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The Castagnoli–Cushman reaction was carried out with various fused and bridged bicyclic anhydrides. The influence of the anhydride nature and, specifically, the size of fused anhydride rings on the reaction pathway were investigated. The negative outcome of the reaction in the case of small rings and bridged systems was mechanistically described. The scope and limitations of the procedure involving anhydrides and imines were discussed. The high diastereoselectivity of the method was proved and showed its correlation with the previous results. The reaction was optimized and scaled up to afford multigram amounts of products in a single run (up to 50 g). [ABSTRACT FROM AUTHOR]

Compounds bearing structurally unique isoquinolin-1(2H)-one scaffold were found to be widely distributed in various organisms and they exhibited a broad spectrum of biological activities. In the present study, 22 derivatives of the isoquinolin-1(2H)-one scaffold were synthesized by Castagnoli- Cushman reaction and esterification reaction and their antifungal activity was evaluated against 7 phytopathogens. The in vitro bioassay results indicated that the mycelial growth inhibition rates of compounds 5a-5k and 6a-6f were higher than 80% against Sclerotinia sclerotiorum at the concentration of 100 μg/mL. Compound 5k was the most potent activity with the EC50 value of 5.8 μg/mL, which was lower than the commercial boscalid (EC50 = 0.094 μg/mL). The structure-activity relationship analysis revealed that the phenyl on N atom site is superior to the alkyl, and the introduction of different substituents to the phenyl group could improve the antifungal activity, which was subject to the positional selectivity and the number of substituents on the phenyl group. However, introducing different substituents at C3 phenyl and C4 carboxyl group were unfavorable for the activity. The preventive control efficacy of 5k was 94.6% at 500 μg/mL, which was comparable to that of boscalid at 10 μg/mL (95.8%). Taken together, these results could provide some important cues for further optimization of tetrahydroisoquinolone-4-carboxylic acid derivatives. [ABSTRACT FROM AUTHOR]

Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli–Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic purification. These findings significantly extend the range of cyclic anhydrides employable in the Castagnoli–Cushman reaction and signify access to a novel substitution pattern around the medicinally relevant tetrahydroisoquinolonic acid scaffold. [ABSTRACT FROM AUTHOR]

Based on the previously reported involvement of homophthalic acid monoesters in the Castagnoli–Cushman reaction-type cyclocondensation with imines, we tested a number of other o-methyl benzoic acids bearing various electron-withdrawing groups in the α-position. The majority of these substrates delivered the expected tetrahydroisoquinolone adducts on activation with CDI or acetic anhydride. Homophthalic acid mononitriles displayed the highest promise as substrates for the new reaction, both in terms of scope and product yields. Homophthalic acid monoamides either gave low yields or failed to react with imines. Sulfonyl-substituted substrates gave the desired (and hitherto unknown) type of tetrahydroisoquinolines. Despite the low yields, this approach to sulfonyl-substituted tetrahydroisoquinolines appears practical as alternative syntheses based on the traditional, carboxylic acid CCR adducts would presumably be cumbersome and multistep. The azido- and nitro-substituted o-methyl benzoic acids failed to react with imines. [ABSTRACT FROM AUTHOR]

Screening of a library of novel N-hydroxylactams amenable by the Castagnoli-Cushman reaction identified four lead compounds that facilitated 55Fe transport into P. aeruginosa cells (one of these synthetic siderophores was found to be as efficient at promoting iron uptake as the natural siderophores pyoverdine, pyochelin or enterobactin). Conjugates of the four lead siderophores with ciprofloxacin were tested for antibacterial activity against P. aeruginosa POA1 (wild type) and the ∆pvdF∆pchA mutant strain. The antibacterial activity was found to be pronounced against the ∆pvdF∆pchA mutant strain grown in CAA medium but not for the POA1 strain. This may be indicative of these compounds being 'Trojan horse' antibiotics. Further scrutiny of the mechanism of the antibacterial action of the newly developed conjugates is warranted. [ABSTRACT FROM AUTHOR]

