Conjugate addition of amino acid side chains to alkynones and alkynoic acid derivatives

Phenylpropynones as Selective Disulfide Rebridging Bioconjugation Reagents

Simple 1-phenylpropynones undergo a selective double thia-Michael addition with thiols in buffered media, yielding an interesting dithioacetal linkage joining two thiols. The reactivity of various Michael-alkyne reagents is compared in this chemoselective, atom economical, and non-oxidative cross-linking of two thiols. The stability and chemical reactivity of the dithioacetal links are studied, and the utility of the disulfide targeting bioconjugation methodology is shown by the selective rebridging of native cyclic peptides after the reductive cleavage of their disulfide bridge.

Chalcones: Promising therapeutic agents targeting key players and signaling pathways regulating the hallmarks of cancer

The need for innovative anticancer treatments with high effectiveness and low toxicity is urgent due to the development of malignancies that are resistant to chemotherapeutic agents and the poor specificity of existing anticancer treatments. Chalcones are 1,3-diaryl-2-propen-1-ones, which are the precursors for flavonoids and isoflavonoids. Chalcones are readily available from a wide range of natural resources and consist of very basic chemical scaffolds. Because the ease with which the synthesis it allows for the production of several chalcone derivatives. Various in-vitro and in-vivo studies indicate that naturally occurring and synthetic chalcone derivatives exhibit promising biological activities against cancer hallmarks such as proliferation, angiogenesis, invasion, metastasis, inflammation, stemness, and regulation of cancer epigenetics. According to their structure and functional groups, chalcones derivatives and their hybrid compounds exert a broad range of biological activities through targeting key elements and signaling molecules relevant to cancer progression. This review will provide valuable insights into the latest updates of chalcone groups as anticancer agents and extensively discuss their underlying molecular mechanisms of action.

Click Step-Growth Polymerization and E/Z Stereochemistry Using Nucleophilic Thiol-yne/-ene Reactions: Applying Old Concepts for Practical Sustainable (Bio)Materials

Polymer sustainability is synonymous with "bioderived polymers" and the zeitgeist of "using renewable feedstocks". However, this sentiment does not adequately encompass the requirements of sustainability in polymers. In addition to recycling considerations and mechanical performance, following green chemistry principles also needs to be maximized to improve the sustainability of polymer synthesis. The synthetic cost (i.e., maximizing atom economy, reducing chemical hazards, and lowering energy requirements) of producing polymers should be viewed as equally important to the monomer source (biomass vs petrol platform chemicals). Therefore, combining the use of renewable feedstocks with efficient syntheses and green chemistry principles is imperative to delivering truly sustainable polymers. The high efficiency, atom economy, and single reaction trajectories that define click chemistry reactions position them as ideal chemical approaches to synthesize polymers in a sustainable manner while simultaneously expanding the structural scope of accessible polymers from sustainably sourced chemicals.Click step-growth polymerization using the thiol-yne Michael addition, a reaction first reported over a century ago, has emerged as an extremely mild and atom-efficient pathway to yield high-performance polymers with controllable E/Z stereochemistry along the polymer backbone. Building on studies of aromatic thiol-yne polymers, around 10 years ago our group began investigating the thiol-yne reaction for the stereocontrolled synthesis of alkene-containing aliphatic polyesters. Our early studies established a convenient path to high-molecular-weight (>100 kDa) E-rich or Z-rich step-growth polymers by judiciously changing the catalyst and/or reaction solvent. This method has since been adapted to synthesize fast-degrading polyesters, high-performance polyamides, and resilient hydrogel biomaterials. Across several systems, we have observed dramatic differences in material properties among polymers with different alkene stereochemistry.We have also explored the analogous thiol-ene Michael reaction to create high-performance poly(ester-urethanes) with precise E/Z stereochemistry. In contrast to the stereoselective thiol-yne polymerization, here the use of monomers with predefined E/Z (geometric) isomerism (arising from either alkenes or the planar rigidity of ring units) affords polymers with total control over stereochemistry. This advancement has enabled the synthesis of tough, degradable materials that are derived from sustainable monomer feedstocks. Employing isomers of sugar-derived isohexides, bicyclic rigid-rings possessing geometric isomerism, led to degradable polymers with fundamentally opposing mechanical behavior (i.e., plastic vs elastic) simply by adjusting the stereochemistry of the isohexide.In this Account, we feature our investigation of thiol-yne/-ene click step-growth polymers and efforts to establish structure-property relationships toward degradable materials with practical mechanical performance in the context of sustainable polymers and/or biomaterials. We have paid attention to installing and controlling geometric isomerism by using these click reactions, an overarching objective of our work in this research area. The exquisite control of geometric isomerism that is possible within polymer backbones, as enabled by convenient click chemistry reactions, showcases a powerful approach to creating multipurpose degradable polymers.

