Asymmetric Total Synthesis of (+)-21-epi-Eburnamonine Via a Photocatalytic Radical Cascade Reaction

An asymmetric total synthesis of(+)-21-epi-eburnamonine has been achieved.Key features of the synthesis include a visible-light photocatalytic intra-/intramolecular radical cascade reaction to assemble the tetracyclic ABCD ring system,and a highly diastereoselective Johnson-Claisen rearrangement to establish the C20 all-carbon quaternary stereocenter.

Catalytically generated noncovalent ammonium dienolate:a versatile platform for the development of organocatalytic asymmetric cascade reactions

Organocatalytic cascade reactions represent a powerful strategy for the rapid construction of complex chiral molecules with multiple stereocenters from simple substrates under mild conditions. The intriguing structural feature and diverse reactivity of catalytically generated dienolate species render them competent and versatile intermediates for the development of practical and valuable cascade reactions. Over the past years, a plethora of innovative and pioneering noncovalent ammonium dienolatemediated cascade reactions have been designed and implemented under the catalysis of chiral organocatalysts, making dienolate activation a general, robust, and complementary method for the functionalization of unsaturated carbonyl compounds and related substances. This review illustrates the recent advances in organocatalytic noncovalent ammonium dienolate-mediated cascade reactions(mainly from 2010 to 2023), including the cascade transformations of ammonium dienolates directly generated from unsaturated ketone/aldehyde, ester/lactone/azlactone, amide/lactam/pyrazolone/oxindole, and alkylidene nitrile compounds. The contents are arranged based on the reaction types of the ammonium dienolates, with an emphasis on cascade 2,5-, 3,5-, and 4,5-difunctionalizations of these intermediates. Furthermore, other cascade reactions involving the 1,3-, 2,3-, and even more complex 3,4,5-reactivities of ammonium dienolates were also discussed. The reaction pathway, reaction stereoinduction, and synthetic applications of the ammonium dienolate-mediated cascade reactions were highlighted throughout the article. As a stimulating and ever-growing research area, the organocatalytic noncovalent ammonium dienolate-mediated cascade reactions are expected to continue demonstrating their magic power for constructing chiral targets in the future and further expanding the boundaries of asymmetric catalysis.

Anion cascade reactions Ⅲ:Synthesis of 3-isoquinuclidone bridged polycyclic lactams

Bridged polycyclic lactams are important structural units in organic functional materials,natural products,and pharmaceuticals.A flexible and efficient anion cascade reaction was developed for the preparation of bridged polycyclic lactams from readily available malonamides and 1,4‑dien-3-ones.Various highly substituted bridged polycyclic lactams were synthesized in good to excellent yields by tandem nucleophilic sequences in the presence of t BuOK in commercially available EtOH solvent at 60℃.Notably,the simple reactions can be run on a gram scale.Mechanistically,bis-Michael addition reaction and hemiaminalization reactions are involved in the tandem transformation.

Designed imidazole-based supramolecular catalysts for accelerating oxidation/hydrolysis cascade reactions

Reconstructing enzymatic active sites presents a significant challenge due to the intricacies involved in achieving enzyme-like scaffold folding and spatial arrangement of essential functional groups.There is also a growing interest in building biocatalytic networks,wherein multiple enzymatic active sites are localized within a single artificial system,allowing for cascaded transformations.In this work,we report the self-assembly of imidazole or its derivatives with fluorenylmethyloxycarbonyl-modified histidine and Cu2+to fabricate a supramolecular catalyst,which possesses catechol oxidase-like dicopper center with multiple imidazole as the coordination sphere.Transmission electron microscopy,low-temperature X-band continuous-wave electron paramagnetic resonance,K-edge X-ray absorption spectra/the extended X-ray absorption fine structure analysis,and density functional theory modeling were used for the structural characterization of the catalyst.The phenol derivatives and the dissolved oxygen were used as the substrates,with the addition of 4-aminoantipyrine to generate a red adduct with a maximum absorbance at 510 nm,for obtaining time-dependent absorbance change curves and estimating the activities.The results reveal that the addition of imidazole synergistically accelerates the oxidative activity about 10-fold and the hydrolysis activity about 14-fold than fluorenylmethyloxycarbonyl modified-histidine/Cu2+.The supramolecular nanoassembly also exhibits the ability to catalyze oxidation/hydrolysis cascade reactions,converting 2′,7′-dichlorofluorescin diacetate into 2′,7′-dichlorofluorescein.This process can be regulated through the methylation of the imidazole component at various positions.This work may contribute to the design of advanced biomimetic catalysts,and shed light on early structural models of the active sites of the primitive copper-dependent enzymes.