The reactivity pattern of the Castagnoli‐Cushman reaction between homophthalic anhydride and imines was completely reproduced by replacing homophthalic anhydride with o‐(alkoxycarbonyl)methyl benzoic acids activated by CDI (1,1′‐carbonyldiimidazole). This allows obtaining tetrahydroisoquinolonic esters directly and plants the Castagnoli‐Cushman chemistry onto a fundamentally new reagent space not requiring the use of cyclic anhydrides. [ABSTRACT FROM AUTHOR]

An earlier described three-component variant of the Castagnoli-Cushman reaction employing homophthalic anhydrides, carbonyl compound and ammonium acetate was applied towards the preparation of 1-oxo-3,4-dihydroisoquinoline-4-carboxamides with variable substituent in position 3. These compounds displayed inhibitory activity towards poly(ADP-ribose) polymerase (PARP), a clinically validated cancer target. The most potent compound (PARP1/2 IC50 = 22/4.0 nM) displayed the highest selectivity towards PARP2 in the series (selectivity index = 5.5), more advantageous ADME prameters compared to the clinically used PARP inhibitor Olaparib.

A novel 3,4-dihydroisoquinol-1-one-4-carboxamide scaffold was designed as the basis for the development of novel inhibitors of poly(ADP-ribose) polymerase (PARP). Synthesis of 3,4-dihydroisoquinol-1-one-4-carboxylic acids was achieved using the previously developed protocol based on the modified Castagnoli-Cushman reaction of homophthalic anhydrides and 1,3,5-triazinanes as formaldimine synthetic equivalents. Employment of 2,4-dimethoxy groups on the nitrogen atom of the latter allowed preparation of 2,3-unsubatituted 3,4-dihydroquinolone core building blocks. Iterative synthesis and in vitro biological testing of the amides resulting from the amidation of these carboxylic acids allowed not only drawing important structure-activity generalisations (corroborated by in silico docking simulation) but also the identification of the lead compound, 4-([1,4'-bipiperidine]-1'-carbonyl)-7-fluoro-3,4-dihydroisoquinolin-1(2H)-one, as the candidate for further preclinical development. The lead compound as well as its des-fluoro analog were compared to the approved PARP1 inhibitor, anticancer drug Olaparib, in terms of their molecular characteristics defining druglikeness as well as experimentally determined ADME parameters. The newly developed series demonstrated clear advantages over Olaparib in terms of molecular weight, hydrophilicity, human liver microsomal and plasma stability as well as plasma protein binding. Further preclinical investigation of the lead compound is highly warranted.

3‐Aryl glutaric acid anhydrides have been explored as substrates for the Castagnoli‐Cushman reaction with imines. A series of 3‐aryl glutaric acids was synthesized according to literature protocols and introduced into the reaction with imines in the presence of acetic anhydride. The latter acted as a dehydrating agent leading to in situ generation of a cyclic anhydride from the dicarboxylic acid starting material. Reassuringly, the reaction gave the desired δ‐lactams with three newly created stereocenters as predominantly one diastereomer whose relative configuration was established by single‐crystal X‐ray crystallography. [ABSTRACT FROM AUTHOR]

A novel 3,4-dihydroisoquinol-1-one-4-carboxamide scaffold was designed as the basis for the development of novel inhibitors of poly(ADP-ribose) polymerase (PARP). Synthesis of 3,4-dihydroisoquinol-1-one-4-carboxylic acids was achieved using the previously developed protocol based on the modified Castagnoli-Cushman reaction of homophthalic anhydrides and 1,3,5-triazinanes as formaldimine synthetic equivalents. Employment of 2,4-dimethoxy groups on the nitrogen atom of the latter allowed preparation of 2,3-unsubatituted 3,4-dihydroquinolone core building blocks. Iterative synthesis and in vitro biological testing of the amides resulting from the amidation of these carboxylic acids allowed not only drawing important structure-activity generalisations (corroborated by in silico docking simulation) but also the identification of the lead compound, 4-([1,4'-bipiperidine]-1'-carbonyl)-7-fluoro-3,4-dihydroisoquinolin-1(2H)-one, as the candidate for further preclinical development. The lead compound as well as its des-fluoro analog were compared to the approved PARP1 inhibitor, anticancer drug Olaparib, in terms of their molecular characteristics defining druglikeness as well as experimentally determined ADME parameters. The newly developed series demonstrated clear advantages over Olaparib in terms of molecular weight, hydrophilicity, human liver microsomal and plasma stability as well as plasma protein binding. Further preclinical investigation of the lead compound is highly warranted. [ABSTRACT FROM AUTHOR]

