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

Hydrothiolation of Triisopropylsilyl Acetylene Sulfur Pentafluoride - Charting the Chemical Space of β-SF5 Vinyl Sulfides

Recently, we suggested liquid and high-boiling TIPS-CC-SF5 (TASP) as a versatile reagent to access so far elusive SF5-containing building blocks by less specialized laboratories under bench-top conditions. The synthesis of non-aromatic SF5 building blocks generally requires on-site fluorination or pentafluorosulfanylation steps employing toxic and/or gaseous reagents. Herein, we underline the versatility of this reagent by reporting a benign bench-top protocol for the synthesis of Z-configured β-pentafluorosulfanylated vinyl sulfides in good to excellent yields (up to 99 %) with exclusive (Z)-diasteroselectivity and broad functional group tolerance. This method exploits an in-situ protodesilylation-hydrothiolation sequence. This so far uncharted class of compounds was characterized by means of NMR-spectroscopy as well as SC-XRD. Furthermore, we suggest the reaction to proceed via a kinetically controlled closed-shell reaction pathway, corroborated by in-silico experiments.

CuI-catalyzed regioselective hydrothiolation of alkynes: a thiol-free route to (Z)-β-alkenyl sulfides

A thiol-free procedure for regioselective preparation of (Z)-β-alkenyl sulfides via a three-component reaction of aryl/alkyl halides, phenylacetylene, and potassium isopropylxanthate in the presence of copper iodide as a catalyst in polyethylene glycol is reported. In this study, a xanthate salt is used as an odorless source of sulfur. The reactions proceed in a one-pot and single-step pathway with the formation of the carbothionate intermediate identified using NMR data as well as exclusively forming the Z isomer.

Design and synthesis of unnatural coordination glycopolymer particles (CGPs): unleashing the potential of catechol-saccharide derivatives

Our study unveils an innovative methodology that merges catechols with mono- and disaccharides, yielding a diverse array of compounds. This strategic fusion achieves robust yields and introduces ligands with a dual nature: encompassing both the chelating attributes of catechols and the recognition capabilities of carbohydrates. This synergistic design led us to couple one of the novel ligands with an Fe(iii) salt, resulting in the creation of Coordination Glycopolymer Particles (CGPs). These CGPs demonstrate remarkable qualities, boasting outstanding dispersion in both aqueous media and Phosphate Buffered Saline (PBS) solution (pH ∼7.4) at higher concentrations (0.26 mg μL-1). Displaying an average Z-size of approximately 55 nm and favourable polydispersity indices (<0.25), these particles exhibit exceptional stability, maintaining their integrity over prolonged periods and temperature variations. Notably, they retain their superior dispersion and stability even when subjected to freezing or heating to 40 °C, making them exceptionally viable for driving biological assays. In contrast to established methods for synthesizing grafted glycopolymers, where typically a glycopolymer is doped with catechol derivatives to create synergy between chelating properties and those inherent to the saccharide, our approach provides a more efficient and versatile pathway for generating CGPs. This involves combining catechols and carbohydrates within a single molecule, enabling the fine-tuning of organic structure from a monomer design step and subsequently transferring these properties to the polymer.

Hydrothiolation of alkynes with thiol-catechol derivatives catalysed by CuNPs/TiO2: exploring the reaction mechanism by DFT calculations

Density functional theory (DFT) calculations were applied to describe the hydrothiolation reaction of activated alkynes with thiols bearing a catechol group. The thiol-yne click (TYC) process was efficiently catalysed by a CuNPs/TiO₂ nanocatalyst giving the corresponding anti-Markovnikov vinyl sulphides with high Z-stereoselectivity. Based on the experimental results and DFT studies, a plausible reaction mechanism is proposed, which implies the activation of the carbon-carbon triple bond by coordination to the copper centre, followed by a stereoselective (external) nucleophilic attack to give preferentially the Z-vinyl sulphide isomer. Additionally, experimental and theoretical studies strongly correlate with the proposed synergistic role for the TiO₂ support in the catalytic process.