Identification of Potential Drug Targets of Broad-Spectrum Inhibitors with a Michael Acceptor Moiety Using Shotgun Proteomics

The Michael addition reaction is a spontaneous and quick chemical reaction that is widely applied in various fields. This reaction is performed by conjugating an addition of nucleophiles with α, β-unsaturated carbonyl compounds, resulting in the bond formation of C-N, C-S, C-O, and so on. In the development of molecular materials, the Michael addition is not only used to synthesize chemical compounds but is also involved in the mechanism of drug action. Several covalent drugs that bond via Michael addition are regarded as anticarcinogens and anti-inflammatory drugs. Although drug development is mainly focused on pharmaceutical drug discovery, target-based discovery can provide a different perspective for drug usage. However, considerable time and labor are required to define a molecular target through molecular biological experiments. In this review, we systematically examine the chemical structures of current FDA-approved antiviral drugs for potential Michael addition moieties with α, β-unsaturated carbonyl groups, which may exert an unidentified broad-spectrum inhibitory mechanism to target viral or host factors. We thus propose that profiling the targets of antiviral agents, such as Michael addition products, can be achieved by employing a high-throughput LC-MS approach to comprehensively analyze the interaction between drugs and targets, and the subsequent drug responses in the cellular environment to facilitate drug repurposing and/or identify potential adverse effects, with a particular emphasis on the pros and cons of this shotgun proteomic approach.

Sulfuroxygen interaction-controlled (Z)-selective anti-Markovnikov vinyl sulfides

The sulfur oxygen (SO) interaction was used herein to obtain (Z)-selective anti-Markovnikov vinyl sulfides from the addition of thiyl radicals to terminal alkynes. DFT calculations predicted that SO interaction originated from the delocalization of the lone-pair of the carbonyl oxygen to the adjacent σ* orbital of the S atom of C-S.

Thiol-yne click reaction: an interesting way to derive thiol-provided catechols

The hydrothiolation of activated alkynes is presented as an attractive and powerful way to functionalize thiols bearing catechols. The reaction was promoted by a heterogeneous catalyst composed of copper nanoparticles supported on TiO₂ (CuNPs/TiO₂) in 1,2-dichloroethane (1,2-DCE) under heating at 80 °C. The catalyst could be recovered and reused in three consecutive cycles, showing a slight decrease in its catalytic activity. Thiol derivatives bearing catechol moieties, obtained through a versatile Michael addition, were reacted with different activated alkynes, such as methyl propiolate, propiolic acid, propiolamide or 2-ethynylpyridine. The reaction was shown to be regio- and stereoselective towards anti-Markovnikov Z-vinyl sulfide in most cases studied. Finally, some catechol derivatives obtained were tested as ligands in the preparation of coordination polymer nanoparticles (CNPs), by taking the advantage of their different coordination sites with metals such as iron and cobalt.

An attractive approach to the synthesis of catechol derivates through thiol-yne click reaction is presented. Compounds obtained were used in the preparation of CNPs.

Michael Addition/S,N-Intramolecular Rearrangement Sequence Enables Selective Fluorescence Detection of Cysteine and Homocysteine

Acrylate has been widely used as the recognition unit for Cys fluorescent probes. Despite this widespread use, a potential drawback of this probe type is that the ester linkage between the fluorophore and acryloyl recognition unit is liable to be hydrolyzed by abundant esterase in the cytosol, thus affording a high background signal. To solve this problem, we herein put forward a new strategy to construct a selective fluorescent probe for cysteine (Cys)/homocysteine (Hcy) with propynamide as the recognition moiety. The free probe CPA displays weakly fluorescent emission in aqueous media because of the donor-excited photoinduced electron transfer (d-PET) process within the molecule. The Michael addition of Cys (or Hcy) thiols to the conjugated alkyne of CPA gives the expected β-sulfido-α,β-unsaturated amides (1a/1b), which subsequently undergo an intramolecular S,N rearrangement, yielding β-amino-α,β-unsaturated amides (2a/2b) as the final products. The above cascade reaction results in the blockage of d-PET within CPA, thus affording a dramatic fluorescence enhancement at 495 nm. The involvement of the sulfhydryl and the adjacent amino groups in the sensing process renders CPA high selectivity for Cys/Hcy over glutathione as well as other amino acids. The probe has been successfully applied to image Cys in different cell lines. Further, CPA shows two-photon fluorescence properties, and its ability to monitor Cys in deep tissues has been demonstrated by using two-photon microscopy.

Diastereoselective alkylations of a protected cysteinesulfenate

To further understand stereoselection in the alkylation of sulfenate anions, a protected cysteinesulfenate was generated in THF solution at low temperature. Introduction of a reactive alkylating agent brings about a cysteinyl sulfoxide in 51-75% yield, with diastereomeric ratios at the sulfinyl group ranging from 83:17 to 95:5. An internally complexed lithium counterion is proposed to account for the stereoselectivity.