An earlier described three-component variant of the Castagnoli-Cushman reaction employing homophthalic anhydrides, carbonyl compound and ammonium acetate was applied towards the preparation of 1-oxo-3,4-dihydroisoquinoline-4-carboxamides with variable substituent in position 3. These compounds displayed inhibitory activity towards poly(ADP-ribose) polymerase (PARP), a clinically validated cancer target. The most potent compound (PARP1/2 IC50 = 22/4.0 nM) displayed the highest selectivity towards PARP2 in the series (selectivity index = 5.5), more advantageous ADME prameters compared to the clinically used PARP inhibitor Olaparib. [ABSTRACT FROM AUTHOR]

The Castagnoli–Cushman reaction of 3,4-dihydroisoquinolines with glutaric anhydride, its oxygen and sulfur analogues was investigated as a one-step approach to the benzo[a]quinolizidine system and its heterocyclic analogs. An extension towards the pyrrolo[2,1-a]isoquinoline system was achieved with the use of succinic anhydride. The results are evidence of an unexplored method for the access of the aforementioned tricyclic annelated systems incorporating a bridgehead nitrogen atom. The structures and relative configurations of the new compounds were established by means of 1D and 2D NMR techniques. The reactions between 1-methyldihydroisoquinoline and glutaric, diglycolic and succinic anhydrides yielded unexpected isoquinoline derivatives containing an exocyclic double bond. The compounds prepared bear the potential to become building blocks for future synthetic bioactive molecules.

Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli–Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic purification. These findings significantly extend the range of cyclic anhydrides employable in the Castagnoli–Cushman reaction and signify access to a novel substitution pattern around the medicinally relevant tetrahydroisoquinolonic acid scaffold.

Based on the previously reported involvement of homophthalic acid monoesters in the Castagnoli–Cushman reaction-type cyclocondensation with imines, we tested a number of other o-methyl benzoic acids bearing various electron-withdrawing groups in the α-position. The majority of these substrates delivered the expected tetrahydroisoquinolone adducts on activation with CDI or acetic anhydride. Homophthalic acid mononitriles displayed the highest promise as substrates for the new reaction, both in terms of scope and product yields. Homophthalic acid monoamides either gave low yields or failed to react with imines. Sulfonyl-substituted substrates gave the desired (and hitherto unknown) type of tetrahydroisoquinolines. Despite the low yields, this approach to sulfonyl-substituted tetrahydroisoquinolines appears practical as alternative syntheses based on the traditional, carboxylic acid CCR adducts would presumably be cumbersome and multistep. The azido- and nitro-substituted o-methyl benzoic acids failed to react with imines.

Sulfamide was desymmetrized by a reaction with aldehydes to give N -sulfamoylimines. The latter reagents were successfully introduced into diastereo- and chemoselective transformation with cyclic anhydride using the Castagnoli-Cushman reaction to give unprotected N -sulfamoyl tetrahydroisoquinolonic (THIQ) acids under simple metal-free protocol. Thereby, the first general approach to the direct assembly of six-membered N -sulfamoyl lactams was developed. The synthesized compounds belong to representative, drug-like chemotypes with their well-defined three-dimensional structures and tunable physicochemical properties. In an attempt to probe their pharmacological potential, the newly synthesized lactams were screened against therapeutically relevant human and bacterial carbonic anhydrases, with some derivatives showing low micromolar enzyme inhibitory profiles. [Display omitted] [ABSTRACT FROM AUTHOR]

Screening of a library of novel N-hydroxylactams amenable by the Castagnoli-Cushman reaction identified four lead compounds that facilitated 55Fe transport into P. aeruginosa cells (one of these synthetic siderophores was found to be as efficient at promoting iron uptake as the natural siderophores pyoverdine, pyochelin or enterobactin). Conjugates of the four lead siderophores with ciprofloxacin were tested for antibacterial activity against P. aeruginosa POA1 (wild type) and the ∆pvdF∆pchA mutant strain. The antibacterial activity was found to be pronounced against the ∆pvdF∆pchA mutant strain grown in CAA medium but not for the POA1 strain. This may be indicative of these compounds being ‘Trojan horse’ antibiotics. Further scrutiny of the mechanism of the antibacterial action of the newly developed conjugates is warranted.

