Anti-Leishmanial activity of homo- and heteroleptic bismuth(III) carboxylates

A Second Wind for Inorganic APIs: Leishmanicidal and Antileukemic Activity of Hydrated Bismuth Oxide Nanoparticles

American cutaneous leishmaniasis is a disease caused by protozoa of the genus Leishmania. Currently, meglumine antimoniate is the first-choice treatment for the disease. The limited efficacy and high toxicity of the drug results in the necessity to search for new active principles. Nanotechnology is gaining importance in the field, since it can provide better efficacy and lower toxicity of the drugs. The present study aimed to synthesize, characterize, and evaluate the in vitro leishmanicidal and antileukemic activity of bismuth nanoparticles (BiNPs). Promastigotes and amastigotes of L. (V.) guyanensis and L. (L.) amazonensis were exposed to BiNPs. The efficacy of the nanoparticles was determined by measurement of the parasite viability and the percentage of infected cells, while the cytotoxicity was characterized by the colorimetry. BiNPs did not induce cytotoxicity in murine peritoneal macrophages and showed better efficacy in inhibiting promastigotes (IC50 < 0.46 nM) and amastigotes of L. (L.) amazonensis. This is the first report on the leishmanicidal activity of Bi-based materials against L. (V.) guayanensis. BiNPs demonstrated significant cytotoxic activity against K562 and HL60 cells at all evaluated concentrations. While the nanoparticles also showed some cytotoxicity towards non-cancerous Vero cells, the effect was much lower compared to that on cancer cells. Treatment with BiNPs also had a significant effect on inhibiting and reducing colony formation in HL60 cells. These results indicate that bismuth nanoparticles have the potential for an inhibitory effect on the clonal expansion of cancer cells.

Susceptibility of Leishmania to novel pentavalent organometallics: Investigating impact on DNA and membrane integrity in antimony(III)-sensitive and -resistant strains

The aim the present study was to investigate the impact of novel pentavalent organobismuth and organoantimony complexes on membrane integrity and their interaction with DNA, activity against Sb(III)-sensitive and -resistant Leishmania strains and toxicity in mammalian peritoneal macrophages. Ph3M(L)2 type complexes were synthesized, where M = Sb(V) or Bi(V) and L = deprotonated 3-(dimethylamino)benzoic acid or 2-acetylbenzoic acid. Both organobismuth(V) and organoantimony(V) complexes exhibited efficacy at micromolar concentrations against Leishmania amazonensis and L. infantum but only the later ones demonstrated biocompatibility. Ph3Sb(L1)2 and Ph3Bi(L1)2 demonstrated distinct susceptibility profiles compared to inorganic Sb(III)-resistant strains of MRPA-overexpressing L. amazonensis and AQP1-mutated L. guyanensis. These complexes were able to permeate the cell membrane and interact with the Leishmania DNA, suggesting that this effect may contribute to the parasite growth inhibition via apoptosis. Taken altogether, our data substantiate the notion of a distinct mechanism of uptake pathway and action in Leishmania for these organometallic complexes, distinguishing them from the conventional inorganic antimonial drugs.

Bioactive Bismuth Compounds: Is Their Toxicity a Barrier to Therapeutic Use?

Bismuth compounds are considered relatively non-toxic, with their low solubility in aqueous solutions (e.g., biological fluids) being the major contributing factor to this property. Bismuth derivatives are widely used for the treatment of peptic ulcers, functional dyspepsia, and chronic gastritis. Moreover, the properties of bismuth compounds have also been extensively explored in two main fields of action: antimicrobial and anticancer. Despite the clinical interest of bismuth-based drugs, several side effects have also been reported. In fact, excessive acute ingestion of bismuth, or abuse for an extended period of time, can lead to toxicity. However, evidence has demonstrated that the discontinuation of these compounds usually reverses their toxic effects. Notwithstanding, the continuously growing use of bismuth products suggests that it is indeed part of our environment and our daily lives, which urges a more in-depth review and investigation into its possible undesired activities. Therefore, this review aims to update the pharmaco-toxicological properties of bismuth compounds. A special focus will be given to in vitro, in vivo, and clinical studies exploring their toxicity.

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.

Aryl bismuth phosphinates [BiAr2(O(O)PRR’)]: structure-activity relationships for antibacterial activity and cytotoxicity

To study and evaluate the structure-activity relationships in di-aryl bismuth phosphinates on antibacterial activity and cytotoxicity a series of complexes containing ortho-methoxyphenyl, meta-methoxyphenyl, meta-tolyl and para-tolyl aryl groups; [Bi(o-MeOPh)2(O(O)P(H)Ph)]n 1,...