B(C6F5)3-Catalyzed [4 + 2] Cyclization Strategy: Synthesis and Photophysical Properties of 5H-Naphtho[2,3-c]carbazole-8,13-dione Derivatives

In this paper, a series of novel carbazolequinones were efficiently obtained by a B(C₆F₅)₃-catalyzed [4 + 2] cyclization reaction. This protocol not only had a simple operation, broad substrate range, and high atomic economy, but also had a low catalyst loading and avoided using metal catalysts. In addition, we constructed diverse new carbazole-fused compounds under different reduction conditions. The results of photophysical characterization showed that the structure of carbazole-fused derivatives had a significant impact on the fluorescence properties.

Novel pH-sensitive catechol dyes synthesised by a three component one-pot reaction

The synthesis and characterisation of new dyes based on indolizines bearing catechol groups in their structure is presented. The preparation was carried out through a simple three component one-pot reaction promoted by CuNPs/C, between pyridine-2-carbaldehyde, an aromatic alkyne and a tetrahydroisoquinoline (THIQ) functionalized with catechol groups. The products were isolated in 30%-34% yield, which was considered more than acceptable considering that the catechol hydroxyl groups were not protected prior to reaction. In view of the colour developed by the products and their response to the acidic and basic conditions of the medium, product 3aa was studied by UV-Vis and NMR spectroscopies at different pH values. We concluded that product 3aa suffered two deprotonations at pK_a of 4.4 and 9.5, giving three species in a pH range between 2-12, with colours varying from light red to deep orange. The reversibility of the process observed for 3aa at different pH values, together with its changes in colour, make this new family of products attractive candidates to use them as pH indicators.

Mussel-Inspired Lego Approach for Controlling the Wettability of Surfaces with Colorless Coatings

The control of surface wettability with polyphenol coatings has been at the forefront of materials research since the late 1990s, when robust underwater adhesion was linked to the presence of L-DOPA-a catecholic amino acid-in unusually high amounts, in the sequences of several mussel foot proteins. Since then, several successful approaches have been reported, although a common undesired feature of most of them is the presence of a remnant color and/or the intrinsic difficulty in fine-tuning and controlling the hydrophobic character. We report here a new family of functional catechol-based coatings, grounded in the oxidative condensation of readily available pyrocatechol and thiol-capped functional moieties. The presence of at least two additional thiol groups in their structure allows for polymerization through the formation of disulfide bonds. The synthetic flexibility, together with its modular character, allowed us to: (I) develop coatings with applications exemplified by textiles for oil-spill water treatment; (II) develop multifunctional coatings, and (III) fine-tune the WCA for flat and textile surfaces. All of this was achieved with the application of colorless coatings.

Synthesis and Antioxidant Activity of New Catechol Thioethers with the Methylene Linker

Novel catechol thio-ethers with different heterocyclic substituents at sulfur atom were prepared by reacting 3,5-di-tert-butyl-6-methoxymethylcatechol with functionalized thiols under acidic conditions. A common feature of compounds is a methylene bridge between the catechol ring and thioether group. Two catechols with the thio-ether group, bound directly to the catechol ring, were also considered to assess the effect of the methylene linker on the antioxidant properties. The crystal structures of thio-ethers with benzo-thiazole moieties were established by single-crystal X-ray analysis. The radical scavenging and antioxidant activities were determined using 2,2′-diphenyl-1-picrylhydrazyl radical test, ABTS^∙+, CUPRAC (TEAC) assays, the reaction with superoxide radical anion generated by xanthine oxidase (NBT assay), the oxidative damage of the DNA, and the process of lipid peroxidation of rat liver (Wistar) homogenates in vitro. Most catechol-thioethers exhibit the antioxidant effect, which varies from mild to moderate depending on the model system. The dual anti/prooxidant activity characterizes compounds with adamantyl or thio-phenol substituent at the sulfur atom. Catechol thio-ethers containing heterocyclic groups (thiazole, thiazoline, benzo-thiazole, benzo-xazole) can be considered effective antioxidants with cytoprotective properties. These compounds can protect molecules of DNA and lipids from the different radical species.