A practical straightforward synthesis of medicinally important NH‐δ‐lactams through the three‐component Castagnoli‐Cushman reaction of 3‐arylglutaconic anhydrides with carbonyl compound and ammonium acetate has been developed. The scope of the protocol has been thoroughly explored paying particular attention to the carbonyl component using wide array of aliphatic and aromatic aldehydes as well as rarely involved cyclic and acyclic ketones. Synthetic potential of prepared compounds was demonstrated by a series of post‐modifications, including unexpected isomerization. [ABSTRACT FROM AUTHOR]

Lactams are essential compounds in medicinal chemistry and key intermediates in the synthesis of natural products. The Castagnoli–Cushman reaction (CCR) of homophthalic anhydride with imines is an exciting method for accessing cyclic densely substituted lactam products. Most CCRs need to be catalyzed or heated. Herein, we report a new, efficient, metal and catalyst-free CCR for the synthesis of poly-substituted 3,4-lactams utilizing the unique properties of trifluoroethanol (TFE). This procedure provides high-speed and smooth access to a broad range of densely substituted 3,4-lactams in good yields and a 100% atom-economical fashion.

The earlier described reaction of homophthalic anhydrides with aromatic ketones and ammonium acetate was tested for cyclic ketones (yielding spirocyclic motifs) and aliphatic aldehydes. In contrast to previous findings, the reaction was found to require no catalyst at all and to be applicable, in the non-catalyzed format, to these new carbonyl substrates as well as aromatic ketones. The reaction typically proceeds with high diastereoselectivity; if not, the initial diastereomeric mixture can be quantitatively equilibrated into a single, trans -diastereomer on treatment with aqueous base. [ABSTRACT FROM AUTHOR]

[Display omitted] A highly efficient telescopic synthesis of a nitrogen-fused heterocycle dihydrodibenzonapthyridinedione has been developed via imine formation, then the Castagnoli-Cushman reaction followed by nitro-reduction and intramolecular lactamization starting from 2-nitrobenzaldehyde, aliphatic/aromatic amines, and homophthalic anhydride. This one-pot stepwise synthesis strategy offers a practical and simple approach to produce structurally diverse dihydrodibenzonaphthyridinediones without isolating intermediates. [ABSTRACT FROM AUTHOR]

A series of 15 benzene-fused hexahydropyrrolo[1,2-b]isoquinolonic acids with substantial degree of steric encumbrance has been prepared via a novel variant of the Castagnoli–Cushman reaction of homophthalic anhydride (HPA) and various indolenines. The employment of a special kind of a cyclic imine component reaction allowed, for the first time, isolating a Mannich-type adduct between HPA and an imine component which has been postulated but never obtained in similar reactions.

The multicomponent Castagnoli‐Cushman reaction followed by post‐condensational modifications allowed for a flexible, modular construction of fluorescent chemosensor compounds. When tested against a panel of fourteen metal ions, one of the eight compounds investigated in this work was found to selectively respond to Cu2+ ions by fluorescence quenching (thus being a "turn‐off" chemosensor for this metal). Another compound was found to produce fluorescence increase in response to Pb2+ ions. Interestingly, the sensitivity of this "turn‐on" chemosensor to lead(II) ions was unaffected by the presence of a large excess of other metals. Analysis of the structure‐sensing property relationships of these sensors allowed developing a general understanding of the factors influencing the chemosensor properties. All of the critical structural factors employed in the chemosensor design were found to be important for the metal sensing and selectivity. These findings will allow designing next‐generation chemosensors based on the same modular construction approach in the future. [ABSTRACT FROM AUTHOR]

