Mannich reaction: A versatile and convenient approach to bioactive skeletons

Design, synthesis, and molecular docking of new phenothiazine incorporated N-Mannich bases as promising antimicrobial agents

The present work aims to synthesize four series of phenothiazine incorporation Mannich bases. Therefore, 10-methyl-10H-phenothiazine-3-sulfonamide (4) which was subjected to react with some secondary amines and formaldehyde to give the Mannich bases 5a-f, and 6-13. Compound 13 was then subjected to react with some secondary amines and formaldehyde to give the corresponding Mannich bases 14a-f. In total, twenty-two new compounds were synthesized and evaluated for in vitro growth inhibition activity against P. aeruginosa, E. coli, and S. aureus. Among the tested compounds, compounds 3, 5a, 5c, 6, 12, 13, 14d, and 14e exhibited good activity with a MIC value (12.5 μg/mL), compounds 5b, 10, 11, 14a, and 14c exhibited strong activity against the growth of S. aureus with a MIC value (6.25 μg/mL), and compound 14b superior against S. aureus with a MIC value (3.125 μg/mL) compared to drug reference ciprofloxacin with MIC value (2 μg/mL). The molecular docking investigation revealed the presence of many derivatives with high binding affinities and distinct interaction patterns with the target protein. Derivatives 14a-e emerged as the most promising possibilities, displaying the greatest binding energies and a varied variety of interaction types, including hydrogen bonding and pi interactions, over different distances, with derivative 14b exhibiting the highest binding energy at S = -8.3093 kcal/mol. These derivatives displayed superior binding affinities and various interaction mechanisms with the target protein, suggesting that they have great promise as lead compounds for future development into therapeutic medicines.

Metal-free photosensitized intermolecular carboimination of alkenes: a green and direct access to both β-amino acids and β-amino ketones

β-Amino carbonyl substructures are privileged motifs in natural products and active pharmaceutical compounds. Here, we report a photoinduced metal-free and highly regioselective intermolecular carboimination method via the simultaneous introduction of amino and carbonyl groups into the CC double bond in one step, providing straightforward, green and general access to both β-amino acid and β-amino ketone motifs from readily available alkene feedstocks. The mild reaction conditions, excellent functional group tolerance and product diversity should make this a broadly applicable carboimination approach of very broad interest to organic and medicinal chemists.

Anticancer activity of Mannich bases: a review of recent literature

This report summarizes the latest published data on the antiproliferative action and cytotoxic activity of Mannich bases, a structurally heterogeneous category of chemical entities that includes compounds which are synthesized via the grafting of an aminomethyl function onto diverse substrates by means of the Mannich reaction. The present overview of the topic is an update to the information assembled in a previously published review that covered the literature up to 2014.

Synthetic Methods and Pharmacological Potential of Different Oxazine Analogs

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Oxazine analog is a vital class of heterocyclic compounds and has attracted synthetic interest owing to their wide range of biological activities. Oxazine analogs are valuable in medicinal organic chemistry and exhibit different varieties of biological activities such as antimicrobial, anticancer, antimalarial, antitubercular, sedative, anticonvulsant, analgesic, anti-inflammatory, antipyretic, etc. Oxazine can be derived from benzene by appropriate substitution of carbon atoms of the ring by nitrogen and oxygen atoms. Nowadays, the development of drug resistance is a key problem, and to defeat this problem, it is crucial to synthesize novel compounds. So, novel oxazine analogs may play a crucial role to overcome these problems. Oxazine analogs are prepared by reaction of chalcone derivatives with thiourea in the presence of alcohol and sodium hydroxide. The present aims of this review are to give an outline of some different synthetic methods and different types of biological activities of oxazine analogs. We hope that this review will be motivating for researchers concerned with oxazine analogs.

Structure-Activity Relationships of 8-Hydroxyquinoline-Derived Mannich Bases with Tertiary Amines Targeting Multidrug-Resistant Cancer

A recently proposed strategy to overcome multidrug resistance (MDR) in cancer is to target the collateral sensitivity of otherwise resistant cells. We designed a library of 120 compounds to explore the chemical space around previously identified 8-hydroxyquinoline-derived Mannich bases with robust MDR-selective toxicity. We included compounds to study the effect of halogen and alkoxymethyl substitutions in R5 in combination with different Mannich bases in R7, a shift of the Mannich base from R7 to R5, as well as the introduction of an aromatic moiety. Cytotoxicity tests performed on a panel of parental and MDR cells highlight a strong influence of experimentally determined pK_a values of the donor atom moieties, indicating that protonation and metal chelation are important factors modulating the MDR-selective anticancer activity of the studied compounds. Our results identify structural requirements increasing MDR-selective anticancer activity, providing guidelines for the development of more effective anticancer chelators targeting MDR cancer.

