Michael-type Addition Research Articles

Enantioselective Assembly of Fully Substituted α-Amino Allenoates Through a Mannich Addition and Stepwise [3,3]-σ Rearrangement Sequence.

Chiral fully-substituted allenes are synthetically significant and pivotal building blocks that can engage in diverse transformations toward a variety of bioactive molecules. The enantioselective assembly of these skeletons using readily available reactants offers significant advantages but remains challenging. Herein, an asymmetric formal Michael-type addition of alkynyl imines with the key alkylgold intermediates derived in situ from N-propargylamides is accomplished under gold-complex and chiral quinine-derived squaramide (QN-SQA) synergetic catalysis. Control experiments and the density functional theory (DFT) calculations indicated that this cascade reaction involves a Mannich-type addition and stepwise [3,3]-σ rearrangement sequence, leading to the fully substituted α-amino allenoates, which are elusive and take multi-step to prepare with other methods, in high yields and excellent enantioselectivity.

Bacteria encapsulation into polyethylene glycol hydrogels using Michael-type addition reactions

AbstractHydrogel materials can be used to integrate bacteria cells into biohybrid systems. Here, we investigate the use of polyethylene glycol-based hydrogels that employ different Michael-type addition crosslinking chemistries, including thiol-acrylate, thiol-vinyl sulfone, and thiol-maleimide click reactions, for covalent hydrogel network formation and bacteria encapsulation. All crosslinking chemistries generated hydrogels that provided stable encapsulation and culture of Bacillus subtilis; however, significant differences in cell viability and cell morphology after encapsulation were identified. Thiol-acrylate hydrogels provided the highest cell viability and favored encapsulation of single cells, while thiol-maleimide hydrogels had the lowest cell viability and favored encapsulation of larger aggregates. These findings demonstrate the impact of crosslinking strategies for encapsulation of microorganisms into hydrogel networks and suggest that thiol-acrylate chemistries are favorable for many applications. Graphical abstract

Curved Nanographenes as Stoppers in a [2]Rotaxane with Two-Photon Excited Emission.

Heptagon-containing distorted nanographenes are used as stoppers for the capping of a [2]rotaxane through a Michael-type addition reaction to vinyl sulfone groups. These curved aromatics are bulky enough to prevent the disassembly of the rotaxane but also give emissive and nonlinear (two-photon absorption and emission) optical properties to the structure.

Surface decoration of PLGA nanoparticles enables efficient transport of floxuridine oligomers into mammalian cells

2′-deoxy-5-fluorouridine (Floxuridine, FdU) oligomers are repeated FdU residues linked to each other through phosphate groups exhibiting anticancer properties. One of the major hurdles exhibited by natural oligomers is their reduced stability and limited ability to impart cellular uptake. To overcome these drawbacks, electrostatic and covalent strategies have been used to combine oligomers with nanoparticles (NPs) to enhance stability and cellular internalization. Polymeric NPs, prepared from oil-in-water (O/W) PLGA nano-emulsions (NEs) using low-energy emulsification methods, have shown potential in many biomedical applications owing to their ability to transport drugs across cellular membranes. Carbodiimide-mediated amine coupling reaction and thiol-based Michael-type addition were used to attach FdU oligomers formed by five FdU residues (FdU5) to PLGA NPs. Colloidally stable dispersions of FdU5-decorated PLGA NPs were obtained and characterized in terms of size, surface charge, and morphology in physiological medium. Additionally, synthetic strategies were envisaged to functionalize the surface of FdU5-decorated polymeric NPs with folic acid (FA). Cell culture experiments showed that FdU5-decorated PLGA NPs were able to internalize efficiently inducing cytotoxic effect and inhibiting cell proliferation in tumor cells. These outcomes suggest the feasibility of grafting oligomeric FdU produgs in a covalent fashion into nanoscale platforms as a potential approach for cancer therapy.