Leishmania tarentolae novel responses to Bi3+-doped strontium aluminum oxyfluorides

Novel therapeutics for the treatment of leishmaniasis are of interest as the disease not only is becoming more prevalent, but drug resistance is increasing in certain regions of the world. Reported here is the use of Bi3+-doped strontium aluminum oxyfluoride phosphors and protease inhibitors to test in vitro inhibitory activity against cultured promastigote Leishmania tarentolae and effects on L. tarentolae secreted acid phosphatase (SAP) activity. Cell viability did not significantly decrease in the presence of 50 μM anti-perovskite compounds, implying limited cytotoxicity. Yet SAP activity did increase in the cell free preparations with time in the presence of strontium compounds. Of interest was the observation that cell free SAP activity did not increase in the presence of protease inhibitors with or without added strontium compounds. Since secreted proteases may play a role in the maturation of Leishmania SAP and thus be involved with parasite-host infection establishment, this is in further need of evaluation. Nitric oxide production on day 4 post-addition of the strontium compounds was evaluated and showed an approximately 50% decrease in NO production in the presence of two test compounds relative to DMSO control cells. This is the first report of anti-perovskite compound inhibition of NO production by Leishmania.

Impact of structural changes in heteroleptic bismuth phosphinates on their antibacterial activity in Bi-nanocellulose composites

To study and evaluate the effect of ligand choice and distribution in bismuth phosphinates on toxicity and antibacterial activity, a series of novel diphenyl mono-phosphinato bismuth complexes, [BiPh2(O(O[double bond, length as m-dash])P(H)Ph)] 1, [BiPh2(O(O[double bond, length as m-dash])PPh2)] 2, [BiPh2(O(O[double bond, length as m-dash])PMe2)] 3 and [BiPh2(O(O[double bond, length as m-dash])P(p-MeOPh)2)] 4, were synthesised, characterised and structurally authenticated by X-ray crystallography. Evaluation of their antibacterial activity towards Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), vancomycin-resistant Enterococci (VRE), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) showed all four mono-phosphinato bismuth complexes to be highly active. However, unlike their less soluble bis-phosphinato analogues, they displayed an increased level of toxicity towards mammalian cells (COS-7, human and murine fibroblasts), where it was shown the complexes disrupt cellular membranes leading to cytotoxicity. The mono-phosphinato bismuth complexes were used to produce antibacterial nanocellulose composites. Leaching studies showed that complex 1 had the highest levels of leaching, at 15% of the total available bismuth when the composite was soaked in water. The aqueous leachates of 1 were bacteriostatic towards MRSA and VRE at concentrations between 4.0 and 4.6 μM, while being bactericidal towards E. coli above 2.8 μM. At similar concentrations the complex showed toxicity towards human fibroblast cells, with cell viability reduced to 2% (1, 2.4 μM). The possibility to control leaching of the bismuth complexes from cellulose composites through structural changes is evidence for their potential application in antibacterial surfaces and materials.

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.

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.

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.

Impact of substituents on the crystal structures and anti-leishmanial activity of new homoleptic Bi(iii) dithiocarbamates

Anti-leishmanial activity of six structurally characterised new functionalised homoleptic Bi(iii) dithiocarbamate complexes having monomeric, dimeric and rare polymeric structures has been explored.

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.

Comparative stability, toxicity and anti-leishmanial activity of triphenyl antimony(v) and bismuth(v) α-hydroxy carboxylato complexes

Organometallic bismuth(v) and antimony(v) α-hydroxy carboxylato complexes, [MPh₃(O₂CR(OH))₂] and [MPh₃(O₂CR(O))], have been synthesised, characterised and their activity towards Leishmania promastigotes and amastigotes, and human fibroblast cells, assessed and compared.

