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Other enantioselective reactions catalyzed by transition metals
Published in Ilya D. Gridnev, Pavel A. Dub, Enantioselection in Asymmetric Catalysis, 2016
Organoboronic acids, such as phenylboronic acid, are important in organic synthesis and medicinal chemistry because of their versatility as synthons in the preparation of complex molecules.66 The use of organoboronic acids is also attractive due to very high stabilities in protic and aqueous media and commercial availability in a variety of forms. The Pd- and Rh-catalyzed conjugated addition of organoboronic acids to enones and nitrostyrenes (Hayashi–Miyaura reaction) is a powerful tool for enantioselective Michael addition.67,68 Indeed, the reaction is characterized by (a) no competitive uncatalyzed reaction of the organoboronic acids onto the enone; (b) no 1,2-addition of the organoboron reagent; and (c) a large functional group tolerance which is in contrast to organolithium and Grignard reagents.69 Addition of arylboronic acids to enones was pioneered by Uemura (M = Pd)70 and Miyaura (M = Rh,71 M = Pd72,73) in the mid-1990s. Hayashi (M = Rh),74–77 Miyaura (M = Rh,77 M = Pd78), and Minnaard (M = Pd)79 reported the first asymmetric versions. The Hayashi group developed the first rhodium-catalyzed highly enantioselective addition of arylboronic acids to α-substituted nitroalkenes employing a Rh/Binap catalyst.80 The Gutnov group reported the enantioselective addition of arylboronic acids to strongly activated 2-nitroacrylate using Miyarua’s cationic chiraphos/Pd catalytic system,81 whereas Yang and Zhang82 reported first Pd-catalyzed enantioselective Michael addition of arylboronic acids to nitroalkenes with a broad substrate scope.
Phenylboronic acid modified hydrogel materials and their potential for use in contact lens based drug delivery
Published in Journal of Biomaterials Science, Polymer Edition, 2022
Lina Liu, Talena Rambarran, Heather Sheardown
In the current work, a novel chemistry was used to modify the properties of hydrogel polymers used in contact lens manufacturing. Specifically, it was hypothesized that polymeric materials containing PBA may be useful in enhancing adhesion of wetting agents while also impacting ophthalmic drug bioavailability by modulating the release. Phenylboronic acid (PBA) is a synthetic boronic acid containing ligand, which can form a complex with mucins by binding oligosaccharide side chains in a neutral or weakly basic environment (at pH 7–9) [31–33]. Studies have demonstrated that boronate-containing materials exhibit the ability to bind saccharide wetting agents due to intermolecular interaction of the boron atom with n-acetyl groups and diol groups of sugars, polysaccharides, nucleotides, glycoproteins [34–36]. These materials have been previously used for the development of glucose sensors owing to their sugar binding properties [37–40]. Hyaluronic acid (HA) and hydroxypropyl guar (HPG) are natural polysaccharide wetting agents that have been used in contact lens applications; the binding of these sugars to PBA has been previously demonstrated [41]. Optionally, the PBA modified materials could bind mucin itself on their surface with the goal of creating biomimetic surfaces to facilitate improved interactions of the material with the ocular surface. Furthermore, the presence of the hydrophobic PBA moiety in the structure of the hydrogel should prove useful for modulating the release of more hydrophobic drugs from the lens materials.
BNPs@Cur-Pd as a versatile and recyclable green nanocatalyst for Suzuki, Heck and Stille coupling reactions
Published in Journal of Experimental Nanoscience, 2020
Muhammed Ali Jani, Kiumars Bahrami
The catalytic activity of BNPs@Cur-Pd nanocatalyst was evaluated in the carbon-carbon cross-coupling reactions including Suzuki–Miyaura, Heck and Stille reactions. In these reactions, some aryl halides reacted with phenylboronic acid, butyl acrylate, and triphenyltin chloride, respectively. In our first experiments, the Suzuki–Miyaura reaction between iodobenzene and phenylboronic acid was selected as a model reaction by using BNPs@Cur-Pd to optimize the effects of solvent, base, the amount of catalyst and temperature. Table 1 shows the obtained optimization conditions for Suzuki’s reactions. In the absence of nanocatalyst, no coupling reaction has taken place in entry 1. At the beginning of the study, PEG was used as a solvent and sodium carbonate (Na2CO3) as a base by using 5–15 mg of BNPs@Cur-Pd at 80 °C (entries 2–5). The optimum results were obtained by 12 mg (0.043 × 10−5 mol g−1, 0.043 mol% Pd) of the BNPs@Cur-Pd nanocatalyst (entry 4). Increasing the amount of nanocatalyst did not show a noticeable improvement in the efficiency of the reaction (entry 6).
Synthesized of glucose-responsive nanogels labeled with fluorescence molecule based on phenylboronic acid by RAFT polymerization
Published in Journal of Biomaterials Science, Polymer Edition, 2019
A kind of novel amphiphilic sugar-responsive nanogels based on phenylboronic acid was synthesized by RAFT polymerization in the mixture solvent of H2O/ethanol. The fluorescence molecule BODIPYMA was incorporated into nanogels, and the fluorescent intensity varied dependent on the glucose concentrations measured by fluorescence emission spectrum and UV spectrophotometer. The formed nanogels could effectively load insulin with the EE and LC up to 64% and 8.2%, respectively. The drug release was dependent on the content of AAPBA moieties in nanogels and glucose concentrations in release medium with a burst release phase. Generally, insulin is injected before dinner to avoid the occurrence of high blood sugar after dinner. The burst release of insulin from nanogels as early as 30 min facilitate a decrease in the postprandial blood sugar of the patients. Moreover, the biocompatibility of nanogels bearing phenylboronic acid was improved by introduction of carbohydrate moieties. The biocompatible and glucose-sensitive nanogels have the potential for use in a self-regulated insulin delivery system in biomedical fields.