Homoleptic and Heteroleptic Bismuth(III) Thiazole-Thiolates and the Influence of Ring Substitution on Their Antibacterial and Antileishmanial Activity

Hinokitiol potentiates antimicrobial activity of bismuth drugs: a combination therapy for overcoming antimicrobial resistance

Antimicrobial resistance (AMR) poses a significant global health threat, rendering many infections untreatable. To combat AMR, repurposing approved drugs has emerged as a cost-effective strategy. Bismuth drugs, when combined with antibiotics, have been proven to be effective against Helicobacter pylori, including antibiotic-resistant strains. However, bismuth drugs alone exhibit limited antimicrobial activity against a narrow spectrum of pathogens. Therefore, a novel approach to enhance the efficacy and broaden the antimicrobial spectrum of bismuth drugs is highly desirable. Herein, we show that a naturally occurring monoterpenoid, hinokitiol, could potentiate the antimicrobial activity of bismuth drugs. We demonstrate a strong synergy between hinokitiol and colloidal bismuth subcitrate (CBS) against various Gram-positive and Gram-negative bacterial strains, including methicillin-resistant Staphylococcus aureus (MRSA). Moreover, the combination of hinokitiol and CBS exhibits anti-biofilm activity by preventing biofilm formation and eliminating S. aureus persister cells. Importantly, the combination therapy demonstrates promising antimicrobial efficacy in murine infection models including skin wound, gastrointestinal and blood infections. Mechanistic studies reveal that hinokitiol enhances bismuth ion (Bi(iii)) accumulation and reduces intracellular iron levels. By using thermal proteome profiling combined with dynamic quantitative proteomics analysis, we demonstrate that the bismuth-hinokitiol combination propagated the bismuth binding and interfered with ribosome synthesis, the glycolysis process, impaired bacterial cell wall synthesis and pathogenesis in MRSA. Our finding highlights the potential of combinatorial hinokitiol and bismuth drugs in the fight against AMR.

Facile synthesis and antifungal evaluation of hypervalent organoantimony(III) and organobismuth(III) thioates with tridentate C,N,C-coordinating ligands

In the present work, a series of organometallic thioates bearing a 5,6,7,12-tetrahydrodibenzo[c,f][1,5]azastibocine or -azabismocine framework were synthesized through the cross-coupling reactions of the corresponding halide precursors with thiols and disulfides at room temperature. The former transformation can be achieved under additive-free conditions, and mild dithiothreitol (DTT) is the only additive in the latter. Both methods feature simple operation, a broad substrate scope, and good reaction yields. Antifungal assays showed that the synthesized organobismuth(III) thioates possess significantly higher antibiotic activity against Candida albicans than clinical fluconazole, while the inhibitory effects of Sb-sulfenylated products are low to negligible. Furthermore, the antibiofilm potential of such Bi-S bond-containing compounds was discovered as well.

Fusing Bismuth and Mercaptocarboranes: Design and Biological Evaluation of Low-Toxicity Antimicrobial Thiolato Complexes

This study proposes an innovative strategy to enhance the pharmacophore model of antimicrobial bismuth thiolato complex drugs by substituting hydrocarbon ligand structures with boron clusters, particularly icosahedral closo-dicarbadodecaborane (C2B10H12, carboranes). The hetero- and homoleptic mercaptocarborane complexes BiPh2L (1) and BiL3 (2) (L=9-S-1,2-C2B10H11) were prepared from 9-mercaptocarborane (HL) and triphenylbismuth. Comprehensive characterization using NMR, IR, MS, and XRD techniques confirmed their successful synthesis. Evaluation of antimicrobial activity in a liquid broth microdilution assay demonstrated micromolar to submicromolar minimum inhibitory concentrations (MIC) suggesting high effectiveness against S. aureus and limited efficacy against E. coli. This study highlights the potential of boron-containing bismuth complexes as promising antimicrobial agents, especially targeting Gram-positive bacteria, thus contributing to the advancement of novel therapeutic approaches.

Current Development of Thiazole-Containing Compounds as Potential Antibacterials against Methicillin-Resistant Staphylococcus aureus

The emergence of multi-drug-resistant bacteria is threatening to human health and life around the world. In particular, methicillin-resistant Staphylococcus aureus (MRSA) causes fatal injuries to human beings and serious economic losses to animal husbandry due to its easy transmission and difficult treatment. Currently, the development of novel, highly effective, and low-toxicity antimicrobials is important to combat MRSA infections. Thiazole-containing compounds with good biological activity are widely used in clinical practice, and appropriate structural modifications make it possible to develop new antimicrobials. Here, we review thiazole-containing compounds and their antibacterial effects against MRSA reported in the past two decades and discuss their structure-activity relationships as well as the corresponding antimicrobial mechanisms. Some thiazole-containing compounds exhibit potent antibacterial efficacy in vitro and in vivo after appropriate structural modifications and could be used as antibacterial candidates. This Review provides insights into the development of thiazole-containing compounds as antimicrobials to combat MRSA infections.