Tannin-based coagulants: Current development and prospects on synthesis and uses

Population growth, industrialization, urbanization, and agriculture lead to a decrease in the availability of clean water. Coagulation/flocculation is one of the most common operations in water, urban wastewater, and industrial effluents treatment systems. Usually, this process is achieved using conventional coagulants that have their performance affected by pH, are poorly biodegradable, produce a huge volume of sludge, and are associated with degenerative diseases. As a substitute for these chemicals, natural coagulants have been highly researched for the last ten/fifteen years, especially the tannin-based (TB) ones. This review paper highlights the advantages of using these greener products to treat different types of water, wastewater, and effluents, especially from dairy, cosmetics, laundries, textile, and other industries. TB coagulants can successfully remove turbidity, color, suspended solids, soluble organic (chemical/biochemical oxygen demand) and inorganic matter (total phosphate, and heavy metals), and microorganisms. TB coagulants are compatible with other treatment technologies and can be used as coagulant-aid to reduce the consumption of chemicals. TB coagulants can reduce operating costs of water treatment due to less alkalinity consumption, as pH adjustment is sometimes unnecessary, and the production of a smaller volume of biodegradable sludge. TB coagulants can be synthesized by valorizing wastes/by-products, from the bark of some specific trees and skins/pomace of different fruits and vegetables. The strengths, weaknesses, opportunities, and threats (SWOT) on TB coagulants are discussed. The progress of TB coagulants is promising, but some threats should be overcome, especially on tannin extraction and cationization. The market competition with conventional coagulants, the feasibility of application in real waters, and the reluctance of the industries to adapt to new technologies are other weaknesses to be surpassed.

Hf(OTf)4-Catalyzed Three-Component Synthesis of N-Carbamate-Protected β-Amino Ketones

Hafnium(IV) triflate (Hf(OTf)₄) has been identified as a potent catalyst for the direct three-component synthesis of β-carbamate ketones. This new method, featuring a low catalyst loading, fast reaction rate, and solvent-free conditions, provided facile access to a diversity of carbamate-protected Mannich bases. A mechanistic investigation indicated that the three-component reaction proceeds via sequential aldol condensation and aza-Michael addition, but not the Mannich-type pathway.

Revisiting the Synthesis of Betti Bases: Facile, One-pot, and Efficient Synthesis of Betti Bases Promoted by FeCl3•6H2O

BACKGROUND

Betti bases are pharmaceutically and synthetically important scaffolds due to their diverse range of biological activities and applications in key synthetic transformations in organic synthesis.

OBJECTIVE

This work has been sought to contribute to the development, design, and implementation of an improved green methodology with higher atom economy and lower E-factor values for the synthesis of Betti bases.

METHOD

To realize our objectives, we screened out different catalysts and reaction conditions using one-pot multicomponent modified Mannich reaction/Betti reaction by employing 2-naphthol, benzaldehyde and pyrrolidine as model substrates.

RESULTS

The developed methodology afforded functionalized Betti bases via FeCl3•6H2O catalyzed one-pot multicomponent Betti reaction under neat conditions at 110 °C (5-15 min) to afford functionalized Betti bases by using several aromatic aldehydes and secondary amines in 60-100% yields.

CONCLUSION

A facile synthetic methodology with higher atom economy and lower E-factor values to synthesize Betti bases via FeCl3•6H2O catalyzed one-pot multicomponent Betti reaction of 2-naphthol, aromatic aldehydes, and secondary amines under neat conditions at 110 °C has been reported. The developed methodology offers various advantages such as excellent yields (60-100%), short reaction time (5-15 min), wide substrate scope (12 examples), green reaction conditions, readily available catalyst, and easy purification (without column chromatography).

Combining bio- and organocatalysis for the synthesis of piperidine alkaloids

There is continued interest in developing cascade processes for the synthesis of key chiral building blocks and bioactive natural products (or analogues). Here, we report a hybrid bio-organocatalytic cascade for the synthesis of a small panel of 2-substituted piperidines, relying on a transaminase to generate a key reactive intermediate for the complexity building Mannich reaction.