Highly selective synthesis of functionalized morphan derivatives through a multi-component cascade reaction of 3-formylchromones, 2-naphthols, and enaminones

A novel protocol for the preparation of highly functionalized 2-azabicyclo[3.3.1]nonane(morphan)derivatives via a multicomponent cascade reaction,involving 3-formylchromones,2-naphthols,and enaminones in the ionic liquid[BMIM]PF6 as the solvent and promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU),was developed,which involved the cleavage of one C–O bond and formation of four bonds(1 C–O,1 C–N,and 2 C–C bonds).As a result,a series of morphan derivatives were produced through a cascade reaction,including a sequence of 1,2-addition,enol-keto tautomerization,Michael addition,dehydration,another Michael addition,imine-enamine tautomerization,and N-alkylation reactions,which were accompanied by a ring-opening reaction.This protocol was suitable for combinatorial and parallel syntheses of natural product-like morphan compounds in a one-pot reaction rather than through tedious multi-step reactions.

Multicomponent cascade reaction of 3-formylchromones:Highly regioselective synthesis of functionalized pyridin-2(1H)-ones

A novel protocol was developed for the construction of highly functionalized pyridin-2(1H)-ones from 3-formylchromones,ethyl 2-(pyridin-2-yl)acetate derivatives and amines via a complex multicomponent cascade reaction involving targeted duplicated ring-opening and duplicated cyclization reactions which form skeleton-reorganized target compounds.A series of pyridin-2(1H)-ones were produced by this reaction accompanied by the formation of three bonds(one C–N and two C–C bonds)and the cleavage of one bond in one step.This protocol can be used in combinatorial and parallel syntheses of various pyridin-2(1H)-ones with potent biological activity.The advantages of this approach include simple and practical operation(multicomponent one-pot),high yields(up to 91%),and products with potential biological activity.

Integration of enzyme immobilization and biomimetic catalysis in hierarchically porous metal-organic frameworks for multi-enzymatic cascade reactions

Multiple enzymes-induced biological cascade catalysis is indispensable in biotechnology and industrial processes. Nevertheless,the drawbacks of most natural enzymes, including poor stability and recyclability and sensitivity to the environment, have hindered their broader application. Here, we report a facile strategy to prepare a biomimetic cascade reaction system by combining the advantages of enzyme immobilization and biomimetic catalysis in a one-pot reaction system based on the hierarchically porous metal-organic frameworks(HP-MOFs). The hierarchically porous zirconium-porphyrin-based MOF(HPPCN-222(Fe)) synthesized by modulator-induced strategy possessed tunable hierarchical porous and peroxidase-like activity,permitting them to act as not only an efficient immobilization matrix for glucose oxidase(GOx) but also peroxidase mimics to catalyze the cascade for glucose detection. A stable, anti-interference and reusable colorimetric biosensor for glucose detection was successfully established through GOx@HP-PCN-222(Fe) on the basis of the artificial tandem catalysis. Moreover, the GOx@HP-PCN-222(Fe)-fabricated electrode was available for glucose detection by electrochemical method. This work provides a potentially universal method to design functional multi-enzymatic cascade reaction systems by integrating the merits of enzyme encapsulation and biomimetic catalysis in HP-MOFs.