Biological Activities of Bismuth Compounds: An Overview of the New Findings and the Old Challenges Not Yet Overcome

Bismuth-based drugs have been used primarily to treat ulcers caused by Helicobacter pylori and other gastrointestinal ailments. Combined with antibiotics, these drugs also possess synergistic activity, making them ideal for multiple therapy regimens and overcoming bacterial resistance. Compounds based on bismuth have a low cost, are safe for human use, and some of them are also effective against tumoral cells, leishmaniasis, fungi, and viruses. However, these compounds have limited bioavailability in physiological environments. As a result, there is a growing interest in developing new bismuth compounds and approaches to overcome this challenge. Considering the beneficial properties of bismuth and the importance of discovering new drugs, this review focused on the last decade's updates involving bismuth compounds, especially those with potent activity and low toxicity, desirable characteristics for developing new drugs. In addition, bismuth-based compounds with dual activity were also highlighted, as well as their modes of action and structure-activity relationship, among other relevant discoveries. In this way, we hope this review provides a fertile ground for rationalizing new bismuth-based drugs.

Formation of sandwich and multidecker complexes between O2 and alkali/alkaline earth metals: A DFT study

Abstract: Feasibility of formation of sandwich and multidecker complexes between O2 molecules and alkali/alkaline earth metal has been analyzed in the light of density functional theory (DFT). High value of...

Medicinal chemistry and biomedical applications of bismuth-based compounds and nanoparticles

Bismuth as a relatively non-toxic and inexpensive metal with exceptional properties has numerous biomedical applications. Bismuth-based compounds are used extensively as medicines for the treatment of gastrointestinal disorders including dyspepsia, gastric ulcers and H. pylori infections. Recently, its medicinal application was further extended to potential treatments of viral infection, multidrug resistant microbial infections, cancer and also imaging, drug delivery and biosensing. In this review we have highlighted the unique chemistry and biological chemistry of bismuth-209 as a prelude to sections covering the unique antibacterial activity of bismuth including a description of research undertaken to date to elucidate key molecular mechanisms of action against H. pylori, the development of novel compounds to treat infection from microbes beyond H. pylori and the significant role bismuth compounds can play as resistance breakers. Furthermore we have provided an account of the potential therapeutic application of bismuth-213 in targeted alpha therapy as well as a summary of the biomedical applications of bismuth-based nanoparticles and composites. Ultimately this review aims to provide the state of the art, highlight the untapped biomedical potential of bismuth and encourage original contributions to this exciting and important field.

Bismuth(III) Flavonolates: The Impact of Structural Diversity on Antibacterial Activity, Mammalian Cell Viability and Cellular Uptake

A series of homoleptic and heteroleptic bismuth(III) flavonolate complexes derived from six flavonols of varying substitution have been synthesised and structurally characterised. The complexes were evaluated for antibacterial activity towards several problematic Gram-positive (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE)) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The cell viability of COS-7 (monkey kidney) cells treated with the bismuth flavonolates was also studied to determine the effect of the complexes on mammalian cells. The heteroleptic complexes [BiPh(L)₂ ] (in which L=flavonolate) showed good antibacterial activity towards all of the bacteria but reduced COS-7 cell viability in a concentration-dependent manner. The homoleptic complexes [Bi(L)₃ ] exhibited activity towards the Gram-positive bacteria and showed low toxicity towards the mammalian cell line. Bismuth uptake studies in VRE and COS-7 cells treated with the bismuth flavonolate complexes indicated that Bi accumulation is influenced by both the substitution of the flavonolate ligands and the degree of substitution at the bismuth centre.

Is Bismuth Really the "Green" Metal? Exploring the Antimicrobial Activity and Cytotoxicity of Organobismuth Thiolate Complexes

Antimicrobial resistance is becoming an ever-increasing threat for human health. Metal complexes and, in particular, those that incorporate bismuth offer an attractive alternative to the typically used organic compounds to which bacteria are often able to develop resistance determinants. Herein we report the synthesis, characterization, and biological evaluation of a series of homo- and heteroleptic bismuth(III) thiolates incorporating either one (BiPh₂L), two (BiPhL₂), or three (BiL₃) sulfur-containing azole ligands where LH = tetrazolethiols or triazolethiols (thiones). Despite bismuth typically being considered a nontoxic heavy metal, we demonstrate that the environment surrounding the metal center has a clear influence on the safety of bismuth-containing complexes. In particular, heteroleptic thiolate complexes (BiPh₂L and BiPhL₂) display strong antibacterial activity yet are also nonselectively cytotoxic to mammalian cells. Interestingly, the homoleptic thiolate complexes (BiL₃) were shown to be completely inactive toward both bacterial and mammalian cells. Further biological analysis of the complexes revealed the first insights into the biological mode of action of these particular bismuth thiolates. Scanning electron microscopy images of methicillin-resistant Staphylococcus aureus (MRSA) cells have revealed that the cell membrane is the likely target site of action for bismuth thiolates against bacterial cells. This points toward a nonspecific mode of action that is likely to contribute to the poor selectivity's demonstrated by the bismuth thiolate complexes in vitro. Uptake studies suggest that reduced cellular uptake could explain the marked difference in activity between the homo- and heteroleptic complexes.

