Search Results (68)

This study explores a disulfide-selective cross-linking strategy for natural rubber (NR) to formulate elastomeric materials with engineering-relevant mechanical properties. A disulfide-containing bismaleimide (BIS) cross-linker was synthesized from cystamine and maleic anhydride and compounded with NR. Three formulations were prepared: control (no inhibitor), CuCl₂-based, and copper(II) methacrylate (CuMA) based compounds, with BIS concentrations ranging from 3.55 to 8.88 phr. Rheological and mechanical testing revealed that CuCl₂ formulations suffered from molecular degradation, poor thermal stability, and mechanical brittleness due to oxidative reactions in the absence of antioxidants. In contrast, CuMA-based compounds exhibited intermediate molecular weights prior to curing, stable thermal behavior, and improved mechanical properties, including enhanced torque and tensile strength, indicating effective cross-linking and partial recyclability. The control formulations also performed reasonably well but did not match the mechanical strength of conventional sulfur-vulcanized NR. The results demonstrate that metal coordination, particularly with CuMA, can modulate disulfide metathesis kinetics and offer a pathway to thermally triggered network rearrangement. Overall, CuMA emerges as a promising candidate for developing high-performance, recyclable rubber materials, while CuCl₂ requires further stabilization strategies. This work establishes a baseline for future recyclability studies and advances the design of dynamic covalent networks in elastomers. Full article

Lagunamide D is a structurally distinct 26-membered cytotoxic cyclic depsipeptide, originally isolated from a marine cyanobacterium. It exhibits potent antiproliferative activity in the low nanomolar range against A549 human lung adenocarcinoma cells and HCT116 colon cancer cells. A significant challenge associated with lagunamide D is its propensity for intramolecular acyl migration, which leads to the formation of a contracted 24-membered analog, lagunamide D′. This structural rearrangement complicates its isolation, characterization, and synthesis. In this study, the total synthesis of lagunamide D was achieved in a 14-step longest linear sequence, starting from the known intermediate 17, with an overall yield of 4.6%. The synthetic strategy involved several key transformations, including Ghosh’s TiCl₄-promoted anti-aldol reaction, Corey–Bakshi–Shibata reduction (CBS reduction), cross-metathesis, Pinnick oxidation, and Yamaguchi esterification. Furthermore, this synthetic effort unambiguously confirmed the stereochemistry of the natural product. Full article

Metathesis homo- and copolymerization of bifunctional monomers bearing two norbornene moieties was studied. The monomers were synthesized from cis-5-norbornene-exo-2,3-dicarboxylic anhydride and various diamines (hexamethylenediamine, decamethylenediamine, 1R,3S-isophoronediamine). The metathesis homopolymerization of these bis(nadimides) in the presence of the second-generation Grubbs catalyst afforded glassy cross-linked polymers in more than 90% yields. The metathesis copolymerization of the bis(nadimides) and a monofunctional norbornene derivative containing the β-pinene fragment also resulted in insoluble cross-linked polymers in nearly quantitative yields. The structures and purity of the synthesized polymers were confirmed via IR spectroscopy and CP/MAS NMR spectroscopy. Conditions for the fabrication of mechanically strong solution-cast thin films based on copolymers synthesized from the comonomers mentioned above were determined by varying the content of the cross-linking agent. It was shown that the films made in this way are stable in a range of organic solvents and could be useful as semipermeable or membrane materials for use in liquid organic media. The permeability of the polymer films in question to 1-phenylethanol and mandelic acid was studied. The results obtained are discussed along with the data from the DSC, TGA, and powder X-ray diffraction studies of the properties of the synthesized metathesis homo- and copolymers. Full article

A novel and concise synthetic method for arenastatin A, a cytotoxic cyclic depsipeptide of marine origin, was developed in this study. The convergent assembly of the four segments, including the cross-metathesis reaction, gave a cyclization precursor, and Fmoc deprotection caused simultaneous macrocyclization. The Corey–Chaykovsky reaction using a chiral sulfur ylide afforded arenastatin A with complete stereoselectivity in the longest linear sequence of seven reaction steps from the known compound. Using this synthetic method, some analogs of segment B were prepared through a late-stage diversification strategy. The simple S_N2 reaction of the thiolate toward the tosylate precursor, prepared using almost the same synthetic method as described above, provided the desired sulfide analogs. Full article

The absolute stereochemical configurations of acremolides A and B were predicted by a biochemistry-based rule and unambiguously confirmed through their total syntheses. The features of the total syntheses include sequential Krische’s Ir-catalyzed crotylation, Brown’s borane-mediated crotylation, Mitsunobu esterification reaction, and cross-metathesis reaction. The efficient total synthesis enabled clear validation of the predicted stereochemistry for acremolides A and B. Full article