Fluorine-Free Single-Component Polyelectrolyte of Poly(ethylene glycol) Bearing Lithium Methanesulfonylsulfonimide Terminal Groups: Effect of Structural Variance on Ionic Conductivity

Fluorine-free single-component polyelectrolytes were developed via the hybridization of lithium methanesulfonylsulfonimide (LiMSSI) moieties to poly(ethylene glycol) (PEG) derivatives with different morphologies, and the relationship between the structure and its ionic conductivity was investigated. The PEG-LiMSSI derivatives with one, two, and three LiMSSI end groups were prepared via the concomitant Michael-type addition and lithiation of PEGs and N-methanesulfonylvinylsulfonimide. The ionic conductivity at 60 °C ranged from 1.8 × 10−7 to 2.0 × 10−4 S/cm. PEG-LiMSSI derivatives with one LiMSSI terminus and with two LiMSSI termini at both ends show higher ionic conductivity, that is as good as fluorine-free single-component polyelectrolytes, than that with two LiMSSI termini at one end and that with three LiMSSI termini.

Design, synthesis and anti-tumor evaluation of novel thiohydantoin congeners as androgen receptor antagonists with in vivo study

Novel thiohydantoin derivatives were designed as androgen antagonists based on the binding pattern of enzalutamide to the androgen receptor that avoided the bifurcated activation pattern of dihydrotestosterone. Twelve thiohydantoin derivatives were synthesized following Michael-type addition which were fully characterized. The dicyanide derivatives 3a showed the best LNCaP inhibition demonstrating IC50 of 2.64 µM with a potential to inhibit its S-phase reducing the natural DNA transactivation of androgens. Moreover, apoptosis initiation was observed in the early phase with 22.74 % in contrast to 9.06 % at the late phase with respect to 0.44 % and 0.13 % of the control cells at early and late stages, respectively. In vivo evaluation of 3a significantly ameliorated the testosterone-induced increase in the prostate index and weight as compared to finasteride. This was confirmed by the histopathological examinations of prostatic tissues that demonstrated a reduction in the accompanied histopathological changes as well as lowering the immunohistochemical up-regulation of androgen receptors induced by testosterone. Moreover, molecular docking simulation justified the achieved biological activity.

Synthesis of obovatol and related neolignan analogues as α-glucosidase and α-amylase inhibitors

Diabetes mellitus is a metabolic disease characterized by hyperglycemia, which can be counteracted by the inhibition of α-glucosidase (α-Glu) and α-amylase (α-Amy), enzymes responsible for the hydrolysis of carbohydrates. In recent decades, many natural compounds and their bioinspired analogues have been studied as α-Glu and α-Amy inhibitors. However, no studies have been devoted to the evaluation of α-Glu and α-Amy inhibition by the neolignan obovatol (1). In this work, we report the synthesis of 1 and a library of new analogues. The synthesis of these compounds was achieved by implementing methodologies based on: phenol allylation, Claisen/Cope rearrangements, methylation, Ullmann coupling, demethylation, phenol oxidation and Michael-type addition. Obovatol (1) and ten analogues were evaluated for their in vitro inhibitory activity towards α-Glu and α-Amy. Our investigation highlighted that the naturally occurring 1 and four neolignan analogues (11, 22, 26 and 27) were more effective inhibitors than the hypoglycemic drug acarbose (α-Amy: 34.6 µM; α-Glu: 248.3 µM) with IC5O value of 6.2–23.6 µM toward α-Amy and 39.8–124.6 µM toward α-Glu. Docking investigations validated the inhibition outcomes, highlighting optimal compatibility between synthesized neolignans and both the enzymes. Concurrently circular dichroism spectroscopy detected the conformational changes in α-Glu induced by its interaction with the studied neolignans. Detailed studies through fluorescence measurements and kinetics of α-Glu and α-Amy inhibition also indicated that 1, 11, 22, 26 and 27 have the greatest affinity for α-Glu and 1, 11 and 27 for α-Amy. Surface plasmon resonance imaging (SPRI) measurements confirmed that among the compounds studied, the neolignan 27 has the greater affinity for both enzymes, thus corroborating the results obtained by kinetics and fluorescence quenching. Finally, in vitro cytotoxicity of the investigated compounds was tested on human colon cancer cell line (HCT-116). All these results demonstrate that these obovatol-based neolignan analogues constitute promising candidates in the pursuit of developing novel hypoglycemic drugs.

