Methylboronic acid is the simplest organic boronic acid derivative. It is an important intermediate for the preparation of many boronic acid derivatives such as (S) or (R)-2-methyl-CBS-oxazoborane, which has many uses in organic synthesis. Methylboronic acid is a white to light yellow crystal powder with a pKa of 9.97. It is a reagent for various cross-couplings, silylation reactions, and polymerizations.

Methylboronic acid fertilization alleviates boron deficiency symptoms

Boron is an essential plant micronutrient and is a structural component of the cell wall. Its absence results in zero plant growth as boron is involved in all growth processes, including buds, meristems, and roots. In addition, flowering and fruit development are very sensitive to boron availability. This implies that boron deficiency significantly affects crops, fruits, and forest species yield. With the aim of employing a chemical compound similar to BA but not toxic to plants, methylboronic acid (MBA) was chosen based on its innocuous effect in human cells. Methylboronic acid is a boronic acid related to BA in which a methyl group replaces one of the three-hydroxyl groups. We proposed that MBA might work as a boron fertilizer due to the chemical similarity between MBA and BA. In this work, we evaluated the effect of Methylboronic acid on the growth of roots and leaves in Arabidopsis. We show that MBA alleviates boron deficiency in Arabidopsis. In addition, methylboronic acid enhances plant growth and is less toxic at high concentrations compared to BA. Our findings are limited to leaf and root in Arabidopsis, as boron deficiency symptoms were not analyzed in additional tissues such as meristems and flowers.[1]

In Arabidopsis, the boronic acids 4-biphenylboronic acid and 4-phenoxyphenylboronic acid inhibit auxin biosynthesis, reduce endogenous IAA content, and inhibit primary root elongation and lateral root formation. In this work, we report that the boronic acid Methylboronic acid does not act as boron competitor and is instead capable of alleviating boron deficiency and enhancing plant growth while demonstrating lower toxicity compared to the common fertilizer BA. Our findings are restricted to leaves and roots, as we did not evaluate deficiency symptoms in other Arabidopsis tissues such as meristems and flowers. Why does Methylboronic acid not induce boron deficiency like other boronic acids? It is possible that MBA performs a functional role not yet described in plants. Methylation of proteins, DNA, RNA, sugars, and plant hormones is critically important for modulation and regulation of different processes, developmental changes, and cell signalling. For Methylboronic acid to be utilized by plants, it must be transported from the roots to the shoots. Passive diffusion of BA is thought to satisfy plant demand for boron, together with channels of the major intrinsic protein (MIP) family and the BOR family of borate exporters. Whether Methylboronic acid uses the same mechanism of uptake and mobilization as BA will be subject of subsequent research.

In this work, we describe that methylboronic acid (MBA) is capable of alleviating boron deficiency in Arabidopsis. MBA is a boronic acid, but does not naturally occur in soils, necessitating synthesis. Other boronic acids have been described as boron competitors in plants, inhibiting auxin biosynthesis and root development. Methylboronic acid is more water-soluble than BA and delivers the same amount of boron per molecule. We observed that Arabidopsis seedlings grown in the presence of MBA presented higher numbers of lateral roots and greater main root length compared to plants grown in BA. In addition, root hair length and leaf surface area were increased using MBA as a boron fertilizer. Finally, Methylboronic acid was less toxic than BA at high concentrations, producing a slight reduction in the main root length but no decrease in total chlorophyll. Our results open a new opportunity to explore the use of a synthetic form of boron in agriculture, providing a tool for future research for plant nutrition.

Methylboronic acid MIDA ester as an effective additive in electrolyte

Scientists investigated the effectiveness of using methylboronic acid MIDA ester (ADM) as an additive in an electrolyte to enhance the overall electrochemical and material properties of an LNCAO (LiNi0.8Co0.15Al0.05O2) cathode. The cyclic stability of the cathode material measured at 40 °C (@ 0.2 C) showed an enhanced capacity of 144.28 mAh g?1 (@ 100 cycles), a capacity retention of 80%, and a high coulombic efficiency (99.5%), in contrast to these same properties without the electrolyte additive (37.5 mAh g?1,?~?20%, and 90.4%), thus confirming the effectiveness of the additive.[2]