Naturally occurring carbohydrates serve as useful building blocks, and various derivatives have been employed in natural product syntheses. For instance, some aldoses can be converted to 1,3-dienes via the Wittig reaction at the anomeric carbon, accompanied by the E2 elimination of the C3-alkoxy group. However, there are few examples of terminal 1,3-diene synthesis. We report the synthesis of (S,Z)-1,4-bis(benzyloxy)hexa-3,5-dien-2-ol, featuring a terminal 1,3-diene and chiral secondary alcohol, derived from 2,3,5-tri-O-benzyl-d-arabinofuranose with methyltriphenylphosphonium bromide and potassium tert-butoxide in a single step. The synthesized terminal 1,3-diene demonstrated effective reactivity in a cross-metathesis reaction with cis-1,4-diacetoxy-2-butene. Full article

The rate constants of elementary processes in the atom–diatom system $\mathrm{O}{(}^{3}P)+{\mathrm{H}}_2\left(v\right)$, including the processes of vibrational relaxation and dissociation, were studied using the quasiclassical trajectory method. All calculations were carried out along the ground potential energy surface (PES) ³$A^{″}$ that was approximated by a neural network. Approximation data were obtained using ab initio quantum chemistry methods at the extended multi-configuration quasi-degenerate second-order perturbation theory XMCQDPT2 in a basis set limit. The calculated cross-sections of the reaction channels are in good agreement with the literature data. A complete set of state-to-state rate constants was obtained for the metathesis reaction, the dissociation and relaxation of the H₂ molecule upon collision with an O atom. According to these data, Arrhenius approximations over a wide temperature range were obtained for the thermal rate constants of considered processes. Data obtained on the dissociation constants and VT relaxation of vibrationally excited H₂ molecules can be used in constructing kinetic models describing the oxidation of hydrogen at high temperatures or highly nonequilibrium conditions. Full article

This review article discusses the recent progress in synthesizing seven-membered ring 1,3,5-triazepine and benzo[f][1,3,5]triazepine derivatives. These derivatives can be either unsaturated, saturated, fused, or separated. This review covers strategies and procedures developed over the past two decades, including cyclo-condensation, cyclization, methylation, chlorination, alkylation, addition, cross-coupling, ring expansions, and ring-closing metathesis. This review discusses the synthesis of 1,3,5-triazepine derivatives using nucleophilic or electrophilic substitution reactions with various reagents such as o-phenylenediamine, 2-aminobenzamide, isothiocyanates, pyrazoles, thiazoles, oxadiazoles, oxadiazepines, and hydrazonoyl chloride. This article systematically presents new approaches and techniques for preparing these compounds. It also highlights the biological importance of benzo[f][1,3,5]triazepine derivatives, which have been used as drugs for treating nervous system diseases. This review aims to provide researchers with the necessary information to create and develop new derivatives of these compounds as quickly as possible. Full article

In 2021, global plastics production was 390.7 Mt; in 2022, it was 400.3 Mt, showing an increase of 2.4%, and this rising tendency will increase yearly. Of this data, less than 2% correspond to bio-based plastics. Currently, polymers, including elastomers, are non-recyclable and come from non-renewable sources. Additionally, most elastomers are thermosets, making them complex to recycle and reuse. It takes hundreds to thousands of years to decompose or biodegrade, contributing to plastic waste accumulation, nano and microplastic formation, and environmental pollution. Due to this, the synthesis of elastomers from natural and renewable resources has attracted the attention of researchers and industries. In this review paper, new methods and strategies are proposed for the preparation of bio-based elastomers. The main goals are the advances and improvements in the synthesis, properties, and applications of bio-based elastomers from natural and industrial rubbers, polyurethanes, polyesters, and polyethers, and an approach to their circular economy and sustainability. Olefin metathesis is proposed as a novel and sustainable method for the synthesis of bio-based elastomers, which allows for the depolymerization or degradation of rubbers with the use of essential oils, terpenes, fatty acids, and fatty alcohols from natural resources such as chain transfer agents (CTA) or donors of the terminal groups in the main chain, which allow for control of the molecular weights and functional groups, obtaining new compounds, oligomers, and bio-based elastomers with an added value for the application of new polymers and materials. This tendency contributes to the development of bio-based elastomers that can reduce carbon emissions, avoid cross-contamination from fossil fuels, and obtain a greener material with biodegradable and/or compostable behavior. Full article

The first total syntheses of cyclic depsipeptides colletopeptide A and colletotrichamide A, have been accomplished. The key advanced intermediate, a cyclic tridepsipeptide derivative, was constructed using a sequence of transformations that features asymmetric Brown crotylation, cross metathesis, Yamaguchi esterification, ozonolysis, and macrolactamization. A late-stage incorporation of the mannose fragment completed the synthesis of colletotrichamide A, and the desilylation of the common intermediate gave rise to colletopeptide A, which led to unambiguous confirmation of the absolute stereochemistry of the aforementioned natural products. Full article

