Accelerated click reactions using boronic acids for heterocyclic synthesis in microdroplets

Click chemistry is important for its simplicity and versatility, however, condensation-based click reactions are limited by the general requirement of high temperatures and catalysts. Here, we report accelerated click reactions using boronic acids in microdroplets under ambient conditions without a catalyst. The reaction between 2-formyl phenylboronic acid (2-FPBA) and substituted amines leads to the formation of multi-step click products, including iminoboronates, boroxines, thiazolidines, and diazaborines, depending on the selected amine. The reactions occur during microdroplet flight and are three orders of magnitude faster than the corresponding bulk reactions. MS and NMR spectral analysis confirmed the nature of the products. We suggest that the air-liquid interface of microdroplets serves both as a superacid and as a drying surface, facilitating dehydration by its superacidicity to access these products. We also demonstrate the application of these accelerated reactions as a late-stage functionalization (LSF) tool to access a range of antihistamine drug derivatives.

Formulations with Boric Acid or Aryl-Organoboron Compounds for Treating Diabetic Foot Ulcers

Boron-containing compounds (BCCs) have been proposed for the treatment of diabetes and its complications. Recent studies have reported an improvement in the design and development of pharmaceutical formulations (often gels) containing boric acid applied to the foot ulcers of humans diagnosed with diabetes. The proposed mechanisms of action of boric acid include antimicrobial effects, the modulation of inflammation and metabolism, and the induction of cell differentiation. On the other hand, recent studies have suggested that boronic acids are potent antibacterial and antifungal compounds, effective modulators of inflammation, and inducers of vascular regeneration as well as inducers of healing, and they confer attractive properties such as adhesion, interaction, and the formation of complexes in formulations. Moreover, only a handful of studies conducted in animals have suggested the effective role of some BCCs as potent enhancers of wound healing, including their actions on induced and/or infected wounds in animals with disrupted metabolism. Also, it should be mentioned that no strong interactions between boric acid and the boronic acids present in formulations have been described. The developed combination could act as an additive and complementary therapy in the treatment of diabetic ulcers in humans. Further studies are required to support the hypothesis that this combination acts through diverse mechanisms to improve healing while avoiding or limiting a local or disseminated infection. Furthermore, the safety of BCCs used for foot ulcers should be established, as should the role of these formulations as a complementary therapy in current protocols for treating patients with diabetic foot ulcers.

Expanding the Role of Boron in New Drug Chemotypes: Properties, Chemistry, Pharmaceutical Potential of Hemiboronic Naphthoids

New chemotypes and bioisosteres can open a new chemical space in drug discovery and help meet an urgent demand for novel agents to fight infections and other diseases. With the aim of identifying new boron-containing drug chemotypes, this article details a comprehensive evaluation of the pseudoaromatic hemiboronic naphthoids, benzoxaza- and benzodiazaborines. Relevant physical properties in aqueous media (acidity, solubility, log P, and stability) of prototypic members of four subclasses were determined. Both scaffolds are amenable to common reactions used in drug discovery, such as chemoselective Suzuki-Miyaura, Chan-Lam, and amidation reactions. Small model libraries were prepared to assess the scope of these transformations, and the entire collection was screened for antifungal (Candida albicans) and antibacterial activity (MRSA, Escherichia coli), unveiling promising benzoxazaborines with low micromolar minimum inhibitory concentration values. Select DMPK assays of representative compounds suggest promising drug-like behavior for all four subclasses. Moreover, several drug isosteres were evaluated for anti-inflammatory and anticancer activity as appropriate.

Boron-Containing heterocycles as promising pharmacological agents

The incorporation of the "magic" boron atom has been established as an important new strategy in the field of medicinal chemistry as boron compounds have been shown to form various bonds with their biological targets. Currently, a number of boron-based drugs (e.g. bortezomib, crisaborole, and tavaborole) have been FDA approved and are in the clinic, and several other boron-containing compounds are in clinical trials. Boron-based heterocycles have an incredible potential in the ongoing quest for new therapeutic agents owing to their plethora of biological activities and useful pharmacokinetic profiles. The present perspective is intended to review the pharmacological applications of boron-based heterocycles that have been published. We have classified these compounds into groups exhibiting shared pharmacological activities and discussed their corresponding biological targets focusing mainly on the most potent therapeutic compounds.