A Versatile Thioesterase Involved in Dimerization during Cinnamoyl Lipid Biosynthesis.

The cinnamoyl lipid compound youssoufene A1 (1), featuring a unique dearomatic carbon-bridged dimeric skeleton, exhibits increased inhibition against multidrug resistant Enterococcus faecalis as compared to monomeric youssoufenes. However, the formation process of this intriguing dearomatization/dimerization remains unknown. In this study, an unusual "gene-within-gene" thioesterase (TE) gene ysfF was functionally characterized. The gene was found to naturally encodes two proteins, an entire YsfF with α/β-hydrolase and 4-hydroxybenzoyl-CoA thioesterase (4-HBT)-like enzyme domains, and a nested YsfFHBT (4-HBT-like enzyme). Using an intracellular tagged carrier-protein tracking (ITCT) strategy, in vitro reconstitution and in vivo experiments, we found that: i) both domains of YsfF displayed thioesterase activities; ii) YsfF/YsfFHBT could accomplish the 6π-electrocyclic ring closure for benzene ring formation; and iii) YsfF and cyclase YsfX together were responsible for the ACP-tethered dearomatization/dimerization process, possibly through an unprecedented Michael-type addition reaction. Moreover, site-directed mutagenesis experiments demonstrated that N301, E483 and H566 of YsfF are critical residues for both the 6π-electrocyclization and dimerization processes. This study enhances our understanding of the multifunctionality of the TE protein family.

A tough and bioadhesive injectable hydrogel formed with maleimidyl alginate and pristine gelatin

Injectable hydrogels have wide applications in clinical practice. However, the development of tough and bioadhesive ones based on biopolymers, along with biofriendly and robust crosslinking strategies, still represents a great challenge. Herein, we report an injectable hydrogel composed of maleimidyl alginate and pristine gelatin, for which the precursor solutions could self-crosslink via mild Michael-type addition without any catalyst or external energy upon mixing. This hydrogel is tough and bioadhesive, which can maintain intactness as well as adherence to the defect of porcine skin under fierce bending and twisting, warm water bath, and boiling water shower. Besides, it is biocompatible, bioactive and biodegradable, which could support the growth and remodeling of cells by affording an extracellular matrix-like environment. As a proof of application, we demonstrate that this hydrogel could significantly accelerate diabetic skin wound healing, thereby holding great potential in healthcare.

Enhancing Mucoadhesive Properties of Gelatin through Chemical Modification with Unsaturated Anhydrides.

Gelatin is a water-soluble natural polyampholyte with poor mucoadhesive properties. It has traditionally been used as a major ingredient in many pharmaceuticals, including soft and hard capsules, suppositories, tissue engineering, and regenerative medicine. The mucoadhesive properties of gelatin can be improved by modifying it through conjugation with specific adhesive unsaturated groups. In this study, gelatin was modified by reacting with crotonic, itaconic, and methacrylic anhydrides in varying molar ratios to yield crotonoylated-, itaconoylated-, and methacryloylated gelatins (abbreviated as Gel-CA, Gel-IA, and Gel-MA, respectively). The successful synthesis was confirmed using 1H NMR, FTIR spectroscopies, and colorimetric TNBSA assay. The effect of chemical modification on the isoelectric point was studied through viscosity and electrophoretic mobility measurements. The evolution of the storage (G') and loss (G'') moduli was employed to determine thermoreversible gelation points of modified and unmodified gelatins. The safety of modified gelatin derivatives was assessed with an in vivo slug mucosal irritation test (SMIT) and an in vitro MTT assay utilizing human pulmonary fibroblasts cell line. Two different model dosage forms, such as physical gels and spray-dried microparticles, were prepared and their mucoadhesive properties were evaluated using a flow-through technique with fluorescent detection and a tensile test with ex vivo porcine vaginal tissues and sheep nasal mucosa. Gelatins modified with unsaturated groups exhibited superior mucoadhesive properties compared to native gelatin. The enhanced ability of gelatin modified with these unsaturated functional groups is due to the formation of covalent bonds with cysteine-rich subdomains present in the mucin via thiol-ene click Michael-type addition reactions occurring under physiologically relevant conditions.