Recently, sterically demanding N-heterocyclic cyclometalated ruthenium were reported as efficient Z-selective catalysts for cross-metathesis, showing a different reactivity in the function of the auxiliary ligand and the bulky ligand. To understand the origin of this behavior, we carried out density functional (M06-L) calculations to explore the reaction mechanism and insight from the energetic contributions into the determinant step. We emphasize the differences that occur when the 2,6-diisopropylphenyl (Dipp) and 2,6-diisopentylphenyl (Dipep) are employed. The results show that the barrier energies, $\Delta G^{‡}$, increase when the bulky ligand is greater, using nitrate as an auxiliary ligand, while the opposite behavior is obtained when pivalate is the auxiliary ligand. This tendency has its origin in the low reorganization energy and the less steric hindrance (%V_bur) obtained in catalysts that involve nitrate ligand and Dipep group. Moreover, by scrutinizing the energy decomposition analysis (EDA), it is found that the electronic contributions are also dominant and are not uniquely the steric effects that control the Z-selectivity. Full article

Ruthenium-catalyzed cross metathesis using biseugenol (1) with electron-deficient olefins methyl (2a) and ethyl (2b) acrylates, acrylic acid (2c), acrylonitrile (2d), and methyl methacrylate (2e) derivatives have been conducted to afford respective derivatives 3a–3e with good yields and excellent conversion rates. Activity of prepared compounds against trypomastigote and amastigote forms of Trypanosoma cruzi and mammalian cytotoxicity have been evaluated. The results obtained indicate that the IC₅₀ values for amastigotes of compounds 3b and 3d are quite similar to those of biseugenol (1), but unlike this compound, they show reduced toxicities with SI values similar to those of the standard drug benznidazol. Full article

Symmetrical and dissymmetrical bolaforms were prepared with good to high yields from unsaturated L-rhamnosides and phenolic esters (ferulic, phloretic, coumaric, sinapic and caffeic) using two eco-compatible synthetic strategies involving glycosylation, enzymatic synthesis and cross-metathesis under microwave activation. The plant-eliciting activity of these new compounds was investigated in Arabidopsis model plants. We found that the monocatenar rhamnosides and bolaforms activate the plant immune system with a response depending on the carbon chain length and the nature of the hydrophilic heads. Their respective antioxidant activities were also evaluated, as well as their cytotoxic properties on dermal cells for cosmetic uses. We showed that phenolic ester-based compounds present good antioxidant activities and that their cytotoxicity is low. These properties are also dependent on the carbon chains used. Full article

A versatile strategy for the enantioselective synthesis of a benzo[c]oxepine structural core containing natural secondary metabolites was developed. The key steps of the synthetic approach include ring-closing alkene metathesis for seven-member ring construction, the Suzuki–Miyaura cross-coupling reaction for the installation of the double bond and Katsuki–Sharpless asymmetric epoxidation for the introduction of chiral centers. The first total synthesis and absolute configuration assignment of heterocornol D (3a) were achieved. Four stereoisomers, 3a, ent-3a, 3b and ent-3b, of this natural polyketide were prepared, starting with 2,6-dihydroxy benzoic acid and divinyl carbinol. The absolute and relative configuration of heterocornol D was assigned via single-crystal X-ray analysis. The extension of the described synthetic approach is further presented with the synthesis of heterocornol C by applying the ether group reduction method to the lactone. Full article

Fluorinated polymers are attractive due to their special thermal, surface, gas separation, and other properties. In this study, new diblock, multiblock, and random copolymers of cyclooctene with two fluorinated norbornenes, 5-perfluorobutyl-2-norbornene and N-pentafluorophenyl-exo-endo-norbornene-5,6-dicarboximide, are synthesized by ring-opening metathesis copolymerization and macromolecular cross-metathesis in the presence of the first- to third-generation Grubbs’ Ru-catalysts. Their thermal, surface, bulk, and solution characteristics are investigated and compared using differential scanning calorimetry, water contact angle measurements, gas permeation, and light scattering, respectively. It is demonstrated that they are correlated with the chain structure of the copolymers. The properties of multiblock copolymers are generally closer to those of diblock copolymers than of random ones, which can be explained by the presence of long blocks capable of self-organization. In particular, diblock and multiblock fluorine-imide-containing copolymers show a tendency to form micelles in chloroform solutions well below the overlap concentration. The results obtained may be of interest to a wide range of researchers involved in the design of functional copolymers. Full article