A Fourier transform infrared spectroscopy (FTIR) analysis distinctly showed that the methylboronic acid MIDA ester additive suppressed the EC-Li+ ion coordination (1197 cm?1 and 728 cm?1) in the electrolyte, thereby improving the cyclic performance of the LNCAO cathode. The cathode after 100 charge/discharge cycles revealed that the methylboronic acid MIDA ester-containing system exhibited better surface stability of the grains in the LNCAO cathode, whereas distinct cracks were observed in the system without the ADM in the electrolyte. A transmission electron microscopy (TEM) analysis revealed the presence of a thin, uniform and dense cathode electrolyte interface (CEI) film on the surface of LNCAO cathode. An operando synchrotron X-ray diffraction (XRD) test identified the high structural reversibility of the LNCAO cathode with a CEI layer formed by the methylboronic acid MIDA ester, which effectively maintained the structural stability of the layered material. The additive effectively inhibited the decomposition of electrolyte compositions, as confirmed by X-ray photoelectron spectroscopy (XPS).

Facile deprotection of F-BODIPYs using methylboronic acid

The dipyrrinato framework is a useful ligand for complexation to metals, the most common featuring first-row transition metals and boron. Reported methods for the removal of the –BF2 moiety from F-BODIPYs, i.e. deprotection to yield the parent dipyrrin, have involved the use of alkoxides and strong Br?nstead and Lewis acids. Herein, we report using methylboronic acid to deprotect thirteen F-BODIPYs and an F-aza-BODIPY to generate the corresponding dipyrrins and aza-dipyrrin in quantitative yield. Cognisant that these conditions represent a mild alternative to existing methods for the deprotection of F-BODIPYs, and in light of the fact that the volatility of methylboronic acid renders work-up facile, we investigated the scope of the reaction conditions. Treatment of 4,4-difluoro-8-phenyl-4-bora-3a,4a-diaza-s-indacene with 5 equiv. methylboronic acid at room temperature. The removal of the –BF2 unit using methylboronic acid was effective for F-BODIPYs bearing unsubstituted positions about the pyrrolic core (entry 6), as well as for unsymmetrical variants (entry 7).[3]

Similarly, the dipyrrin 2j was isolated in quantitative yield upon treatment of the corresponding F-BODIPY with methylboronic acid, thereby demonstrating tolerance of the hydroxy and trifluoromethyl functionalities within these electron-poor constructs. Further demonstration of the ability of methylboronic acid to deprotect F-BODIPYs bearing aryl substituents involved isolation of the two triphenyl-substituted dipyrrins. Attempts to reduce the equivalencies of the Lewis acid were briefly explored, resulting in the observation that 2d could be generated in quantitative yield upon treatment of the corresponding F-BODIPY with just 1 equiv. methylboronic acid. However, this achievement did not extend to the deprotection of F-BODIPYs appended with meso-aryl substituents. Despite the successful deprotection of thirteen F-BODIPYs and one F-aza-BODIPY using 5 equiv. methylboronic acid, the bromo-substituted F-BODIPY reacted sluggishly to result in decomposition. Equally unsuccessful were attempts to use methylboronic acid to remove the –BF2 unit from F-BODIPYs bearing carboxylate- or azido- functionality around the dipyrrolic core.

In conclusion, scientists have developed a high yielding and mild method for the deprotection of F-BODIPYs through the use of volatile methylboronic acid using 5% TFA and CH2Cl2 as solvent. The reaction is performed at room temperature, tolerates substrates bearing a range of substituents around the F-BODIPY framework, and requires only a facile work-up procedure in order to isolate quantitative yields of the dipyrrin as either an HBr salt or a free-base

References

[1]Duran C, Arce-Johnson P, Aquea F. Methylboronic acid fertilization alleviates boron deficiency symptoms in Arabidopsis thaliana. Planta. 2018 Jul;248(1):221-229.

[2]Chen BX, Brahma S, Chen YQ, Huang PC, Chang CC, Huang JL. Methylboronic acid MIDA ester (ADM) as an effective additive in electrolyte to improve cathode electrolyte interlayer performance of LiNi0.8Co0.15Al0.05O2 electrode. Sci Rep. 2023 Jun 20;13(1):10025.

[3]Smith CD, Thompson A. Facile deprotection of F-BODIPYs using methylboronic acid. RSC Adv. 2020 Jun 25;10(41):24273-24279.