Structural influences on the activity of bismuth(III) indole-carboxylato complexes towards Helicobacter pylori and Leishmania

Seven new bismuth(III) complexes derived from indole-carboxylic acids have been synthesised: five are homoleptic; [Bi(IAA)₃] B1, [Bi(IPA)₃] B2, [Bi(IBA)₃] B3, [Bi(MICA)₃] B4, [Bi(IGA)₃] B6, and two are heteroleptic [BiPh(MICA)₂] B5 (where IAA-H=2-(1H-indol-3-yl)acetic acid, IPA-H=3-(1H-indol-3-yl)propanoic acid, IBA-H=4-(1H-indol-3-yl)butanoic acid, IGA-H=2-(1H-indol-3-yl)-2-oxoacetic acid, and MICA-H=1-methyl-1H-indole-3-carboxylic acid). All complexes were fully characterised by elemental analysis, infrared and mass-spectroscopy, and nuclear magnetic resonance (¹H, ¹³C) spectroscopy. Complex [BiPh(IGA)₂] B7 is structurally authenticated by X-ray crystallography as a dimer in the solid-state. The in-vitro anti-bacterial activity of the indole-carboxylic acids and their bismuth(III) complexes was assessed against Helicobacter pylori. While the acids were non-toxic at <100μgmL^-1, all the bismuth compounds showed an MIC of 6.25μgmL^-1, indicating that the anti-bacterial activity is insensitive to the degree of substitution at the Bi(III) centre or the composition of the indole-carboxylate ligands. All compounds were further tested for their anti-parasitic activity against Leishmania major and for their toxicity towards mammalian cells. From the anti-parasitic studies, it was found that the heteroleptic bismuth(III) complexes are the most active, with B5 and B7 showing comparable activity to Amphotericin B, without any toxicity towards the mammalian cells at their effective concentration.

Bismuth⋯π arene versus bismuth⋯halide coordination in heterocyclic diorganobismuth(iii) compounds with transannular N→Bi interaction

The hypervalent diorganobismuth(iii) halides of type [RCH₂N(CH₂C₆H₄)₂]BiX, (R = Ph, Bz, and MeO) show a strong tendency to associate either by Bi⋯X or by Bi⋯π arene secondary interactions.

Stability and toxicity of tris-tolyl bismuth(v) dicarboxylates and their biological activity towards Leishmania major

A series of tris-tolylbismuth(v) dicarboxylates, [Bi(Tol)₃(O₂CR)₂], were synthesised, characterised and evaluated againstLeishmania majorparasites demonstrating good selectivity towards promastigotes but with more moderate success against amastigotes.

Current and potential applications of bismuth-based drugs

: Bismuth compounds have been used extensively as medicines and in particular for the treatment of gastrointestinal ailments. In addition to bismuth's well known gastroprotective effects and efficacy in treating H. pylori infection it also has broad anti-microbial, anti-leishmanial and anti-cancer properties. Aspects of the biological chemistry of bismuth are discussed and biomolecular targets associated with bismuth treatment are highlighted. This review strives to provide the reader with an up to date account of bismuth-based drugs currently used to treat patients and discuss potential medicinal applications of bismuth drugs with reference to recent developments in the literature. Ultimately this review aims to encourage original contributions to this exciting and important field.

Activity of antifungal organobismuth(III) compounds derived from alkyl aryl ketones against S. cerevisiae: comparison with a heterocyclic bismuth scaffold consisting of a diphenyl sulfone

A series of hypervalent organobismuth(III) compounds derived from alkyl aryl ketones [XBi(5-R'C₆H₃-2-COR)(Ar)] was synthesized to investigate the effect of the compounds’ structural features on their antifungal activity against the yeast Saccharomyces cerevisiae. In contrast to bismuth heterocycles [XBi(5-RC₆H₃-2-SO₂C₆H₄-1'-)] derived from diphenyl sulfones, a systematic quantitative structure-activity relationship study was possible. The activity depended on the Ar group and increased for heavier X atoms, whereas lengthening the alkyl chain (R) or introducing a substituent (R') reduced the activity. IBi(C₆H₄-2-COCH₃)(4-FC₆H₄) was the most active. Its activity was superior to that of the related acyclic analogues ClBi[C₆H₄-2-CH₂N(CH₃)₂](Ar) and ClBi(C₆H₄-2-SO₂tert-Bu)(Ar) and also comparable to that of heterocyclic ClBi(C₆H₄-2-SO₂C₆H₄-1'-), which was the most active compound in our previous studies. Density function theory calculations suggested that hypervalent bismuthanes undergo nucleophilic addition with a biomolecule at the bismuth atom to give an intermediate ate complex. For higher antifungal activity, adjusting the lipophilicity-hydrophilicity balance, modeling the three-dimensional molecular structure around the bismuth atom, and stabilizing the ate complex appear to be more important than tuning the Lewis acidity at the bismuth atom.

