemical analogs of the 1,4-dihydropyridines drugs in order to develop future new calcium channel blockers. The new tri- and tetra-substituted N-arylpyrroles were synthesized by the one-pot reaction of 1-methyl-3-cyanomethyl benzimidazolium bromide with substituted alkynes having at least one electron-withdrawing substituent, in 1,2-epoxybutane, acting both as the solvent and reagent to generate the corresponding benzimidazolium N3-ylide. The structural characterization of the new substituted pyrroles was based on IR, NMR spectroscopy as well as on single crystal X-ray analysis. The toxicity of the new compounds was assessed on the plant cell using Triticum aestivum L. species and on the animal cell using Artemia franciscana Kellogg and Daphnia magna Straus crustaceans. The compounds showed minimal phytotoxicity on Triticum rootlets and virtually no acute toxicity on Artemia nauplii, while on Daphnia magna, it induced moderate to high toxicity, similar to nifedipine. Our research indicates that the newly synthetized pyrrole derivatives are promising molecules with biological activity and low acute toxicity.

Total Synthesis of Lamellarins G, J, L, and Z Using One-Pot Halogen Dance/Negishi Coupling

A bottom-up synthesis of lamellarins G, J, L, and Z was achieved via one-pot halogen dance/Negishi coupling of a lithiated dibromopyrrole derivative. The easily accessible dibromopyrrole bearing an ester moiety underwent halogen dance smoothly at -78 °C within 10 min. The resultant α-pyrrolyllithium was transmetalated to the corresponding organozinc species, which was then coupled with an aryl iodide in the presence of catalytic palladium to provide the fully substituted pyrrole. Subsequent halogen-lithium exchange was performed to incorporate a boronate group exclusively at the β position proximal to the ester moiety. This synthetic intermediate allowed stepwise diarylation for the total synthesis of lamellarins G, J, L, and Z.

Microwave-Assisted Palladium-Catalyzed Reductive Cyclization/Ring-Opening/Aromatization Cascade of Oxazolidines to Isoquinolines

An efficient palladium-catalyzed reaction of N-propargyl oxazolidines for the construction of 4-substituted isoquinolines under microwave irradiation is developed. This transformation proceeds through a sequential palladium-catalyzed reductive cyclization/ring-opening/aromatization cascade via C-O and C-N bond cleavages of the oxazolidine ring. The practical value of this method has also been explored by conducting a millimole-scale reaction, as well as by transforming the isoquinoline into a key intermediate for the synthesis of a lamellarin analogue.

Efficient synthesis of novel indolizine C-nucleoside analogues via coupling of sugar alkynes, pyridines and α-bromo carbonyl compounds in one pot

The synthesis of novel indolizine C-nucleoside analogues has been achieved by the three-component coupling reaction of sugar alkynes, pyridines and α-bromo carbonyl compounds in one pot. The corresponding products are obtained in good to excellent yields. 49 examples have been given. The synthetic method is convenient, practical and efficient. It is suitable for various substrates including structurally diversified sugar alkynes with sensitive groups. The sugar alkynes include pyranosides, furanosides, and acyclic sugars. A plausible mechanism for the formation of indolizine C-nucleoside analogues has been elucidated.

Cascade synthesis of 2,4-disulfonylpyrroles by the sulfonylation/[2 + 3]-cycloaddition reactions of gem-dibromoalkenes with arylsulfonyl methyl isocyanides

An efficient cascade reaction involving sulfonylation and [2 + 3]-cycloaddition reactions of gem-dibromoalkenes with arylsulfonyl methyl isocyanides was described for the synthesis of 3-aryl-2,4-disulfonyl-1H-pyrroles. The main highlight of this study is the introduction of a new dual-functional reactivity of arylsulfonyl methyl isocyanides as the sulfonyl source as well as a 1,3-dipolar reagent in the same reaction. This system is facilitated by Cs2CO3 mediation in DMSO and 100 °C conditions.