Recent Development of Bis-Cyclometalated Chiral-at-Iridium and Rhodium Complexes for Asymmetric Catalysis

The field of asymmetric catalysis has been developing to access synthetically efficacious chiral molecules from the last century. Although there are many sustainable ways to produce nonracemic molecules, simplified and unique methodologies are always appreciated. In the recent developments of asymmetric catalysis, chiral-at-metal Lewis acid catalysis has been recognized as an attractive strategy. The catalysts coordinatively activate a substrate while serving the sole source of chirality by virtue of its helical environment. These configurationally stable complexes were utilized in a large number of asymmetric transformations, ranging from asymmetric Lewis acid catalysis to photoredox and electrocatalysis. Here we provide a comprehensive review of the current advancements in asymmetric catalysis utilizing iridium and rhodium-based chiral-at-metal complexes as catalysts. First, the asymmetric transformations via LUMO and HOMO activation assisted by a chiral Lewis acid catalyst are reviewed. In the second part, visible-light-induced asymmetric catalysis is summarized. The asymmetric transformation via the electricity-driven method is discussed in the final section.

Synthesis and In Vitro Evaluation of C-7 and C-8 Luteolin Derivatives as Influenza Endonuclease Inhibitors

The part of the influenza polymerase PA subunit featuring endonuclease activity is a target for anti-influenza therapies, including the FDA-approved drug Xofluza. A general feature of endonuclease inhibitors is their ability to chelate Mg²⁺ or Mn²⁺ ions located in the enzyme’s catalytic site. Previously, we screened a panel of flavonoids for PA inhibition and found luteolin and its C-glucoside orientin to be potent inhibitors. Through structural analysis, we identified the presence of a 3′,4′-dihydroxyphenyl moiety as a crucial feature for sub-micromolar inhibitory activity. Here, we report results from a subsequent investigation exploring structural changes at the C-7 and C-8 positions of luteolin. Experimental IC₅₀ values were determined by AlphaScreen technology. The most potent inhibitors were C-8 derivatives with inhibitory potencies comparable to that of luteolin. Bio-isosteric replacement of the C-7 hydroxyl moiety of luteolin led to a series of compounds with one-order-of-magnitude-lower inhibitory potencies. Using X-ray crystallography, we solved structures of the wild-type PA-N-terminal domain and its I38T mutant in complex with orientin at 1.9 Å and 2.2 Å resolution, respectively.

Catalytic stereoselective Mannich-type reactions for construction of fluorinated compounds

For its unique role in developing and designing new bioactive materials and healthcare products, fluoro-organic compounds have attracted remarkable interest. Along with ever-increasing demand for a wider availability of fluorine-containing structural units, a large diversity of methods has been introduced to incorporate fluorine atoms specially in a stereoselective fashion. Among them, catalytic Mannich reaction can proceed with a broad variety of reactants and open clear paths for the synthesis of versatile amine synthons in the synthesis of natural product and pharmaceutical molecules. This review provides an overview of the employment of catalytic asymmetric Mannich reactions in the synthesis of fluorine-containing amine compounds and highlights the conceivable distinct mechanisms.

Multicomponent reactions as a potent tool for the synthesis of benzodiazepines

Benzodiazepines (BZDs), a diverse class of benzofused seven-membered N-heterocycles, display essential pharmacological properties and play vital roles in some biochemical processes. They have mainly been prescribed as potential therapeutic agents, which interestingly represent various biological activities such as anticancer, anxiolytic, antipsychotic, anticonvulsant, antituberculosis, muscle relaxant, and antimicrobial activities. The extensive biological activities of BZDs in various fields have encouraged medicinal chemists to discover and design novel BZD-based scaffolds as potential therapeutic candidates with the favorite biological activity through an efficient protocol. Although certainly valuable and important, conventional synthetic routes to these bicyclic benzene compounds contain methodologies often requiring multistep procedures, which suffer from waste materials generation and lack of sustainability. By contrast, multicomponent reactions (MCRs) have recently advanced as a green synthetic strategy for synthesizing BZDs with the desired scope. In this regard, MCRs, especially Ugi and Ugi-type reactions, efficiently and conveniently supply various complex synthons, which can easily be converted to the BZDs via suitable post-transformations. Also, MCRs, especially Mannich-type reactions, provide speedy and economic approaches for the one-pot and one-step synthesis of BZDs. As a result, various functionalized-BZDs have been achieved by developing mild, efficient, and high-yielding MCR protocols. This review covers all aspects of the synthesis of BZDs with a particular focus on the MCRs as well as the mechanism chemistry of synthetic protocols. The present manuscript opens a new avenue for organic, medicinal, and industrial chemists to design safe, environmentally benign, and economical methods for the synthesis of new and known BZDs.

