Application of phenylboric acid_Kain Industrial Additive

Background and overview^[1][2][3]

Phenylboronic acid is a white solid. Melting point: 215~216°C (anhydride), Ka13.7, solubility at 25°C: 1.75% (benzene), 1.2% (xylene), 30.2% (ether), 178% (methanol), 2.5% (water). Phenylboronic acid, as a fully synthetic polyhydroxy compound recognizer, has the advantages of being cheap, stable and difficult to inactivate compared to enzymes. Therefore, it has attracted the attention and attention of many researchers in the past few decades. .

At present, its application in separation and sensor is relatively mature; however, in the application of drug delivery system and tissue engineering, there are still some problems that need to be solved, such as physiological pH value (7.4) and physiological temperature (37℃ ) conditions, existing phenylboronic acid derivatives have low recognition ability for glucose and sialic acid, and poor selectivity for polyhydroxy substances in body fluids. However, due to its broad application prospects and important social significance and economic value, it still receives widespread international attention.

Phenylboronic acid derivatives have two charged and uncharged forms in aqueous solution. Only the charged form can form reversible interactions with polyhydroxy compounds having 1,2- or 1,3-diol groups. Five-membered or six-membered ring esters, this process is reversible, and there are a large number of such polyhydroxy compounds in nature, such as polysaccharides and other substances. Many of them exist in organisms and have an important impact on the life activities of organisms. Therefore, In addition to detecting, separating and purifying these compounds, phenylboronic acid can also be used to identify polyhydroxy substances in the body for autonomous drug delivery systems or to regulate certain life activities. Therefore, phenylboronic acid and its derivatives have attracted the attention and attention of many researchers.

Apply^[2]

1. Research on the role of autonomous insulin delivery system

Diabetes is a metabolic disease with multiple causes, characterized by chronic hyperglycemia, accompanied by disorders of sugar, fat, and protein metabolism caused by defects in insulin secretion and/or action. For people with insulin-dependent diabetes, long-term subcutaneous injections of insulin are required, making the treatment poorly tolerated. The blood glucose-sensing autonomous insulin delivery system can adjust the release of insulin according to blood glucose concentration, thereby increasing the tolerance of treatment and preventing the occurrence of hypoglycemia. It is an ideal delivery method.

Phenylboronic acid can form a complex with glucose, so in recent years it has been introduced into drug delivery systems as a glucose concentration-responsive monomer in order to self-regulate the release of insulin. After glycosylation modification, insulin was bound to gel microspheres with a phenylboronic acid content of 4% (mol). When glucose is present, glycosylated insulin is shed due to its competitive substitution for the phenylboronic acid site.

They found that small changes in glucose concentration can cause rapid release of insulin, and that pulse-type drug release can be achieved with pulse-type changes in glucose concentration. After introducing amino groups into phenylboronic acid gel, the stability of phenylboronic acid ions can be enhanced, the number of phenylboronic acid complexes can be increased under physiological pH conditions, the insulin loading capacity can be increased, and the release time in response to glucose can be as long as 120 h.

2. Application research in tissue engineering

Almost all biological cell membranes contain glycosylated substances such as glycolipids or glycoproteins, with varying numbers of hydroxyl groups (for example, gangliosides are ceramides with varying numbers of sugar residues), so they have Binding site for phenylboronic acid. This characteristic makes the application of phenylboronic acid in tissue engineering attract more and more attention. Study the binding behavior of PAPBA and JV-acetylneuraminic acid (Neu5Ac, sialic acid) in solutions with different pH values.

Studies have shown that because the amino group at C.5 position in Neu5Ac has a stabilizing effect on the boron atom, the binding constant between PAPBA and Neu5Ac is 7 times the binding constant between PAPBA and glucose at a physiological pH value of 7-4. This indicates that Neu5Ac may be the main receptor during the interaction between phenylboronic acid and biological membranes. Phenylboronic acid and polyethylene glycol (PEG) were grafted onto the polyL-lysine (PLL) backbone, respectively. PBA serves as the binding site of the copolymer and can bind to the cis-hydroxyl groups on receptors such as glycolipids and glycoproteins on biological membranes, while PEG serves as the non-binding site

It can prevent the binding of exogenous lectins and antibodies. By adjusting the contents of PBA and PEG in the copolymer, it can be stably bound to cells and form a PEG protective layer outside the cells. Therefore, this copolymer can be used to prevent cell aggregation caused by antibody adhesion to red blood cells after transfusion and to prevent neutrophil adhesion to vascular endothelial cells after reperfusion.

3. Research on biological material separation systems

Phenylboronic acid can be combined with polyhydroxy compounds and has many uses in the separation of biological substances. In the chromatographic separation method, introducing phenylboronic acid monomer into the stationary phase has a better separation effect on polysaccharides, glycolipids, nucleotides and other substances. The "multi-step microsuspension polymerization method" was used to prepare uniform porous particles containing phenylboronic acid with a particle size of about 10 um, and its effect on B. nicotinamide adenine dinucleotide (~-NAD) was investigated as a model molecule. Adsorption and desorption behavior of dihydroxy compounds.