Bismuth(III) Thiophosphinates: Understanding How a Small Atomic Change Influences Antibacterial Activity and Mammalian Cell Viability

Diphenylphosphinothioic acid (HSP(=O)Ph2) and diphenylphosphinodithioic acid (HSP(=S)Ph2) have been used to synthesise four BiIII complexes: 1 [Bi(SP(=O)Ph2)3], 2 [BiPh(SP(=O)Ph2)2], 3 [BiPh2(SP(=O)Ph2)], and 4 [Bi(SP(=S)Ph2)3], using BiPh3 and [Bi(OtBu)3] as bismuth sources. The complexes have been characterised by NMR spectroscopy, mass spectrometry, infrared spectroscopy, powder X-ray diffraction, and singe crystal X-ray crystallography (2–4). Biological studies indicated that despite complexes 2 and 3 reducing mammalian cell viability, their antibacterial activity provides a good degree of selectivity towards both Gram positive and Gram negative bacterial strains. The minimum inhibitory concentrations for complexes 2 and 3 are in the range of 0.52–5.5µM towards the bacteria tested. Homoleptic complexes 1 and 4 were generally less active towards both bacterial and mammalian cells.

Intramolecular Metal⋅⋅⋅π-Arene Interactions in Neutral and Cationic Main Group Compounds

The role of intramolecular metal⋅⋅⋅π-arene interactions has been investigated in the solid-state structures of a series of main group compounds supported by the bulky amide ligands, [N(^tBu Ar^≠ )(SiR₃ )]^- (^tBu Ar^≠ =2,6-(CHPh₂ )₂ -4-tBuC₆ H₂ , R=Me, Ph). The lithium and potassium amide salts showed different patterns of solvation and demonstrated that the SiPh₃ substituent is able to be involved in stabilizing the electrophilic metal. These group 1 metal compounds served as ligand transfer reagents to access a series of bismuth(III) halides. Chloride extraction from Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl₂ using AlCl₃ afforded the 1:1 salt [Bi(N{^tBu Ar^≠ }{SiPh₃ })Cl][AlCl₄ ]. This was accompanied by a significant rearrangement of the stabilizing π-arene contacts in the solid-state. Attempted preparation of the corresponding tetraphenylborate salt resulted in phenyl-transfer and generation of the neutral Bi(N{^tBu Ar^≠ }{SiPh₃ })(Ph)Cl.

Recent Research Trends on Bismuth Compounds in Cancer Chemoand Radiotherapy

Background:

Application of coordination chemistry in nanotechnology is a rapidly developing research field in medicine. Bismuth complexes have been widely used in biomedicine with satisfactory therapeutic effects, mostly in Helicobacter pylori eradication, but also as potential antimicrobial and anti-leishmanial agents. Additionally, in recent years, application of bismuth-based compounds as potent anticancer drugs has been studied extensively.

Methods:

Search for data connected with recent trends on bismuth compounds in cancer chemo- and radiotherapy was carried out using web-based literature searching tools such as ScienceDirect, Springer, Royal Society of Chemistry, American Chemical Society and Wiley. Pertinent literature is covered up to 2016.

Results:

In this review, based on 213 papers, we highlighted a number of current problems connected with: (i) characterization of bismuth complexes with selected thiosemicarbazone, hydrazone, and dithiocarbamate classes of ligands as potential chemotherapeutics. Literature results derived from 50 papers show that almost all bismuth compounds inhibit growth and proliferation of breast, colon, ovarian, lung, and other tumours; (ii) pioneering research on application of bismuth-based nanoparticles and nanodots for radiosensitization. Results show great promise for improvement in therapeutic efficacy of ionizing radiation in advanced radiotherapy (described in 36 papers); and (iii) research challenges in using bismuth radionuclides in targeted radioimmunotherapy, connected with choice of adequate radionuclide, targeting vector, proper bifunctional ligand and problems with 213Bi recoil daughters toxicity (derived from 92 papers).

Conclusion:

This review presents recent research trends on bismuth compounds in cancer chemo- and radiotherapy, suggesting directions for future research.