A novel approach to indolo[3,2-c]isoquinoline and dibenzo[c,h][1,6]naphthyridine tetracyclic systems was discovered based on switchable reduction of 2-methoxy-3-(2-nitrophenyl)-1-oxo-1,2,3,4-tetrahydroisoquinoline-4-carboxylic acid prepared via Castagnoli–Cushman reaction. Reduction with ammonium formate resulted in the expected selective transformation of the nitro group (thus providing access to substituted dibenzo[c,h][1,6]naphthyridine via cyclization and dehydrogenation). However, attempted reduction with sodium sulfide initiated a previously unknown reaction cascade including double reduction, cyclization, and decarboxylation, leading to formation of indolo[3,2-c]isoquinoline polyheterocycle in one synthetic step.

Graphical abstract Highlights • 1,2,3,4-Tetrahydropyrazino[1,2- a ]indole core is featured in many bioactive compounds. • A novel approach to this privileged core is described. • An unsuccessful Castagnoli-Cushman reaction toward this core was rendered workable. • It involves the use of indole-based dicarboxylic acid and acetic anhydride. • It dehydrates the diacid into its cyclic anhydride which enters the reaction. Abstract Indole-fused cyclic anhydrides earlier deemed unreactive in the Castagnoli-Cushman reaction with imines have been rendered valid participant in this process. The new reaction format involves the use of respective indole-based dicarboxylic acids and in situ cyclodehydration of the latter by acetic anhydride. This finding validates a fundamentally new approach to synthesizing compounds based on the privileged 1,2,3,4-tetrahydropyrazino[1,2- a ]indole core characterized by hitherto undescribed substitution pattern. [ABSTRACT FROM AUTHOR]

Hitherto undescribed 3-unsubstituted tetrahydroisoquinolonic acids (isolated as their respective methyl esters) were accessed for the first time by the uncatalyzed, thermally promoted Castagnoli- Cushman reaction (CCR) of homophthalic anhydride (HPA) and a series of 1,3,5-triazinanes. The moderate yields observed in some cases are most likely associated with a persistent impurity also formed in these reactions. The new scaffold is expected to find novel medicinal utility (compared to the traditional CCR adducts) because it lacks a substituent at the 3-position. [ABSTRACT FROM AUTHOR]

Pyrazole-fused cyclic anhydrides have been employed for the first time as the Castagnoli–Cushman reaction partners to produce hitherto unknown 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-7-carboxylates in remarkably convenient and speedy fashion. Attempts to realize the same chemistry with indole and benzimidazole analogues failed.Pyrazole-fused cyclic anhydrides have been employed for the first time as the Castagnoli–Cushman reaction partners to produce hitherto unknown 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-7-carboxylates in remarkably convenient and speedy fashion. Attempts to realize the same chemistry with indole and benzimidazole analogues failed.Pyrazole-fused cyclic anhydrides have been employed for the first time as the Castagnoli–Cushman reaction partners to produce hitherto unknown 4-oxo-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine-7-carboxylates in remarkably convenient and speedy fashion. Attempts to realize the same chemistry with indole and benzimidazole analogues failed. [ABSTRACT FROM AUTHOR]

The first application of multicomponent chemistry (the Castagnoli-Cushman reaction) toward the convenient one-step preparation of cyclic hydroxamic acids is described. Cyclic hydroxamic acids are close analogues of bacterial siderophores (iron-binding compounds) and form stable complexes with Fe3+ ions as confirmed by spectrophotometric measurements. These compounds are potential components for the design of chelating agents for iron overload disease therapy, as well as siderophore-based carrier systems for antibiotic delivery across the bacterial cell wall. [ABSTRACT FROM AUTHOR]