Phosphine Catalyzed Michael-Type Additions: The Synthesis of Glutamic Acid Derivatives from Arylidene-α-amino Esters.

The reaction of arylidene-α-amino esters with electrophilic alkenes to yield Michael-type addition compounds is optimized using several phosphines as organocatalysts. The transformation is very complicated due to the generation of several final compounds, including those derived from the 1,3-dipolar cycloadditions. For this reason, the selection of the reaction conditions is a very complex task and the slow addition of the acrylic system is very important to complete the process. The study of the variation in the structural components of the starting imino ester is performed as well as the expansion of other electron-poor alkenes. The crude products have a purity higher than 90% in most cases without any purification. A plausible mechanism is detailed based on the bibliography and the experimental results. The synthesis of pyroglutamate entities, after the reduction of the imino group and cyclization, is performed in high yields. In addition, the hydrolysis of the imino group, under acidic media, represents a direct access to glutamate surrogates.

A fluorescent probe with serum albumin as a signal amplifier for real-time sensing of HSO3- in solution, mitochondria of animal cells and rice roots.

Endogenous release of HSO3- during the enzymatic oxidation of sulfur containing amino acids in mitochondria or insufficiency of sulfite oxidase results in the accumulation of sulfite and thiosulfate in biological fluids affecting mitochondrial homeostasis of brain mitochondria associated with serious clinical symptoms related to neurological disorders. The red fluorescent probe MGQ undergoes self-assembly in water and reveals aggregation induced quenching of fluorescence. MGQ reveals 143-fold and 179-fold increases in fluorescence intensity at 645 nm, respectively, in the presence of HSA and BSA and does not significantly differentiate between two albumins. The detailed studies of MGQ have been performed in the presence of BSA. The presence of other enzymes/proteins and amino acids, viz. pepsin, trypsin, lysozyme, Bromelain, lysine, histidine, hemoglobin, etc., does not affect the fluorescence of MGQ or MGQ-BSA solutions and points to high selectivity towards BSA. The limit of detection for BSA is 10 nM. In PBS buffer, MGQ in the absence of BSA does not react with HSO3- and sluggishly in a 1 : 1 ethanol-water mixture. However, in the confined space of BSA/HSA, MGQ displays a signal amplification, undergoes instantaneous Michael type addition of HSO3- and results in a ratiometric change in fluorescence intensity in ≤1.5 min with the decrease of red fluorescence at 645 nm and emergence of green fluorescence at 515 nm. The LOD for the detection of HSO3- is 4 nM.

Nitrogen-containing andrographolide derivatives with multidrug resistance reversal effects in cancer cells.

