Boron-Containing Peptidomimetics - A Novel Class of Selective Anti-tubercular Drugs

Visible-Light-Driven Decarboxylative Borylation: Rapid Access to α- and β-Amino-boronamides

In this study, we described a two-step process involving an efficient visible-light-induced decarboxylative borylation of α- and β-amino redox-active esters with bis(catecholato)diboron, followed by transamination with 1,8-diaminonapthalene (DANH2). A series of boronamides were obtained in moderate to excellent yields in this one-pot procedure. The photochemical process proved to be very efficient even when conducted under flow conditions with shorter reaction durations and scalable synthesis of DAN boronates.

Asymmetric Synthesis of β-Aminoboronates via Copper-Catalyzed Reductive Coupling of Vinyl Boronates with Imines

We report a copper-catalyzed asymmetric reductive coupling of vinyl boronates with imines, which directly access enantiomerically enriched β-aminoalkylboronates. Stereoselective addition of the in situ generated chiral α-borylalkyl copper to N-phosphinoyl imines provided target products in good yields with high diastereo- and enantioselectivity. Vinyl boronate with methylated acenaphthoquinone as a boron ligand was essential to efficiently spawn asymmetric products, and organic transformations of the boron moiety, along with the easily removable N-protecting group, proved their synthetic utility.

Remote Site-Selective Asymmetric Protoboration of Unactivated Alkenes Enabled by Bimetallic Relay Catalysis

A remote C(sp³ )-H bond asymmetric borylation of unactivated alkenes was achieved by bimetallic relay catalysis. The reaction proceeded through reversible and consecutive β-H elimination/olefin insertion promoted by CoH species generated in situ, followed by copper-catalyzed asymmetric protoboration. The use of this synergistic Co/Cu catalysis protocol allowed the enantioselective protoboration of various unactivated terminal alkenes and internal alkenes, as well as an unrefined mixture of olefin isomers, at the distal less-reactive β-position to a functional group, leading to chiral organoboronates.

A tandem process for the synthesis of β-aminoboronic acids from aziridines with haloamine intermediates

An unprecedented synthetic strategy is devised to generate β-aminoboronic acids from aziridines via a sequential process involving 1,2-iodoamine formation and radical borylation under light irradiation. A variety of aziridines including multiply substituted aziridines have been successfully employed as synthetic precursors, expanding their synthetic utility compared to previous methods. Mechanistic studies suggest that the boron source plays a unique role in the borylation step, and in the formation of haloamine intermediates.

The Boron Advantage: The Evolution and Diversification of Boron’s Applications in Medicinal Chemistry

In this review, the history of boron’s early use in drugs, and the history of the use of boron functional groups in medicinal chemistry applications are discussed. This includes diazaborines, boronic acids, benzoxaboroles, boron clusters, and carboranes. Furthermore, critical developments from these functional groups are highlighted along with recent developments, which exemplify potential prospects. Lastly, the application of boron in the form of a prodrug, softdrug, and as a nanocarrier are discussed to showcase boron’s emergence into new and exciting fields. Overall, we emphasize the evolution of organoboron therapeutic agents as privileged structures in medicinal chemistry and outline the impact that boron has had on drug discovery and development.

Copper-Catalyzed Ring-Opening Reactions of Alkyl Aziridines with B2pin2: Experimental and Computational Studies

The possibility to form new C-B bonds with aziridines using diboron derivatives continues to be a particularly challenging field in view of the direct preparation of functionalized β-aminoboronates, which are important compounds in drug discovery, being a bioisostere of β-aminoacids. We now report experimental and computational data that allows the individuation of the structural requisites and of reaction conditions necessary to open alkyl aziridines using bis(pinacolate)diboron (B₂pin₂) in a regioselective nucleophilic addition reaction under copper catalysis.

Boron-based hybrids as novel scaffolds for the development of drugs with neuroprotective properties

Novel boron-based compounds (BBCs) were synthesized and evaluated as potential candidates for the development of novel drugs against Alzheimer's disease (AD). The neuroprotective profile of novel BBCs was evaluated using Aβ1-42-treated-SH-SY5Y cells while their antioxidant activity was evaluated by total antioxidant capacity (TAC) and total oxidative status (TOS) assays. Results showed that BLA (a novel boron-based hybrid containing an antioxidant portion) inhibited cell death induced by Aβ1-42-exposure in differentiated SH-SY5Y cells, resulting in an increase in cell viability by 25-33% (MTT assay) and by 63-71% (LDH assay) in a concentration range of 25-100 μM. Antioxidant assays demonstrated a good capability of BLA to counteract the oxidative status. Moreover, BLA possessed a significant ability to inhibit acetylcholinesterase (AChE) (22.96% at 50 μM), an enzyme whose enzymatic activity is increased in AD patients. In the present work, absorption and distribution properties of boron-based hybrids were predicted using Pre-ADMET software. In vitro preliminary results suggested that boron-based hybrids could be new structural scaffolds for the development of novel drugs for the management of AD.