Novel triphenylantimony(V) and triphenylbismuth(V) complexes with benzoic acid derivatives: structural characterization, in vitro antileishmanial and antibacterial activities and cytotoxicity against macrophages

Two novel organoantimony(V) and two organobismuth(V) complexes of the type ML₂ were synthesized, with L = acetylsalicylic acid (HL1) or 3-acetoxybenzoic acid (HL2) and M = triphenylantimony(V) (M1) or triphenylbismuth(V) (M2). Complexes, [M1(L1)₂] (1), [M1(L2)₂]∙CHCl₃ (2), [M2(L1)₂], (3) and [M2(L2)₂] (4), were characterized by elemental analysis, IR and NMR. Crystal structures of triphenylantimony(V) dicarboxylate complexes 1 and 2 were determined by single crystal X-ray diffraction. Structural analyses revealed that 1 and 2 adopt five-coordinated extremely distorted trigonal bipyramidal geometries, binding with three phenyl groups in the equatorial position and two deprotonated organic ligands (L) in the axial sites. The metal complexes, their metal salts and ligands were evaluated in vitro for their activities against Leishmania infantum and amazonensis promastigotes and Staphylococcus aureus and Pseudomonas aeruginosa bacteria. Both the metal complexes showed antileishmanial and antibacterial activities but the bismuth complexes were the most active. Intriguingly, complexation of organobismuth(V) salt reduced its activity against Leishmania, but increased it against bacteria. In vitro cytotoxic test of these complexes against murine macrophages showed that antimony(V) complexes were the least toxic. Considering the selectivity indexes, organoantimony(V) complexes emerge as the most promising antileishmanial agents and organobismuth(V) complex 3 as the best antibacterial agent.

Stability and toxicity of heteroleptic organometallic Bi(v) complexes towards Leishmania major

A series of organometallic bismuth(v) dicarboxylates, [BiPh₃(O₂CR′)₂], were synthesised and evaluated for their anti-leishmanial activity. The complexes are effective against parasite promastigotes (0.6–2.5 μM), but prone to slow reductive decomposition.

Bismuth(III) β-thioxoketonates as antibiotics against Helicobacter pylori and as anti-leishmanial agents

Nine different β-thioxoketones of general formula R(1)C(=O)CH2C(=S)R(2) (R(1) = C6H5, R(2) = C6H5L1; R(1) = C6H5, R(2) = p-CF3C6H4L2; R(1) = p-MeOC6H4, R(2) = C6H5L3; R(1) = p-MeOC6H4, R(2) = p-CF3C6H4L4; R(1) = C5H4N, R(2) = C6H5L5; R(1) = p-IC6H4, R(2) = C6H5L6; R(1) = C6H5, R(2) = p-IC6H4L7; R(1) = C6H5, R(2) = C10H7L8 and R(1) = CH3, R(2) = C6H5L9) and their tris-substituted bismuth(III) complexes having the general formula [Bi{R(1)C(=O)CHC(=S)R(2)}3] were synthesised and fully characterised. The solid state structure of [Bi{C5H4NC(=O)CHC(=S)C6H5}3] B5 was determined by crystallography and revealed that the three β-thioxoketonato ligands are bound to bismuth(III) centre in a bidentate fashion through O and S atoms. The bismuth(III) complexes and the corresponding thioxoketones were assessed for their activity against H. pylori. All of the bismuth(III) complexes were highly active against H. pylori having a MIC of greater than or equal to 3.125 μg mL(-1), while the free acids were essentially not toxic to the bacteria. The anti-leishmanial activity of all the bismuth(III) β-thioxoketonates and the corresponding free acids were assessed against L. major promastigotes. The toxicity towards human fibroblast cells was also assessed. All of the free β-thioxoketones were selectively toxic to the L. major promastigotes displaying some potential as anti-leishmanial agents. Among these [C6H5C(=O)CH2C(=S)C6H5] L1 and [C5H4NC(=O)CH2C(=S)C6H5] L5 showed comparable activity to that of Amphotericin B, killing about 80% of the L. major promastigotes at a concentration of 25 μM (6.0 μg mL(-1)). The bismuth(III) β-thioxoketonate complexes were toxic to both the L. major promastigotes and fibroblast cells at high concentrations, but gave no improvement in anti-leishmanial activity over the free β-thioxoketones.