Multidrug resistance (MDR) remains a challenging issue in cancer treatment. Aiming at finding anticancer agents to overcome MDR, the triacetyl derivative (2) of the labdane diterpenoid lactone andrographolide (1) underwent the Michael-type addition reaction followed by elimination, yielding twenty-three new derivatives, bearing nitrogen-containing substituents (3-25). Their structures were assigned, mainly, by 1D and 2D NMR experiments. The MDR reversal potential of compounds 1-25 was assessed, by functional and chemosensitivity assays, using resistant human ABCB1-gene transfected L5178Y mouse lymphoma cells as a model. Several derivatives exhibited remarkable P-glycoprotein (P-gp) inhibitory ability. Compounds 13 and 20, bearing thiosemicarbazide moieties, were the most active exhibiting a strong MDR reversal effect at 2 μM. Some compounds showed selectivity towards the resistant cells, with compound 5 exhibiting a collateral sensitivity effect associated with significant antiproliferative activity (IC50 = 5.47 ± 0.22 μM). Moreover, all selected compounds displayed synergistic interaction with doxorubicin, with compound 3 being the most active. In the ATPase assay, selected compounds exhibited characteristics of P-gp inhibitors.

From burst to controlled release: using hydrogel crosslinking chemistry to tune release of micro-crystalline active pharmaceutical ingredients

In this study, a nanoemulsion of a BCS class II drug, fenofibrate, was cross-linked via a Michael-type addition reaction to yield micro-crystalline Fen-embedded micro-hydrogels with tunable degradation.

An ultrafast and highly sensitive fluorescent probe for the detection of HSO3− and its application in food samples and SO2 gas

SO2 is one of the main components of air pollution gas, its derivatives HSO3− and SO32− were considerable used as food additive because of their antiseptic and bacteriostatic effects. Excessive intake of HSO3− is harmful to human health, so it is extremely important to detect the content of HSO3− in food sample by effective method. In this work, a small molecular fluorescence probe TPE-O based on tetraphenylethene fluorophore was designed and synthesized. The probe showed ultrafast (< 3 s) and obvious colorimetric response to HSO3− with high selectivity and sensitivity (LOD = 210 nM). The possible Michael-type addition of HSO3− on the activated C = C bond blocked the π-conjugated system, thus lead to changes in fluorescence and absorption spectra. Probe TPE-O not only can detect the content of HSO3− in sugar and wine, but also can be loaded on agarose hydrogel to detect SO2 gas. Therefore, this work provided a powerful tool for the detection of HSO3− in food samples and SO2 gas.

A Novel Natural Siderophore Antibiotic Conjugate Reveals a Chemical Approach to Macromolecule Coupling.

Inspired by natural sideromycins, the conjugation of antibiotics to siderophores is an attractive strategy to facilitate "Trojan horse" delivery of antibiotics into bacteria. Genome analysis of a soil bacterium, Dactylosporangium fulvum, found a "hybrid" biosynthetic gene cluster responsible for the production of both an antibiotic, pyridomycin, and a novel chlorocatechol-containing siderophore named chlorodactyloferrin. While both of these natural products were synthesized independently, analysis of the culture supernatant also identified a conjugate of both molecules. We then found that the addition of ferric iron to purified chlorodactyloferrin and pyridomycin instigated their conjugation, leading to the formation of a covalent bond between the siderophore-catechol and the pyridomycin-pyridine groups. Using model reactants, this iron-based reaction was found to proceed through a Michael-type addition reaction, where ferric iron oxidizes the siderophore-catechol group into its quinone form, which is then attacked by the antibiotic pyridyl-nitrogen to form the catechol-pyridinium linkage. These findings prompted us to explore if other "cargo" molecules could be attached to chlorodactyloferrin in a similar manner, and this was indeed confirmed with a pyridine-substituted TAMRA fluorophore as well as with pyridine-substituted penicillin, rifampicin, and norfloxacin antibiotic analogues. The resultant biomimetic conjugates were demonstrated to effectively enter a number of bacteria, with TAMRA-chlorodactyloferrin conjugates causing fluorescent labeling of the bacteria, and with penicillin and rifampicin conjugates eliciting antibiotic activity. These findings open up new opportunities for the design and facile synthesis of a novel class of biomimetic siderophore conjugates with antibiotic activity.

Ni-Catalyzed Hydrosulfonylation of Alkenes with Aromatic Iodides and K2S2O5.