Iridium-Catalyzed Regio- and Enantioselective Borylation of Unbiased Methylene C(sp3 )-H Bonds at the Position β to a Nitrogen Center

Reported herein is the pyrazole-directed iridium-catalyzed enantioselective borylation of unbiased methylene C-H bonds at the position β to a nitrogen center. The combination of a chiral bidentate boryl ligand, iridium precursor, and pyrazole directing group was responsible for the high regio- and enantioselectivity observed. The method tolerated a vast array of functional groups to afford the corresponding C(sp³ )-H functionalization products with good to excellent enantioselectivity.

Palladium-Catalyzed Regioselective and Stereospecific Ring-Opening Cross-Coupling of Aziridines: Experimental and Computational Studies

Aziridines, i.e., the smallest saturated N-heterocycles, serve as useful building blocks in synthetic organic chemistry. Because of the release of the large ring strain energy accommodated in the small ring, (ca. 27 kcal/mol), aziridines undergo ring-opening reactions with a variety of nucleophiles. Therefore, among the synthetic reactions utilizing aziridines, regioselective ring-opening substitutions of aziridines with nucleophiles, such as heteroatomic nucleophiles (e.g., amines, alcohols, and thiols) and carbonaceous nucleophiles (e.g., carbanions, organometallic reagents, and electron-rich arenes), constitute a useful synthetic methodology to synthesize biologically relevant β-functionalized alkylamines. However, the regioselection in such traditional ring-opening substitutions of aziridines is highly dependent on the substrate combination, and stereochemical control is challenging to achieve, especially in the case of Lewis acid-promoted variants. Therefore, the development of robust catalytic ring-opening functionalization methods that enable precise prediction of regioselectivity and stereochemistry is desirable. In this direction, our group focused on the highly regioselective and stereospecific nature of the stoichiometric oxidative addition elementary step of 2-substituted aziridines into Pd(0) complexes in an S_N2 fashion. In conjunction with the recent advancements in transition-metal-catalyzed cross-coupling reactions of alkyl pseudohalides containing a C(sp³)-Q (Q = O, N, S, etc.) bond, aziridines can be used as nonclassical alkyl pseudohalides in regioselective and stereospecific cross-couplings.In this Account, starting from the background of transition-metal-catalyzed ring-opening functionalization of aziridines, our contributions to the palladium-catalyzed regioselective and stereoinvertive cross-couplings of aziridines with organoboron reagents to form C(sp³)-C, C(sp³)-B, and C(sp³)-Si bonds have been compiled. The developed methods allow the syntheses of medicinally important amine compounds, e.g., enantioenriched β-phenethylamines, β-amino acids, and their boron and silyl surrogates, from readily available enantiopure aziridine substrates. Notably, the regioselectivity of the ring opening can be switched by appropriate selection of the catalyst (i.e., Pd/NHC vs Pd/PR₃ systems). Computational studies rationalized the detailed mechanisms of the full catalytic cycle and the regioselectivity and stereospecificity of the reactions. The computational results suggested that the interactions operating between the Pd catalyst and aziridine substrate play important roles in determining the regioselection of the aziridine ring-opening event (i.e., oxidative addition). Also, the computational results rationalized the role of water molecules in promoting the transmetalation step through the formation of a Pd-hydroxide active intermediate. This Account evidences the benefits of synergistic collaborations between experimental and computational methods in developing novel transition-metal-catalyzed cross-coupling reactions.

Repurposed drug candidates for antituberculosis therapy

Antibiotics have been a key part of clinical treatments for more than 70 years. Long-term use of antimicrobial treatments has led to the development of severe bacterial resistance, which has become increasingly serious due to antibiotic abuse, resulting in the treatment of bacterial infections becoming challenging. The repurposing of approved drugs presents a promising strategy to address current bottlenecks in the development of novel antibacterial agents. Drug repurposing is a cost-effective emerging strategy, which aims to treat resistant infectious diseases by identifying known drugs with predicted efficacy for diseases other than the target disease. This strategy has potential in the treatment of tuberculosis (TB), particularly drug-resistant TB. In recent years, a panel of drugs approved for clinical use or clinical trials, such as linezolid, vancomycin and celecoxib, have been found to have anti-TB activities. However, the utility of drug repurposing is limited by the number of candidate compounds and their low activities. The low activities of repurposed drugs have slowed the development of a drug-repurposing strategy for anti-TB drugs. The present review discusses progress in the discovery of new anti-TB agents through drug repurposing since 2014. We also discuss the challenges faced and analyze the innovative ways that are being used to overcome these difficulties. This review may provide a useful guide for researchers in the field of drug repurposing.