Preparation of Cu(II), Ni(II), Ti(IV), VO(IV), and Zn(II) Metal Complexes Derived from Novel vic-Dioxime and Investigation of Their Antioxidant and Antibacterial Activities

In this work, novel vic-dioxime ligand (LH₂ ) containing bound to the N₄ -oxime core moiety and its complexes with Cu(II), Ni(II), Ti(IV), VO(IV), and Zn(II) salts have been studied. The structure of the ligand and its complexes were successfully synthesized and characterized using NMR (¹ H and ¹³ C), LC/MS/MS spectrometer, FT-IR and UV/VIS spectroscopy, melting point, and magnetic susceptibility measurements. Vic-dioxime ligand (LH₂ ) (1) and its metal complexes ([Cu(LH)₂ ] (2), [Ni(LH)₂ ] (3), [Ti(LH)₂ ]Cl₂ (4), [VO(LH)₂ ] (5), and [Zn(LH)₂ ] (6), respectively) were tested for them in-vitro antibacterial and antioxidant activities. According to the metal chelating results of the study, it was determined that compounds (1), (2), (3), and (6) showed very good activity, and especially compound (2), had a stronger metal chelating capacity due to ligand dissociation from the synthesized metal complexes, which then would chelate Fe(II) in the experimental setting. When microorganisms were evaluated in terms of the % viability effect, it was observed that all compounds had activity against C. Albicans and S. Cerevisiae at rates similar to antibiotics.

Boron-containing capsaicinoids

This study reports on the preparation of eight new boron-containing capsaicinoids bearing long aliphatic chains, as an expansion of our previous studies to include tertiary amide derivatives into our substrate scope. Our boron-moiety, a pinacolboronate ester (Bpin) fragment, has been incorporated in two locations: as an aryl substituent of the capsaicinoid produced by the reductive amination of veratraldehyde, or at the terminal end of an aliphatic substituent using an iridium catalyzed hydroboration reaction. We report that most compounds in our series show moderate antimicrobial and cytotoxic activity, surpassing activities noted in our previous study.

Progress in the medicinal chemistry of organoboron compounds

The review aims to draw attention to the latest advances in the organoboron chemistry and therapeutic use of organoboron compounds. The synthetic strategies towards boron-containing compounds with proven in vitro and/or in vivo biological activities, including derivatives of boronic acids, benzoxaboroles, benzoxaborines and benzodiazaborines, are summarized. Approaches to the synthesis of hybrid structures containing an organoboron moiety as one of the pharmacophores are considered, and the effect of this modification on the pharmacological activity of the initial molecules is analyzed. On the basis of analysis of the published data, the most promising areas of research in the field of organoboron compounds are identified, including the latest methods of synthesis, modification and design of effective therapeutic agents.

The bibliography includes 246 references.

Boronic acid based dynamic click chemistry: recent advances and emergent applications

Recently, reversible click reactions have found numerous applications in chemical biology, supramolecular chemistry, and biomedical applications. Boronic acid (BA)-mediated cis-diol conjugation is one of the best-studied reactions among them. An excellent understanding of the chemical properties and biocompatibility of BA-based compounds has inspired the exploration of novel chemistries using boron to fuel emergent sciences. This topical review focuses on the recent progress of iminoboronate and salicylhydroxamic-boronate constituted reversible click chemistries in the past decade. We highlight the mechanism of reversible kinetics and its applications in chemical biology, medicinal chemistry, biomedical devices, and material chemistry. This article also emphasizes the fundamental reactivity of these two conjugate chemistries with assorted nucleophiles at variable pHs, which is of utmost importance to any stimuli-responsive biological and material chemistry explorations.