Aminoalkylated Phenolic Chalcones: Investigation of Biological Effects on Acetylcholinesterase and Carbonic Anhydrase I and II as Potential Lead Enzyme Inhibitors

Background:

Phenolic Mannich bases have been reported as acetylcholinesterase (AChE) inhibitors for the medication of Alzheimer's disease. Carbonic Anhydrases (CAs) are molecular targets for anticonvulsant, diuretic and antiglaucoma drugs in the clinic. Phenolic compounds have also been mentioned as CA inhibitors. The importance of Mannich bases in drug design inspired our research group to design novel phenolic Mannic bases as potent enzyme inhibitors.

Objective:

In this study, novel Mannich bases, 1-(3,5-bis-aminomethyl-4-hydroxyphenyl)-3-(4- substitutedphenyl)-2-propen-1-ones (1-9), were designed to discover new and potent AChE inhibitors for the treatment of Alzheimer's disease and also to report their carbonic anhydrase inhibitory potency against the most studied hCA I and hCA II isoenzymes with the hope to find out promising enzyme inhibitors.

Methods:

Mannich bases were synthesized by the Mannich reaction. The structures of the compounds were elucidated by 1H NMR, 13C NMR, and HRMS. Enzyme inhibitory potency of the compounds was evaluated spectrophotometrically towards AChE, hCA I and hCA II enzymes.

Results and Discussion:

The compounds showed inhibition potency in nanomolar concentrations against AChE with Ki values ranging from 20.44±3.17 nM to 43.25±6.28 nM. They also showed CAs inhibition potency with Ki values in the range of 11.76±1.29-31.09±2.7 nM (hCA I) and 6.08 ± 1.18-23.12±4.26 nM (hCA II). Compounds 1 (hCA I), 5 (hCA II), and 4 (AChE) showed significant inhibitory potency against the enzymes targeted.

Conclusion:

Enzyme assays showed that Mannich derivatives might be considered as lead enzyme inhibitors to design more selective and potent compounds targeting enzyme-based diseases.

Hf(OTf)4 as a Highly Potent Catalyst for the Synthesis of Mannich Bases under Solvent-Free Conditions

Hf(OTf)4 was identified as a highly potent catalyst (0.1-0.5 mol%) for three-component Mannich reaction under solvent-free conditions. Hf(OTf)4-catalyzed Mannich reaction exhibited excellent regioselectivity and diastereoselectivity when alkyl ketones were employed as substrates. 1H NMR tracing of the H/D exchange reaction of ketones in MeOH-d4 indicated that Hf(OTf)4 could significantly promote the keto-enol tautomerization, thereby contributing to the acceleration of reaction rate.

Two-stage one-pot synthesis of N-(dibutylaminomethyl)methacrylamide by Mannich reaction under mild conditions with high yield

N-(Dibutylaminomethyl)methacrylamide can be easily obtained via a two-stage one-pot Mannich reaction under mild conditions. By-products are practically absent and the monomer can be easily isolated from the reaction mixture with a 96% yield.

Synthesis of Novel 8-Hydroxyquinoline Derivatives through Mannich Reaction and their Biological Evaluation as Potential Immunomodulatory Agents

BACKGROUND

In continuation of our work on Mannich reaction on 8-hydroxyquinoline, fifteen different combinations of aromatic aldehydes and aniline were subjected to Mannich reaction from which twelve products (eight Mannich bases, two imines and two intramolecularly cyclized products with benzofuranone skeleton) were obtained. Among them six compounds (1, 2, 6, 8, 9 and 12) are the new compounds. The structures of the compounds were characterized by UV, IR, MS and 1H NMR.

METHODS

The compounds were tested for the inhibition of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and Interleukin-1β (IL-1β) at a concentration of 25 µg/mL. The cytokines were produced by THP-1 cells differentiated with PMA for 24hrs and stimulated with LPS for 4 hrs and supernatant were analyzed through ELISA technique.