Cyclic hydroxamic acids can be viewed as effective binders of soluble iron and can therefore be useful moieties for employing in compounds to treat iron overload disease. Alternatively, they are analogs of bacterial siderophores (iron-scavenging metabolites) and can find utility in designing antibiotic constructs for targeted delivery. An earlier described three-component variant of the Castagnoli—Cushman reaction of homophthalic acid (via in situ cyclodehydration to the respective anhydride) was extended to involve hydroxylamine in lieu of the amine component of the reaction. Using hydroxylamine acetate and O-benzylhydroxylamine was key to the success of this transformation due to greater solubility of the reagents in refluxing toluene (compared to hydrochloride salt). The developed protocol was found suitable for multigram-scale syntheses of N-hydroxy- and N-(benzyloxy)tetrahydroisoquinolonic acids. The cyclic hydroxamic acids synthesized in the newly developed format have been tested and shown to be efficient ligands for Fe3+, which makes them suitable candidates for the above-mentioned applications.

A new format for the Castagnoli-Cushman reaction of structurally diverse dicarboxylic acids, amines, and aldehydes in the presence of acetic anhydride as dehydrating agent is described. The reaction is distinctly amenable to parallel format: the combinatorial array of 180 reactions delivered 157 products of >85% purity without chromatographic purification (of this number, 143 compounds had >94% purity). The new method offers a convenient preparation of the skeletally and peripherally diverse, lead- and druglike γ- and δ-lactam carboxylic acids with high diastereoselectivity in combinatorial fashion. [ABSTRACT FROM AUTHOR]

Attempted reaction of indolenines (which represent rather sterically hindered cyclic imines) with a series of dicarboxylic acid anhydrides yielded no expected product, the Castagnoli-Cushman lactam. Instead, products presumably formed via N -acyliminium species trapping by a carboxylate anion. Among them, hydrolytically labile 2:2 adducts of an indolenine and a cyclic anhydride, containing a 16-membered cyclic core, are particularly intriguing. This result contradicts the recently reported successful Castagnoli-Cushman reaction of indolenines with homophthalic anhydride suggesting a mechanistic switch in the course of the reaction. [ABSTRACT FROM AUTHOR]

The diversity of lactam products accessible by the Castagnoli-Cushman reaction (CCR) of imines and dicarboxylic acid anhydrides has been extended to privileged ε-lactams. This novel variant of the CCR using o-phenylenediacetic anhydride is often high-yielding and remarkably diastereoselective and allows the use of α-C-H imines. [ABSTRACT FROM AUTHOR]

Castagnoli-Cushman reaction of imines derived from 2-chloropyridine-3-carboxaldehyde with a cyclic anhydride (4-(methylsulfonyl)-morpholine-2,6-dione) conducted at 110°C in DMF over 1 h, as expected, led to a mixture of trans- and cis-configured carboxylic acids. However, the latter underwent a spontaneous intramolecular reaction of the carboxylic functionality onto the labile nearby 2-chloropyridine moiety to give the respective tricyclic lactones in 17-23% yield, along with 41-68% yield of the uncyclized trans-configured products (isolated as methyl esters). [ABSTRACT FROM AUTHOR]

[Display omitted] Rare cis-configured 2,4-disubstituted 1-alkylpyridines were envisioned as ligands for trace amine associated receptor 1 (TAAR1). They were synthesized in diastereomerically pure form with the decarboxylative Castagnoli–Cushman reac-tion followed by two reduction events. Despite showing no affinity to TAAR1 as was anticipated, these novel, druglike and CNS-focused compounds will be of much utility in sub-sequent lead generation pursuits. [ABSTRACT FROM AUTHOR]

Lactams are essential compounds in medicinal chemistry and key intermediates in the synthesis of natural products. The Castagnoli–Cushman reaction (CCR) of homophthalic anhydride with imines is an exciting method for accessing cyclic densely substituted lactam products. Most CCRs need to be catalyzed or heated. Herein, we report a new, efficient, metal and catalyst-free CCR for the synthesis of poly-substituted 3,4-lactams utilizing the unique properties of trifluoroethanol (TFE). This procedure provides high-speed and smooth access to a broad range of densely substituted 3,4-lactams in good yields and a 100% atom-economical fashion. [ABSTRACT FROM AUTHOR]