Evaluation of dispersion type metal···π arene interaction in arylbismuth compounds - an experimental and theoretical study

The dispersion type Bi···π arene interaction is one of the important structural features in the assembly process of arylbismuth compounds. Several triarylbismuth compounds and polymorphs are discussed and compared based on the analysis of single crystal X-ray diffraction data and computational studies. First, the crystal structures of polymorphs of Ph3Bi (1) are described emphasizing on the description of London dispersion type bismuth···π arene interactions and other van der Waals interactions in the solid state and the effect of it on polymorphism. For comparison we have chosen the substituted arylbismuth compounds (C6H4-CH═CH2-4)3Bi (2), (C6H4-OMe-4)3Bi (3), (C6H3-t-Bu2-3,5)3Bi (4) and (C6H3-t-Bu2-3,5)2BiCl (5). The structural analyses revealed that only two of them show London dispersion type bismuth···π arene interactions. One of them is the styryl derivative 2, for which two polymorphs were isolated. Polymorph 2a crystallizes in the orthorhombic space group P212121, while polymorph 2b exhibits the monoclinic space group P21/c. The general structure of 2a is similar to the monoclinic C2/c modification of Ph3Bi (1a), which leads to the formation of zig-zag Bi-arenecentroid ribbons formed as a result of bismuth···π arene interactions and π···π intermolecular contacts. In the crystal structures of the polymorph 2b as well as for 4 bismuth···π arene interactions are not observed, but both compounds revealed C-HPh···π intermolecular contacts, as likewise observed in all of the three described polymorphs of Ph3Bi. For compound 3 intermolecular contacts as a result of coordination of the methoxy group to neighboring bismuth atoms are observed overruling Bi···π arene contacts. Compound 5 shows a combination of donor acceptor Bi···Cl and Bi···π arene interactions, resulting in an intermolecular pincer-type coordination at the bismuth atom. A detailed analysis of three polymorphs of Ph3Bi (1), which were chosen as model systems, at the DFT-D level of theory supported by DLPNO-CCSD(T) calculations reveals how van der Waals interactions between different structural features balance in order to stabilize molecular arrangements present in the crystal structure. Furthermore, the computational results allow to group this class of compounds into the range of heavy main group element compounds which have been characterized as dispersion energy donors in previous work.

Bismuth Phosphinates in Bi-Nanocellulose Composites and their Efficacy towards Multi-Drug Resistant Bacteria

A series of poorly soluble phenyl bis-phosphinato bismuth(III) complexes [BiPh(OP(=O)R¹ R² )₂ ] (R¹ =R² =Ph; R¹ =R² =p-OMePh; R¹ =R² =m-NO₂ Ph; R¹ =Ph, R² =H; R¹ =R² =Me) have been synthesised and characterised, and shown to have effective antibacterial activity against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). The bismuth complexes were incorporated into microfibrillated (nano-) cellulose generating a bismuth-cellulose composite as paper sheets. Antibacterial evaluation indicates that the Bi-cellulose materials have analogous or greater activity against Gram positive bacteria when compared with commercial silver based additives: silver sulfadiazine loaded at 0.43 wt % into nanocellulose produces a 10 mm zone of inhibition on the surface of agar plates containing S. aureus whereas [BiPh(OP(=O)Ph₂ )₂ ] loaded at 0.34 wt % produces an 18 mm zone of inhibition. These phenyl bis-phosphinato bismuth(III) complexes show potential to be applied in materials in healthcare facilities, to inhibit the growth of bacteria capable of causing serious disease.

Do bismuth complexes hold promise as antileishmanial drugs?

Even after 70 years, pentavalent antimonials sodium stibogluconate and meglumine antimoniate remain the most important and cost-effective antileishmanial drugs. However, the drugs cannot be delivered orally and treatment involves intravascular or intramuscular injections for 28 days under strict medical monitoring due to the toxicity of Sb(III). The main alternatives, amphotericin B, pentamidine and miltefosine, are expensive and not without their own problems. Bismuth sits below antimony in the periodic table and is considered to be relatively nontoxic to humans while being capable of providing powerful antimicrobial activity. This review describes recent efforts into developing antileishmanial Bi(III) and Bi(V) drugs, which may resemble Sb analogs in effect and mode-of-action while providing lower mammalian cell toxicity and opportunities of oral delivery. Within the last 10 years, various studies concerning bismuth-based compounds as potential antileishmanial agents have been published. This review seeks to summarize the relevant studies and draw a conclusion as to whether bismuth complexes have the potential to be effective drugs.

The role of dispersion type metal⋯π interaction in the enantiotropic phase transition of two polymorphs of tris-(thienyl)bismuthine

Bi(2-C₄H₃S)₃ shows an enantiotropic phase transition that is dominated by London dispersion forces. DFT calculations on model compounds were carried out in order to investigate the competition between Bi⋯S and Bi⋯π heteroarene interaction.