Hydrosulfonylation of alkenes with readily available aromatic iodides via a SO2-insetion strategy is presented. The combination of non-noble Ni catalysis with (iPr)3SiH as the final reductant enables the efficient formation of aryl and heteroaryl sulfinate intermediates, which undergo Michael-type additions to electron-deficient alkenes for initiating the hydrosulfonylation process. Moreover, the superiority of this protocol is demonstrated by broad substrate scope and good functional group compatibility.

Theoretical study of an N-heterocyclic carbene-catalyzed annulation reaction between an enal and a β-silyl enone: Mechanism and origin of stereoselectivity

In this study, the mechanism and origin of the stereoselectivity of an N-heterocyclic carbene (NHC)-catalyzed transformation reaction between an enal and a β-silyl enone are systematically investigated using density functional theory (DFT) at the M06-2X level. Multiple pathways are proposed and studied to identify the most energetically favorable mechanism for the reaction. The calculation results show that the most energetically favorable pathway comprises the following processes: nucleophilic addition of NHC to the Si-face of the enal to form a zwitterionic intermediate, two sequential CsHCO3-assisted intramolecular proton shifts to produce an enolate intermediate, Michael-type addition of the enolate intermediate to the β-silyl enone, ring closure to construct a six-membered ring intermediate, and the dissociation of NHC to release the final product. The reaction between the enolate intermediate and the β-silyl enone is identified as the stereoselectivity-determining step, preferentially generating an RS-configured product. Subsequent atoms-in-molecules (AIM) and noncovalent interaction (NCI) analyses verify that the main factor for inducing stereoselectivity is the higher number of noncovalent intermolecular interactions in the low-energy transition state.

Enantioselective Addition of Dialkyl Malonates to β-Arylethenesulfonyl Fluorides under High-Pressure Conditions.

Application of high-pressure conditions enables enantioselective Michael-type addition of dialkyl malonates to β-arylethenesulfonyl fluorides. The reaction is efficiently catalyzed with 5 mol % of tertiary amino-thiourea at 9 kbar. Chiral alkanesulfonyl fluorides are formed in yields of up to 96% and enantioselectivities of up to 92%. Functionalization of the adducts via sulfur fluoride exchange (SuFEx) reaction and desulfonylative cyclization is demonstrated.

In Situ Cross-Linkable Hyaluronic-Ferulic Acid Conjugate Containing Bucladesine Nanoparticles Promotes Neural Regeneration after Spinal Cord Injury.

Dysfunctional clinical outcomes following spinal cord injury (SCI) result from glial scar formation, leading to the inhibition of new axon growth and impaired regeneration. Nevertheless, nerve regeneration after SCI is possible, provided that the state of neuron development in the injured environment is improved. Hence, biomaterial-based therapy would be a promising strategy to endow a desirable environment for tissue repair. Herein, we designed a novel multifunctional injectable hydrogel with antioxidant, neuroprotective, and neuroregenerative effects. Bucladesine-encapsulated chitosan nanoparticles (BCS NPs) were first prepared and embedded in a matrix of thiol-functionalized hyaluronic acid modified with ferulic acid (HASH-FA). The target hydrogel (HSP-F/BCS) was then created through Michael-type addition between HASH-FA containing BCS NPs and four-arm polyethylene glycol-maleimide (4-Arm-PEG-Mal). The obtained hydrogel with shear thinning behavior showed viscoelastic and mechanical properties similar to the normal nerve tissue. FA conjugation significantly improved the antioxidant activity of HA, and suppressed intracellular ROS formation. In situ injection of the HSP-F/BCS hydrogel in a rat contusion model of SCI inhibited glial scar progression, reduced microglia/macrophage infiltration, promoted angiogenesis, and induced myelinated axon regeneration. As a result, a significant improvement in motor performance was observed compared to other experimental groups. Taken together, the HSP-F/BCS hydrogel developed in this study could be a promising system for SCI repair.