A compact fluorescence/circular dichroism dual-modality probe for detection, differentiation, and detoxification of multiple heavy metal ions via bond-cleavage cascade reactions

Selective detection of multiple analytes in a compact design with dual-modality and theranostic features presents great challenges. Herein, we wish to report a coumarin-thiazolidine masked D-penicillamine based dual-modality fluorescent probe COU-DPA-1 for selective detection, differentiation, and detoxification of multiple heavy metal ions(Ag^(+), Hg^(2+), Cu^(2+)). The probe shows divergent fluorescence(FL)/circular dichroism(CD) responses via divergent bond-cleavage cascade reactions(metal ion promoted C-S cleavage and hydrolysis at two distinctive cleavage sites): FL “turn-off” and CD “turn-on” for Ag+(no hydrolysis), FL “turn-on” and CD “turn-off” for Hg^(+)(imine hydrolysis), and FL “self-threshold ratiometric” and CD “turn-off” for excess Cu^(2+)(lactone and imine hydrolysis), providing the first example of a fluorescence/CD dual-modality probe for multiple species with complimentary responses. Moreover, the bond-cleavage cascade reactions also lead to the formation of D-penicillamine heavy metal ion complexes for potential detoxification treatments.

NIR-II driven plasmon-enhanced cascade reaction for tumor microenvironment-regulated catalytic therapy based on bio-breakable Au-Ag nanozyme

Emerging nanozymes with natural enzyme-mimicking catalytic activities have inspired extensive research interests due to their high stability,low cost,and simple preparation,especially in the field of catalytic tumor therapy.Here,bio-breakable nanozymes based on glucose-oxidase(GOx)-loaded biomimetic Au–Ag hollow nanotriangles(Au–Ag–GOx HTNs)are designed,and they trigger an near-infrared(NIR)-II-driven plasmon-enhanced cascade catalytic reaction through regulating tumor microenvironment(TME)for highly efficient tumor therapy.Firstly,GOx can effectively trigger the generation of gluconic acid(H+)and hydrogen peroxide(H2O2),thus depleting nutrients in the tumor cells as well as modifying TME to provide conditions for subsequent peroxidase(POD)-like activity.Secondly,NIR-II induced surface plasmon resonance can induce hot electrons to enhance the catalytic activity of Au–Ag–GOx HTNs,eventually boosting the generation of hydroxyl radicals(•OH).Interestingly,the generated H2O2 and H+can simultaneously induce the degradation of Ag nanoprisms to break the intact triangle nanostructure,thus promoting the excretion of Au–Ag–GOx HTNs to avoid the potential risks of drug metabolism.Overall,the NIR-II driven plasmon-enhanced catalytic mechanism of this bio-breakable nanozyme provides a promising approach for the development of nanozymes in tumor therapy.

Positional assembly of multi-enzyme cascade reaction in polyelectrolyte doped microcapsule through electrospray and layer-by-layer assembly

Polyelectrolyte-doped microcapsules(PDM)was fabricated by coaxial electrospray of a mixture of glycerol and water containing 10 mg/mL cationic polyelectrolyte poly(allylamine hydrochloride)(PAH)fed as the core phase solution,and a N,N-dimethylacetylamide solution of 10 wt%polyurethane fed as the shell phase solution.Multienzyme system involving Candida Antarctica lipase B(CALB),glucose oxidase(GOD),and horseradish peroxidase(HRP)for cascade reaction was assembled in the PDM at three different places,namely,surface,shell,and lumen.Placing of enzyme inside aqueous lumen of the PDM was realized by in situ encapsulation through adding the enzyme in the core-phase solution for coaxial electrospray.By ion-pairing of enzyme with cationic surfactant CTAB,an organic soluble enzyme-CTAB complex was prepared,so that in situ embedding of enzyme in the shell of the PDM was realized by adding it into the shell phase solution.Surface attachment of enzymes was achieved by layer-by-layer(LbL)technology,which is based on the ion-exchange interactions between oppositely charged enzymes and PAH that was doped in PDM.The enzyme-decorated microcapsule was then studied as a microbioreactor,in which 1-Oxododecyla-α-glucopyranoside was converted by CALB to glucose,which was oxidised by GOD to gluconolactone in a second step.The hydrogen peroxide produced was then used by HRP to oxidize ABTS to form coloured radical cation ABTS•+for activity analysis.The successful fabrication of the PDM and precise localization of enzymes in the PDM by different strategies were fully characterized.By varying the immobilization strategy,totally six PDM bioreactors with three enzymes precisely positional assembled in different strategies were constructed and their activities for the cascade reaction were investigated and compared.The PDM micro-bioreactor prepared by novel electrospray technologies provide a smart platform for positional assembly of multi-enzyme cascade reaction in a precise and well-controlled manner.