Synthesis and Structural Studies of Cu(I) Methylthiosalicylate Complexes and their Catalytic Application in Thiol-Yne Click Reaction

Three complexes of Cu(I), [Cu(PPh3)2(mts)] (1), [Cu(dppf)(mts)] (2), [Cu(dppe)(mts)]2 (3) (mts = methylthiosalicylate; dppf = dipheylphosphinoferrocene; dppe = diphenylphosphinoethane) have been synthesized and characterized. Complexes 1 and 2 have monomeric...

Click reaction in the synthesis of dendrimer drug-delivery systems

Drug delivery systems are technologies designed for the targeted delivery and controlled release of medicinal agents. Among the materials employed as drug delivery systems, dendrimers have gained increasing interest in recent years because of their properties and structural characteristics. The use of dendrimer-nanocarrier formulations enhances the safety and bioavailability, increases the solubility in water, improves stability and pharmacokinetic profile, and enables efficient delivery of the target drug to a specific site. However, the synthesis of dendritic architectures through convergent or divergent methods has drawbacks and limitations that disrupt aspects related to design and construction and consequently slow down the transfer from academia to industry. In that sense, the implementation of click chemistry has been received increasing attention in the last years, because offers new efficient approaches to obtain dendritic species in good yields and higher monodispersity. This review focuses on recent strategies for building dendrimer drug delivery systems using click reactions from 2015 to early 2021. The dendritic structures showed in this review are based on β-cyclodextrins (β-CD), poly(amidoamine) (PAMAM), dendritic poly (lysine) (PLLD), dimethylolpropionic acid (bis-MPA), phosphoramidate (PAD), and poly(propargyl alcohol-4-mercaptobutyric (PPMA).

Systematic Study of Aromatic-Ring-Targeted Cycloadditions of 5-Hydroxymethylfurfural Platform Chemicals

The reaction space of the furanics-to-aromatics (F2A) conversion process for 5-hydroxymethylfurfural (HMF)-based platform chemicals has been explored both experimentally and by quantum chemistry methods. For the first time, a structure-activity relationship was established in furan-yne cycloaddition for a number of different HMF derivatives. Correlations between the activation energy of the cycloaddition stage and the structure of the substrates were established by molecular modeling methods. Analysis of the concerted and stepwise mechanisms of cycloaddition in the singlet and triplet electronic states of the molecular system was carried out. A series of biobased 7-oxanorbornadienes was obtained in the reaction with dimethyl acetylenedicarboxylate. Various methods of aromatization of the obtained [4+2] adducts have been examined. Rearrangement catalyzed by a Lewis acid leads to the formation of a phenol derivative, whereas reduction by diiron nonacarbonyl leads to the formation of functionalized benzene. Systematic study of the cycloaddition process has revealed a simple way to analyze and predict the relative reactivity of furanic substrates.

Computational Study of the Addition of Methanethiol to 40+ Michael Acceptors as a Model for the Bioconjugation of Cysteines

A long series of Michael acceptors are studied computationally as potential alternatives to the maleimides that are used in most antibody-drug conjugates to link Cys of mAbs with cytotoxic drugs. The products of the reaction of methanethiol (CH3SH/MeSH, as a simple model of Cys) with N-methylated ethynesulfonamide, 2-ethynylpyridinium ion, propynamide, and methyl ethynephosphonamidate (that is, with HC≡C-EWG) are predicted by the M06-2X/6-311+G(d,p) method to be thermodynamically more stable, in relation to their precursors, than that of MeSH with N-methylmaleimide and, in general, with H2C═CH-EWG; calculations with AcCysOMe and tBuSH are also included. However, for the addition of the anion (MeS-), which is the reactive species, the order changes and N-methylated 2-vinylpyridinium ion, 2,3-butadienamide, and maleimide may give more easily the anionic adducts than several activated triple bonds; moreover, the calculated ΔG⧧ values increase following the order HC≡C-SO2NHMe, N-methylmaleimide, HC≡C-PO(OMe)NHMe, and HC≡C-CONHMe. In other words, MeS- is predicted to react more rapidly with maleimides than with ethynephosphonamidates and with propynamides, in agreement with the experimental results. New mechanistic details are disclosed regarding the advantageous use of some amides, especially of ethynesulfonamides, which, however, are more prone to double additions and exchange reactions.