Lamellarin 14, a derivative of marine alkaloids, inhibits the T790M/C797S mutant epidermal growth factor receptor

The emergence of acquired resistance is a major concern associated with molecularly targeted kinase inhibitors. The C797S mutation in the epidermal growth factor receptor (EGFR) confers resistance to osimertinib, a third‐generation EGFR‐tyrosine kinase inhibitor (EGFR‐TKI). We report that the derivatization of the marine alkaloid topoisomerase inhibitor lamellarin N provides a structurally new class of EGFR‐TKIs. One of these, lamellarin 14, is effective against the C797S mutant EGFR. Bioinformatic analyses revealed that the derivatization transformed the topoisomerase inhibitor‐like biological activity of lamellarin N into kinase inhibitor‐like activity. Ba/F3 and PC‐9 cells expressing the EGFR in‐frame deletion within exon 19 (del ex19)/T790M/C797S triple‐mutant were sensitive to lamellarin 14 in a dose range similar to the effective dose for cells expressing EGFR del ex19 or del ex19/T790M. Lamellarin 14 decreased the autophosphorylation of EGFR and the downstream signaling in the triple‐mutant EGFR PC‐9 cells. Furthermore, intraperitoneal administration of 10 mg/kg lamellarin 14 for 17 days suppressed tumor growth of the triple‐mutant EGFR PC‐9 cells in a mouse xenograft model using BALB/c nu/nu mice. Thus, lamellarin 14 serves as a novel structural backbone for an EGFR‐TKI that prevents the development of cross‐resistance against known drugs in this class.

[3 + 2]-Annulation of gem-Difluoroalkenes and Pyridinium Ylides: Access to Functionalized 2-Fluoroindolizines

A [3 + 2]-annulation of gem-difluoroalkenes and pyridinium ylides was developed employing ambient air as the sole oxidant in an open-vessel manner, affording a series of multifunctionalized 2-fluoroindolizines in moderate to good yields. In this reaction, gem-difluoroalkene acts as a C2 synthon and entirely avoids the competitive addition-elimination process, which provides facile access to 2-fluoroindolizines.

Concise synthesis and in vitro anticancer activity of benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs), topoisomerase I inhibitors based on the marine alkaloid lamellarin

Benzo[g][1]benzopyrano[4,3-b]indol-6(13H)-ones (BBPIs) are potent anticancer compounds having unique BBPIs ring system designed on the basis of the marine natural product lamellarin D. In this study, we describe an alternative synthesis of a 2-demethoxy series of BBPIs, employing van Leusen pyrrole synthesis and an intramolecular Heck reaction as the key reactions. Cytotoxicity of the derivatives against several cancer and normal cell lines is reported.

Diverse synthesis of pyrrolo/indolo[3,2-c]coumarins as isolamellarin-A scaffolds: a brief update

This review presents a different synthetic approach of pyrrolo/indolo[3,2-c]coumarins via classical reactions including metal-catalyzed and green reaction protocols.

Recent progress in the total synthesis of pyrrole-containing natural products (2011–2020)

This review discusses total syntheses of pyrrole-containing natural products over the last ten years, highlighting recent advances in the chemistry of pyrroles in the context of their innate reactivity, and their preparation in complex settings.

A review: Biologically active 3,4-heterocycle-fused coumarins

The combination of heterocycles offers a new opportunity to create novel multicyclic compounds having improved biological activity. Coumarins are ubiquitous natural heterocycle widely adopted in the design of various biologically active compounds. Fusing different heterocycles with coumarin ring is one of the interesting approaches to generating novel hybrid molecules having highlighted biological activities. In the efforts to develop heterocyclic-fused coumarins, a wide range of 3,4-heterocycle-fused coumarins have been introduced bearing outstanding biological activity. The effect of heterocycles annulation at 3,4-positions of coumarin ring on the biological activity of the target structures were discussed. This review focuses on the important progress of 3,4-heterocycle-fused coumarins providing better insight for medicinal chemists on the design and preparation of biologically active heterocycle-fused coumarins with a significant therapeutic effect in the future.