Cascade reaction-based fluorescent probe for detection of H2S with the assistance of CTAB micelles

We report a turn-on fluorescent probe for H2S through a cascade reaction using a new trap group 4- （bromomethyl）benzoate, based on excited-state intramolecular proton transfer （ESIPT） sensing mechanism. The probe showed good selectivity and high sensitivity towards H2S and it was capable of detecting and imaging H2S in living HeLa cells, indicating its potential biological applications.

NHC-catalysed retro-aldol/aldol cascade reaction enabling solvent-controlled stereodivergent synthesis of spirooxindoles

An N-heterocyclic carbene(NHC)-catalysed retro-aldol/aldol cascade reaction of spirooxindole-basedβ-hydroxyaldehyde has been developed.The ring opening-closure process enables the diastereodivergent synthesis of spirocyclopentaneoxindole products with four consecutive stereocenters by simply changing the reaction solvents(THF or DCE).The Michael/aldol/retro-aldol/aldol sequential protocol allows the diastereodivergent synthesis of spirocyclopentaneoxindoles from 3-substituted oxindole andα,β-unsaturated aldehyde under the relay catalysis of a chiral secondary amine and an NHC catalyst.Moreover,four stereoisomers of the product can be selectively provided by using different combinations of a chiral secondary amine and a solvent.

Multisubstituted pyrazole synthesis via[3+2]cycloaddition/rearrangement/N-H insertion cascade reaction of α-diazoesters and ynones

The cascade reactions of alkyl α-diazoesters and ynones using Al(OTf)_(3) as the catalyst are described.A series of 4-substituted pyrazoles were obtained via [3+2] cycloaddition,1,5-ester shift,1,3-H shift,and N-H insertion process.Deuterium labelling experiments,kinetic studies and control experiments were carried out for the rationalization of the mechanism.

Biosynthesis of organic molecules via artificial cascade reactions based on cytochrome P450 monooxygenases

Cytochrome P450 monooxygenases(P450s)play crucial roles in the oxyfunctionalization of non-activated hydrocarbons,thus bridging the gap between simple molecules and high value-added fine chemicals.The introduction of P450s into artificially designed cascade reactions provides an exciting opportunity to accomplish challenging reactions and access organic compounds that cannot be achieved by traditional chemical catalysts or by natural metabolic pathways.The main objective of this review is to provide an overview of different types of artificially designed multi-step cascades in which P450s are involved as key catalysts in the biosynthesis of various organic molecules.The different efforts include in vitro multi-enzymatic biocatalytic cascades,in vivo biocatalytic cascades as well as chemo-enzymatic hybrid cascades.Overall,this work provides an overview of cascade reactions involving P450s with various potential applications for the industrial production of food,cosmetics,polymers and pharmaceuticals.