Using such uniform particles as the stationary phase of affinity high-performance liquid chromatography can improve the flow parameters and separation efficiency of the chromatographic column, and is expected to be used for the separation and determination of glycoproteins in plasma. Phenylboronic acid can also be introduced in membrane separation. The feasibility of using a support liquid membrane containing phenylboronic acid monomer to separate fructose in a fermentation tank was studied, and it was found that the selective separation coefficient of the hollow fiber membrane for fructose/glucose can reach 20. Although the stability and flow rate of the membrane need to be further improved, the membrane still has good application prospects.

4. Application research in sensors

There have been many research reports on introducing phenylboronic acid into sensors for the quantitative detection of polysaccharides and other polyhydroxyl substances. Use phenylboric acid and other monomers to form a thin film on the surface of the gold electrode. When phenylboric acid combines with sugars in the solution, the electrolyte properties of the film change, causing changes in current, and this change is related to the sugars. Concentration-dependent and thus can be used for quantitative detection of polysaccharides. There are also studies that synthesized thiol compounds containing phenylboronic acid and assembled them on the gold surface to form a self-assembled film TGA-PBA/Au, which can achieve high-sensitivity detection of monosaccharides.

On the other hand, phenylboronic acid was introduced into the gel base material and the hologram of the system was observed: when substances such as glucose combine with it, the gel swells, causing the diffraction wavelength of the hologram to red-shift, using This property enables quantitative detection of glucose concentration. This system can be used for real-time monitoring of cell growth. If biocompatible materials are used as the gel substrate, it can be used as a selective holographic sensor for glucose concentration in body fluids. If a fluorescent group is introduced into phenylboronic acid, its binding behavior with glucose and other substances will lead to changes in fluorescence. Based on this property, a more sensitive fluorescence method for detecting glucose and other substances can be designed.

There have been many studies in this area, and there are related reviews. Since blood glucose concentration is very important for the diagnosis and treatment of diabetes, many researchers are committed to developing non-invasive technology that can continuously monitor blood glucose concentration in the body. By embedding a water-soluble phenylboronic acid derivative containing a fluorescent group into an existing lens that has been optimized for vision adjustment and oxygen permeability, the lens can quickly and harmlessly detect the glucose concentration in tears, and then obtain blood glucose. concentration, so it is an ideal instrument for real-time monitoring of blood glucose concentration in diabetics.

Preparation^[2]

Within 1 hour, 0.25 mol of phenylmagnesium bromide (approximately 1 molar solution) was added to a solution of 58 g (0.25 mol) of n-butyl borate dissolved in 100 ml of pure ether. During the reaction the solution was mechanically stirred and cooled with a solid carbon dioxide and acetone bath to maintain the internal temperature between -70°C and -75°C. When the Grignard reagent is dropped into the reaction solution, a white precipitate immediately forms, and the precipitate slowly dissolves. After the Grignard reagent is added, continue stirring the reaction mixture (at -75°C) until the precipitate is completely dissolved.

The resulting orange solution is slowly warmed to 0°C in a cold water bath (preferably overnight). Under vigorous stirring, the reaction mixture was slowly added to 150 ml of cold 10% sulfuric acid, and the ether layer was separated. The aqueous layer was extracted with 2 100 ml portions of diethyl ether. Combine the original ether layer and the ether extract, and evaporate the ether on a steam bath. The residual liquid contains phenylboric acid and n-butanol, which should be treated with potassium hydroxide solution until the solution becomes obviously alkaline. Add enough water to form about 150 ml of water layer below the alcohol layer.

Heat gently under reduced pressure <not exceeding 45℃), steam distillation to evaporate n-butanol, slowly add some warm water as needed, and continue distilling until no n-butanol distills out. Finally, a small amount of biphenyl is evaporated, and a small amount of viscous solid separates from the water layer in the distillation flask. Add sulfuric acid to the residual liquid to acidify it until the Congo red test paper changes color, and dilute (if necessary) to 150-200 ml. Without separating out the precipitate, heat the mixture to boiling while continuing to stir. After a short time, the crystals will completely melt and become a heavy, insoluble brown oil layer. Pour the aqueous layer through the pleated filter paper.

Extract the oil layer with several 20 ml portions of boiling water, filter the extract while it is hot, and combine it with the original water layer. After cooling, white needle-shaped phenylboronic acid crystallizes. The product weighs 14-17 grams (50-60%) after drying and is no longer refined. The melting point is measured with a capillary tube at 214-216°C (corrected). 1-2 grams of impure product can also be recovered from the mother liquor. When preparing larger quantities and using more concentrated Grignard reagent solutions, the yield will be lower (42-47%).

Main reference materials

[1] Dictionary of Organic Compounds

[2] Xu Dan, Chu Liangyin. Research progress on the application of phenylboronic acid and its derivatives in the fields of medicine and chemical industry [J]. Progress in Chemical Engineering, 2006, 25(9): 1045-1048.

[3] Wei Wenlong, Chen Wenwen, Li Xing, et al. Research progress on Suzuki coupling reaction of halogenated aromatic hydrocarbons and phenylboronic acid[J]. Chemical Engineering Times, 2011, 25(4): 31-34.