Synthesis of biologically active boron-containing compounds

Boron-containing compounds which possess unique and attractive properties have received increasing attention from the pharmaceutical industry and academia recently. They have shown interesting and useful biological activities, including antibacterial, antifungal, antiparasitic, antiviral, and anti-inflammatory activities. In this review, the synthetic strategies for various boron-containing compounds, including peptidyl boronic acids, benzoxaboroles, benzoxaborines, benzodiazaborines, amine carboxyboranes, and amine cyanoboranes are summarized. Representative structures of each structural class and recently developed biologically active boron-containing compounds are used as examples in this review.

Morin P, Westcott SA. Synthesis, characterization, and anticancer properties of iminophosphineplatinum(II) complexes containing boronate esters

Three new iminophosphines containing pinacol-derived boronate esters have been prepared and ligated to dichloridoplatinum(II) fragments. All compounds have been characterized fully, including an X-ray diffraction study carried out for the platinum complex 8, which is derived from 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline. These three new platinum complexes, along with the non-boron containing control, have been examined for their initial cytotoxic properties against two glioma cell lines using the MTT method.

Palladium-catalyzed regioselective and stereo-invertive ring-opening borylation of 2-arylaziridines with bis(pinacolato)diboron: experimental and computational studies

A palladium catalyzed regioselective borylative ring opening reaction of 2-arylaziridines to give β-amino-β-arylethylborates was developed. The reaction reported herein represents the first example of ring-opening borylation of non-vinylic aziridines and direct borylative C(sp3)-N bond cleavage of neutral organic substrates. NMR studies and density functional theory (DFT) calculations suggested that the active intermediate for the reaction is a PdL2 complex [L = P(t-Bu)2Me]. The multi-component artificial force-induced reaction method (MC-AFIR) located the transition states for the regioselectivity-determining aziridine ring opening that proceeds in an SN2 fashion, and explained the selectivity of the reaction. The full catalytic cycle consists of a selectivity-determining aziridine ring opening (oxidative addition), a proton transfer, phosphine ligand dissociation from the catalyst, boron-boron bond cleavage, and reductive elimination. Water is important to the drive the transmetalation step. The calculated overall mechanism and selectivity are consistent with the experimental results.

Coronin 1 trimerization is essential to protect pathogenic mycobacteria within macrophages from lysosomal delivery

Coronin 1 is a member of the evolutionarily conserved coronin protein family. Coronin proteins are characterized by the presence of a central WD repeat and a C-terminal coiled coil that in coronin 1 is responsible for trimerization. Coronin 1 was identified as a host protein protecting intracellularly residing mycobacteria from degradation by activating the Ca(2+)/calcineurin pathway but whether or not trimerization is essential for this function remains unknown. We here show that trimerization is essential to promote mycobacterial survival within macrophages and activate calcineurin. Furthermore, macrophage activation that induces serine-phosphorylation on coronin 1 resulted in coronin 1 monomerization. These results suggest that modulation of coronin 1 oligomerization is an effective way to determine the outcome of a mycobacterial infection in macrophages.

Influence of fluorine substituents on the NMR properties of phenylboronic acids

The paper presents results of a systematic NMR studies on fluorinated phenylboronic acids. All possible derivatives were studied. The experimental (1)H, (13)C, (19)F, (11)B, and (17)O spectral data were compared with the results of theoretical calculations. The relation between the calculated natural bond orbital parameters and spectral data (chemical shifts and coupling constants) is discussed. The first examples of (10)B/(11)B isotopic effect on the (19)F spectra and (4)JFO scalar coupling in organic compounds are reported.

Synthesis and antimicrobial activity of α-aminoboronic-containing peptidomimetics

A library of 175 dipeptidomimetics and tripeptidomimetics containing an α-amino boronic acid or boronate has been synthesized, and the activity toward Mycobacterium tuberculosis, Candida albicans, Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Pseudomonas aeruginosa has been screened. Although there is no clear structure-activity relationship, several compounds exhibit promising activity against different pathogens.