Four anhydrides of 1-(carboxymethyl)pyrrole-2-carboxylic acids bearing electron-withdrawing substituents at positions 6 or 7 of the bicyclic system have been investigated in the Castagnoli–Cushman reaction with imines. 6-Benzoyl- and 7-sulfamoyl-substituted anhydrides demonstrated lower reactivity while 7-benzoyl derivative displayed broader substrate scope. These findings have been rationalized from the mechanistic perspective. [ABSTRACT FROM AUTHOR]

[Display omitted] • 6,7,8,9-Tetrahydropyrido[3′,2′:4,5]pyrrolo[1,2- a ]pyrazines cores are featured in many bioactive compounds. • A novel approach to these privileged cores is described. • Microwave irradiation enriched Castagnoli-Cushman Reaction effectiveness and faster reaction times. • It involves the use of azaindole dicarboxylic acid and acetic anyhydride. • It dehydrates the diacid into its cyclic anyhdride which enters the Castagnoli-Cushman Reaction. The Castagnoli-Cushman reaction of various azaindole dicarboxylic acids with imines using acetic anhydride as a dehydrating agent was significantly accelerated by microwave irradiation. The reaction conditions offer a convenient preparation of novel 6,7,8,9-tetrahydropyrido[3′,2′:4,5]pyrrolo[1,2- a ]pyrazines in moderate to good yields with good trans stereoselectivity. [ABSTRACT FROM AUTHOR]

• The Castagnoli-Cushman reaction of dicarboxylic acids proceeds through anhydride. • 2,2′-(Cyclopentane-1,1-diyl)diacetic acid was previously found poorly reactive. • Introduction of two sulfur atoms in the cyclopentane portion enhanced reactivity. • The enhancement is likely due to the stabilization of the anhydride's enol form. • The observed reactivity trend was corroborated by DFT calculations. 8-Oxa-1,4-dithiaspiro[4.5]decane-7,9-dione and 9-oxa-1,5-dithiaspiro[5.5]undecane-8,10-dione, cyclic anhydrides formed in situ from the respective dicarboxylic acids in the presence of acetic anhydride, possess an enhanced reactivity and display a broad substrate scope in the Castagnoli-Cushman reaction with imines. [ABSTRACT FROM AUTHOR]

Three component Castagnoli-Cushman reaction of homophthalic anhydride, cyclic ketones and ammonium acetate followed by decarboxylation and lactam reduction provided the shortest reported route to spirocyclic tetrahydroisoquinolines (spiroTHIQs). • Tetrahydroisoquinolines (THIQs) are privileged motifs for drug design. • THIQs containing a spiro center at position 3 are scarce. • Such scaffolds have been accessed via a three-step approach. • Step 1: the recently developed variant of the Castagnoli-Cushman reaction. • Steps 2–3: decarboxylation followed by lactam reduction. A new route to privileged spirocyclic tetrahydroisoquinolines (spiroTHIQs) has been developed. The key step in which the spirocyclic system is formed in generally good yields and diastereoselectivity is the three-component Castagnoli-Cushman reaction of homophthalic anhydride, cyclic ketones and ammonium acetate. Decarboxylation of the initial adduct yields THIQ lactams which are reduced by lithium aluminum hydride. The route is shorter, more convergent and operationally simpler than the previously reported syntheses of similar spirocyclic building blocks. [ABSTRACT FROM AUTHOR]

A novel approach to indolo[3,2-c]isoquinoline and dibenzo[c,h][1,6]naphthyridine tetracyclic systems was discovered based on switchable reduction of 2-methoxy-3-(2-nitrophenyl)-1-oxo-1,2,3,4-tetrahydroisoquinoline-4-carboxylic acid prepared via Castagnoli–Cushman reaction. Reduction with ammonium formate resulted in the expected selective transformation of the nitro group (thus providing access to substituted dibenzo[c,h][1,6]naphthyridine via cyclization and dehydrogenation). However, attempted reduction with sodium sulfide initiated a previously unknown reaction cascade including double reduction, cyclization, and decarboxylation, leading to formation of indolo[3,2-c]isoquinoline polyheterocycle in one synthetic step. [ABSTRACT FROM AUTHOR]