Cytotoxicity and In Vitro Antileishmanial Activity of Antimony (V), Bismuth (V), and Tin (IV) Complexes of Lapachol

Leishmania amazonensis is the etiologic agent of the cutaneous and diffuse leishmaniasis often associated with drug resistance. Lapachol [2-hydroxy-3-(3′-methyl-2-butenyl)-1,4-naphthoquinone] displays a wide range of antimicrobial properties against many pathogens. In this study, using the classic microscopic in vitro model, we have analyzed the effects of a series of lapachol and chlorides complexes with antimony (V), bismuth (V), and tin (IV) against L. amazonensis. All seven compounds exhibited antileishmanial activity, but most of the antimony (V) and bismuth (V) complexes were toxic against human HepG2 cells and murine macrophages. The best IC₅₀ values (0.17 ± 0.03 and 0.10 ± 0.11 μg/mL) were observed for Tin (IV) complexes (3) [(Lp)(Ph₃Sn)] and (6) (Ph₃SnCl₂), respectively. Their selective indexes (SIs) were 70.65 and 120.35 for HepG2 cells, respectively. However, while analyzing murine macrophages, the SI decreased. Those compounds were moderately toxic for HepG2 cells and toxic for murine macrophages, still underlying the need of chemical modification in this class of compounds.

Main-Group Medicinal Chemistry Including Li and Bi*

Main-group element compounds were among the first developed in the modern era as pharmaceutical preparations for the treatment of a wide variety of human ailments; it is now recognized that many of these elements exist in traditional medicine of many societies, for example, arsenic. The use of main-group element compounds in contemporary medicine continues for the treatment of, for example, depression (Li), stomach ulcers (Bi), cancer (As and Ga), and leishmaniasis (Sb). Not surprisingly, new compounds of these elements, and other main-group elements, continue to be investigated for their potential use in new therapies. In this chapter, the use of main-group elements as therapeutic agents is outlined and also, where understood, comments on biological targets and mechanisms of action. Further, key advances in new potential applications of main-group element compounds in medicine are evaluated.

Bismuth compounds in medicinal chemistry

In recent years, the chemical potential of bismuth and bismuth compounds has been actively exploited. Bismuth salts are known for their low toxicity, making them potential valuable reagents for large-scale synthesis, which becomes more obvious when dealing with products such as active pharmaceutical ingredients or synthetic intermediates. Conversely, bismuth compounds have been widely used in medicine. After extensive use in the treatments of syphilis and other bacterial infections before the advent of modern antibiotics, bismuth compounds remain important for the treatment of several gastrointestinal disorders and also exhibit antimicrobial properties and cytotoxic activity, among others. This review updates relevant advances in the past few years, concerning the application of bismuth reagents and catalysts in innovative synthetic processes for the preparation of compounds of medicinal interest, as well as the preparation, biological evaluation and potential medicinal uses of bismuth compounds.

Improved antileishmanial activity of Dppz through complexation with antimony(III) and bismuth(III): investigation of the role of the metal

Two novel trivalent antimony(III) and bismuth(III) complexes with the nitrogen-donor heterocyclic ligand dipyrido[3,2-a:2',3'-c]phenazine (dppz) were synthesized and characterized as [Sb(dppz)Cl₃]∙H₂O∙CH₃OH and [Bi(dppz)Cl₃]. The crystal structure of Sb(III) complex was determined by X-ray crystallography. These complexes were evaluated for their activity against the promastigote form of Sb(III)-sensitive and -resistant Leishmania infantum chagasi and Leishmania amazonensis strains. Both complexes were more effective than dppz alone in inhibiting the growth of Leishmania promastigotes and were at least 77 and 2,400 times more active than potassium antimonyl tartrate in Sb(III)-sensitive and -resistant Leishmania, respectively. The cytotoxicity of dppz and its complexes against mouse peritoneal macrophages occurred at dppz concentrations at least 6-fold greater than those found to be active against Leishmania promastigotes.To investigate the role of the metal in the improved antileishmanial activity of dppz, the activity of the Sb(III) complex was compared between the Sb-resistant mutants and their respective parental sensitive strains. The lack of cross-resistance to the Sb(III)-dppz complex together with the much lower activity of antimonyl tartrate, SbCl₃ and BiCl₃ strongly support the model that the metal is not active by itself but improves the activity of dppz through complexation.

Recent advances in bioinorganic chemistry of bismuth

Bismuth has been used in medicine for over two centuries for the treatment of various diseases, in particular for gastrointestinal disorders, owing to its antimicrobial activity. Recent structural characterization of bismuth drugs provides an insight into assembly and pharmacokinetic pathway of the drugs. Mining potential protein targets inside the pathogen via metallomic/metalloproteomic approach and further characterization on the interactions of bismuth drugs with these targets laid foundation in understanding the mechanism of action of bismuth drugs. Such studies would be beneficial in rational design of new potential drugs.