In Vivo Activation of Pro-Protein Therapeutics via Chemically Engineered Enzyme Cascade Reaction

Selective and temporal control over protein activity is of great importance for the advancement of the protein of interest into precise molecular medicine.Simply installing synthetic ligands to proteins for activity regulation,however,is often obscured by either nonspecificity or insufficient efficiency.This study reports a chemical approach in which enzymatic cascade reactions were designed for selective activation of pro-protein both in vitro and in vivo.Specifically,the system consisted of aromatic boronic-acid-modified nanoparticles,reactive oxygen species(ROS)-responsive pro-protein(RNase A-NBC),a small molecule drug,β-Lapachone(β-Lap),and strategically screened synthetic lipids,required for the assembly of the nanocomplexes.Once target-delivered into tumor cells,the reduction ofβ-Lap produces massive H2O2 in response to NAD(P)H quinone oxidoreductase 1(NQO1),a tumor-specific enzyme,which triggers further induction by selective chemical modification of ROS-responsive cytosolic protein ribonuclease A(RNase A)-NBC,thus,switching from“inert”pro-protein to active therapeutics,that ultimately prohibit tumor cell growth.Moreover,the designed enzymatic cascade activation of the pro-protein was effective in vivo,displaying superior therapeutic efficacy to either the pro-protein alone or theβ-Lap via tumor-targeted delivery and the consequent suppression of the tumor growth.As both RNase A andβ-Lap have been evaluated clinically as antitumor therapeutics,our chemical multi-step cascade methodology is,therefore,a promising strategy for selective modulation of pro-protein chemistry in the living system for fundamental investigations,favorable toward potential anticancer applications.

Palladium-catalyzed Cascade Cyclization-Coupling Reaction of Benzyl Halides with N, N-Diallylbenzoylamide

A novel type of palladium-catalyzed cascade cyclization-coupling reaction has been found. Reaction of N, N-diallylbenzoylamide 1 with benzyl halides 2 afforded the corresponding dihydropyrroles 3 in moderate to excellent yields.

4-Dimethylaminopyridine-catalyzed Cascade Reaction for Efficient Synthesis of Naphthofurans

A convenient and efficient method was developed for the synthesis of naphtho[2,1-blfurans via 4-dimethylaminopyridine（DMAP）-catalyzed cascade reaction of 2-hydroxy-l-naphthaldehydes and a-halogenated ketones in moderate to good yields in the presence of Na2CO3 at 80 ~C for 6 h. The mechanism for this process was briefly discussed with a tentative catalytic cycle proposed. Moreover, this method features organocatalysts and high step-economy, which makes it practical and attractive.

Concise Total Syntheses of Bioactive Alkaloids Enabled by Development or Application of Cascade Reactions:A Personnel Adventure

Design and development of new tactics and strategies to improve synthetic efficiency is a hot topic and main concern in nowadays’chemical synthesis of bioactive natural products.Cascade reactions,which construct several bonds in one step via an orchestrated sequence,have been regarded as an important tactic to rapidly increase the molecular complexity,therefor to improve the synthetic efficiency.In this perspective account,we demonstrated and highlighted the significance of cascade reaction developments and applications in concise syntheses of bioactive alkaloids based on our own recent adventure in this research field.

Temperature-controlled Cascade Reaction of Phloroglucinoltribenzyl Ether Promoted by Trifluoroacetic Anhydride and Trifluoroacetic Acid

We report the first trifluoroacetic anhydride- and trifluoroacetic acid-promoted cascade reaction with phtoroglucinoltribenzyl ether and carboxylic acid as starting materials. By simply varying the temperature of systems containing the same starting materials, different products were produced in high yields. A three-step consecutive reaction process was also proposed.

A novel and efficient strategy involving a CuI catalyzed cascade reaction to synthesize acenaphtho[1,2-b]quinoline derivatives

A novel and efficient approach for the straightforward synthesis of biologically significant acenaphtho[1,2-b]quinoline derivatives in good yields utilizing CuI as a catalyst with a broad array of substrates has been developed. The strategy features as a CuI-catalyzed cascade reaction involving the formation of two new C–C bonds and one new C–N bond with high atom economy. A proposed mechanism for the reaction is described.