A new protocol for the consecutive alpha- and beta-activation of propiolates towards electrophiles, involving conjugate addition of tertiary amines and intramolecular silyl migration

Herein, we present a novel approach for the consecutive alpha- and beta-activation of conjugated alkynes and demonstrate the application of this methodology towards the C-C bond-forming reactions of propiolates. This new concept is based on the 1,4-addition of a tertiary amine to a conjugated alkyne, followed by an aldol-type addition to an aldehyde and subsequent intramolecular silyl migration. This sequential process is generally applicable for 3-trimethylsilylpropiolates. The combination of methyl 3-trimethylsilylpropiolate, 1,4-diazobicyclo[2.2.2]octane (DABCO), and aromatic aldehydes brought about domino-type C-C bond formations to afford highly functionalized olefins as the major products. On the other hand, aliphatic aldehydes, including the sterically demanding aromatic aldehyde, 2,6-dimethylbenzaldehyde, produced alkyne derivatives as the sole products from the reaction, presumably, by the reaction pathway common to the first cases. The intramolecular version of the reaction was successfully applied to the cyclization of trimethylsilylpropiolic esters derived from salicylaldehydes, leading to a new formylcoumarin synthesis. Studies of the reaction mechanisms are also described.

Multicomponent Domino Processes Based on the Organocatalytic Generation of Conjugated Acetylides: Efficient Synthetic Manifolds for Diversity-Oriented Molecular Construction

The organocatalytic generation of a strong base by the action of a good nucleophile is the base for the in situ catalytic generation of conjugated acetylides in the presence of aldehydes or activated ketones. The method is affordable in a multicomponent, domino format able to generate a chemically diverse set of multifunctionalized adducts that are very well suited for diversity-oriented molecular construction. The domino process involves a nucleophile as catalyst and a terminal conjugated alkyne (H-C[triple chemical bond]C-Z) and an aldehyde or activated ketone as building blocks. The chemical outcome of this process changes dramatically as a function of the nucleophile (tertiary amine or phosphine), temperature, stoichiometry, and solvent. These multicomponent domino processes achieve molecular construction with good atom economy and, very importantly, with an exquisite chemo-differentiating incorporation of identical starting units into the products (nondegenerated chemical output). These properties convert the H-C[triple chemical bond]C-Z unit into a specific building block for diversity-oriented molecular construction. Applications to the modular and diversity-oriented synthesis of relevant heterocycles are discussed. A protocol involving two coupled domino processes linked in a one-pot manner will be discussed as an efficient synthetic manifold for the modular and diversity-oriented construction of multisubstituted nitrogen-containing heterocycles.

Nucleoside Analogues from Branched-Chain Pyranosides

Reaction of (pyranosid-3-yl)ethanal 2 with ethynylmagnesium bromide or lithium phenylacetylide in THF afforded (2R,S)-1-(methyl 2-O-benzyl-4,6-O-benzylidene-3-deoxy-α-d-altropyranosid-3-yl)but-3-yn-2-ols 3a and 3b, respectively. Oxidation of 3a and 3b yielded the 1-(methyl 2-O-benzyl-4,6-O-benzylidene-3-deoxy-α-d-altropyranosid-3-yl)but-3-yn-2-ones 4a and 4b, which upon treatment with hydrazine and hydrazine derivatives formed the 3-(methyl 2-O-benzyl-4,6-O-benzylidene-3-deoxy-α-d-altropyranosid-3-ylmethyl)pyrazoles 5a–5d. Compounds 4a and 4b also underwent reaction with amidinium and guanidinium salts under basic conditions to furnish the 4-(methyl 2-O-benzyl-4,6-O-benzylidene-3-deoxy-α-d-altropyranosid-3-ylmethyl)pyrimidines 8a–8f. Furthermore, treatment of 4a and 4b with 2-aminobenzimidazole yielded the 2-(methyl 2-O-benzyl-4,6-O-benzylidene-3-deoxy-α-d-altropyranosid-3-ylmethyl)benzo[4,5]imidazo[1,2-a]pyrimidines 11a and 11b. Deprotection of 5a and 8b in two steps afforded 3(5)-(methyl 3-deoxy-α-d-altropyranosid-3-ylmethyl)-1H(2H)-pyrazole 7 and 4-(methyl 3-deoxy-α-d-altropyranosid-3-ylmethyl)-2-phenylpyrimidine 10, respectively. Compound 11a was treated with AcOH/H2O to furnish 2-(methyl 2-O-benzyl-3-deoxy-α-d-altropyranosid-3-ylmethyl)benzo-[4,5]imidazo[1,2-a]pyrimidine 13.

Alkynoates as a source of reactive alkylinides for aldehyde addition reactions

[see reaction]. The reaction of activated alkynes with carbonyl compounds in the presence of a catalytic amount of a nucleophile leads to enol-protected functionalized propargyl alcohols and 1,3-dioxolane compounds by way of a mild carbon-carbon bond formation reaction.