RESULTS AND DISCUSSION

Compounds 1-5, 8 and 9 inhibited the production of TNF-α and IL-1β. Compounds 1, 3, and 8 exerted potent inhibitions of TNF-α with 71%, 71%, and 83% inhibition, respectively. Compounds 1 and 8 significantly inhibited the production of IL-1β with 64% and 78% inhibition, respectively.

CONCLUSION

Compounds 1 and 8 significantly inhibited the production of IL-1β with 64% and 78% inhibition, respectively. Notably compound 8 showed the most potent inhibition of these cytokines. Additionally, the effect of compounds on viability of THP-1 cells was also evaluated. Moreover, molecular docking was carried out to study the mechanism of inhibition of TNF-α production.

Acetophenone Mannich bases: study of ionic liquid catalysed synthesis and antioxidative potential of products

Three-component Mannich reaction of acetophenone or 4-iodoacetophenone with a variety of substituted anilines and benzaldehyde, catalysed with diethanolammonium chloroacetate, was performed under mild conditions. Mannich bases (MBs), of which five are new, were obtained in good to excellent yields. All compounds were characterized using elemental analysis, NMR and IR. In addition, detailed experimental and simulated UV-Vis spectral characterization of these compounds is presented here for the first time. In vitro antioxidative potential of synthetized MBs was evaluated using 2,2-diphenyl-1-picryl-hydrazyl radical and density functional theory (DFT) thermodynamical study. It was shown that compounds with anisidine moiety express moderate antioxidative activity. Mechanism of the organocatalysed Mannich reaction was thoroughly inspected by means of DFT. The reaction undergoes the hydrogen bonding-assisted mechanism. Moreover, the proposed rate determining step of the overall reaction is water elimination in the process of iminium ion formation. To the extent of our knowledge, this is the first detailed report on the influence of this type of catalyst on the formation of iminium ion, as a crucial intermediate for the whole reaction.

Modified tannins and their application in wastewater treatment

The bio-flocculants used in this study were synthesised by the Mannich reaction, which includes three reagents: a substrate (tannin extracts of Acacia, Quebracho, and Castanea), formaldehyde, and an amine derivative (ethanolamine, diethanolamine, ammonium chloride). Nine natural flocculants were prepared by combining extracts and amines; these products were evaluated in three different wastewater samples in two experimental phases. In phase I, five physicochemical parameters were analysed. From the data obtained, a multivariate, completely randomised design (CRD-Manava) was used, with a factorial arrangement and mean plots. In phase II, the three bio-flocculants with the most statistically significant responses and their mixtures were examined, evaluating 14 biological and physicochemical parameters. Statistical analysis was guided in this phase by CRD blocks, finding a significant removal in the physicochemical parameters analysed in the different types of wastewater and obtaining removal rates between 50 and 90%, depending on the parameter. At the end of both phases, the bio-flocculants acacia-ammonium chloride and quebracho-diethanolamine were the most efficient in the removal of turbidity (34-99%), true colour (93-100%) and total solids (12-99%). In addition, the natural flocculants showed low mutagenicity index (MI: 0.33-0.93) compared to aluminium sulphate (MI: 4.87-8.81).

Synthesis, biological evaluation and molecular dynamics studies of 1,2,4-triazole clubbed Mannich bases

The present work highlightsthe synthesis of a newer biologically active Mannich bases contributing 4-((4-fluorobenzylidene)amino)-5-(pyridin-4-yl)-4H-1,2,4-triazole-3-thiol and various heterocyclic amines via N-Mannich reaction by the conventional method as well as microwave heating approach as a part of an environmentally benign synthetic protocol. All the synthesized compounds were characterized by spectral analysis and were screened for in vitro antimicrobial, antitubercular and antiprotozoal activity. The compound 4k was found to be most active respectively against S. aureus (MIC 12.5 μM) and C. albicans (MIC 100 μM). The derivative 4 g displayed potency against L.mexicana and T. cruzi with IC₅₀ value 1.01 and 3.33 μM better than reference drug Miltefosina and Nifurtimox. The compound 4b displayed excellent potency against M. tuberculosis (MIC 6.25 μM) in the primary screening. The computational studies revealed for that Mannich derivative (4b) showed a high affinity toward the active site of enzyme which provides a strong platform for new structure-based design efforts. The Lipinski's parameters showed good drug-likeness properties and can be developed as an oral drug candidate.