A short synthesis of 2- N -hydroxy-3,4-dihydroisoquinol-2-one has been devised, which is based on the Castagnoli-Cushman reaction and 3 times more high-yielding compared to an earlier reported sequence. [ABSTRACT FROM AUTHOR]

The Castagnoli-Cushman reaction of 3,4-dihydroisoquinolines with glutaric anhydride, its oxygen and sulfur analogues was investigated as a one-step approach to the benzo[ a ]quinolizidine system and its heterocyclic analogs. An extension towards the pyrrolo[2,1- a ]isoquinoline system was achieved with the use of succinic anhydride. The results are evidence of an unexplored method for the access of the aforementioned tricyclic annelated systems incorporating a bridgehead nitrogen atom. The structures and relative configurations of the new compounds were established by means of 1D and 2D NMR techniques. The reactions between 1-methyldihydroisoquinoline and glutaric, diglycolic and succinic anhydrides yielded unexpected isoquinoline derivatives containing an exocyclic double bond. The compounds prepared bear the potential to become building blocks for future synthetic bioactive molecules., (Copyright © 2020, Pashev et al.; licensee Beilstein-Institut.)

By exploiting the power of multicomponent chemistry, a relatively small, diverse set of primary sulfonamides was synthesized and screened against a panel of human carbonic anhydrases to reveal a low-nanomolar, albeit non-selective h CA IV lead inhibitor. Investigation of the docking poses of this compound identified a hydrophilic pocket unique to h CA IV and conveniently positioned near the carboxylate functionality of the initial lead. Various residues capable of forming hydrogen bonds as well as salt bridges were placed in this pocket via a carboxamides linkage, which led to drastic improvement of potency and selectivity towards h CA IV. This improvement of the desired inhibitory profile was rationalized by the new contacts as had been envisioned. These new tool compounds were shown to possess selective, dose-dependent cytotoxicity against human glioma T98G cell line. The latter showed a substantially increased h CA IV mRNA expression under hypoxic conditions. Image 1 • Selective inhibitors of human carbonic anhydrase IV (h CA IV) are rare. • The power of multicomponent chemistry was exploited. • Sulfonamides derived from the Castagnoli-Cushman reaction were prepared. • Initial non-selective nanomolar lead was optimized using in silico docking. • New compounds demonstrated selective, subnanmolar inhibition of h CA IV. [ABSTRACT FROM AUTHOR]

• o -Nitrobenenesulfonyl (o -Ns) protected piparzin-2-ones were synthesized previously. • These are products of the Castagnoli-Cushman reaction. • The o -Ns group was viewed as a building block this time. • The reduction of the nitro group followed HATU-promoted lactamization was efficient. • New seven-membered sultam-lactams are related to several biologically active compounds. Downstream modification of piperazin-2-ones obtained by the Castagnoli-Cushman reaction leads to a novel version of the medicinally relevant 1,2,5-benzothiadiazepin-4-one-1,1-dioxide scaffold. The relative stereochemistry remained trans as evidenced by the spectroscopic data and the single-crystal X-ray analysis. [ABSTRACT FROM AUTHOR]

Cyclic hydroxamic acids can be viewed as effective binders of soluble iron and can therefore be useful moieties for employing in compounds to treat iron overload disease. Alternatively, they are analogs of bacterial siderophores (iron-scavenging metabolites) and can find utility in designing antibiotic constructs for targeted delivery. An earlier described three-component variant of the Castagnoli—Cushman reaction of homophthalic acid (via in situ cyclodehydration to the respective anhydride) was extended to involve hydroxylamine in lieu of the amine component of the reaction. Using hydroxylamine acetate and O-benzylhydroxylamine was key to the success of this transformation due to greater solubility of the reagents in refluxing toluene (compared to hydrochloride salt). The developed protocol was found suitable for multigram-scale syntheses of N-hydroxy- and N-(benzyloxy)tetrahydroisoquinolonic acids. The cyclic hydroxamic acids synthesized in the newly developed format have been tested and shown to be efficient ligands for Fe3+, which makes them suitable candidates for the above-mentioned applications. [ABSTRACT FROM AUTHOR]