Semisynthesis and Biological Evaluation of Xanthone Amphiphilics as Selective, Highly Potent Antifungal Agents to Combat Fungal Resistance

Synthesis and antibacterial medicinal evaluation of carbothioamido hydrazonyl thiazolylquinolone with multitargeting antimicrobial potential to combat increasingly global resistance

The global microbial resistance is a serious threat to human health, and multitargeting compounds are considered to be promising to combat microbial resistance. In this work, a series of new thiazolylquinolones with multitargeting antimicrobial potential were developed through multi-step reactions using triethoxymethane and substituted anilines as start materials. Their structures were confirmed by 1H NMR, 13C NMR and HRMS spectra. Antimicrobial evaluation revealed that some of the target compounds could effectively inhibit microbial growth. Especially, carbothioamido hydrazonyl aminothiazolyl quinolone 8a showed strong inhibitory activity toward drug-resistant Staphylococcus aureus with MIC value of 0.0047 mM, which was 5-fold more active than that of norfloxacin. The highly active compound 8a exhibited negligible hemolysis, no significant toxicity in vitro and in vivo, low drug resistance, as well as rapidly bactericidal effects, which suggested its favorable druggability. Furthermore, compound 8a was able to effectively disrupt the integrity of the bacterial membrane, intercalate into DNA and inhibit the activity of topoisomerase IV, suggesting multitargeting mechanism of action. Compound 8a could form hydrogen bonds and hydrophobic interactions with DNA-topoisomerase IV complex, indicating the insertion of aminothiazolyl moiety was beneficial to improve antibacterial efficiency. These findings indicated that the active carbothioamido hydrazonyl aminothiazolyl quinolone 8a as a chemical therapeutic candidate demonstrated immense potential to tackle drug-resistant bacterial infections.

Targeting yeast topoisomerase II by imidazo and triazoloacridinone derivatives resulting in their antifungal activity

Fungal pathogens are considered as serious factors for deadly diseases and are a case of medical concern. Invasive fungal infections also complicate the clinical course of COVID-19, leading to a significant increase in mortality. Furthermore, fungal strains' multidrug resistance has increased the demand for antifungals with a different mechanism of action. The present study aimed to identify antifungal compounds targeting yeast topoisomerase II (yTOPOII) derived from well-known human topoisomerase II (hTOPOII) poisons C-1305 and C-1311. Two sets of derivatives: triazoloacridinones (IKE1-8) and imidazoacridinones (IKE9-14) were synthetized and evaluated with a specific emphasis on the molecular mechanism of action. Our results indicated that their effectiveness as enzyme inhibitors was not solely due to intercalation ability but also as a result of influence on catalytic activity by the formation of covalent complexes between plasmid DNA and yTOPOII. Lysine conjunction increased the strength of the compound's interaction with DNA and improved penetration into the fungal cells. Triazoloacridinone derivatives in contrast to starting compound C-1305 exhibited moderate antifungal activity and at least twice lower cytotoxicity. Importantly, compounds (IKE5-8) were not substrates for multidrug ABC transporters whereas a derivative conjugated with lysine (IKE7), showed the ability to overcome C. glabrata fluconazole-resistance (MIC 32-64 µg mL-1).

Benzamidine Conjugation Converts Expelled Potential Active Agents into Antifungals against Drug-Resistant Fungi

Fungal infections present a growing global public health concern, necessitating the development of novel antifungal drugs. However, many potential antifungals, particularly the expelled potential active agents (EPAAs), are often underestimated owing to their limitations in cellular entry or expulsion by efflux pumps. Herein, we identified 68 EPAAs out of 2322 candidates with activity against a Candida albicans efflux pump-deficient strain and no inhibitory activity against the wild-type strain. Using a novel conjugation strategy involving benzamidine (BM) as a mitochondrion-targeting warhead, we successfully converted EPAAs into potent antifungals against various urgent-threat azole-resistantCandida strains. Among the obtained EPAA-BM conjugates, IS-2-BM (11) exhibited excellent antifungal activities and induced negligible drug resistance. Furthermore, IS-2-BM prevented biofilm formation, eradicated mature biofilms, and exhibited excellent therapeutic effects in a murine model of systemic candidiasis. These findings provide a promising strategy for increasing the possibilities of discovering more antifungals.

Recent developments in membrane targeting antifungal agents to mitigate antifungal resistance

Fungal infections cause severe and life-threatening complications especially in immunocompromised individuals. Antifungals targeting cellular machinery and cell membranes including azoles are used in clinical practice to manage topical to systemic fungal infections. However, continuous exposure to clinically used antifungal agents in managing the fungal infections results in the development of multi-drug resistance via adapting different kinds of intrinsic and extrinsic mechanisms. The unique chemical composition of fungal membranes presents attractive targets for antifungal drug discovery as it is difficult for fungal cells to modify the membrane targets for emergence of drug resistance. Here, we discussed available antifungal drugs with their detailed mechanism of action and described different antifungal resistance mechanisms. We further emphasized structure-activity relationship studies of membrane-targeting antifungal agents, and classified membrane-targeting antifungal agents on the basis of their core scaffold with detailed pharmacological properties. This review aims to pique the interest of potential researchers who could explore this interesting and intricate fungal realm.

Isolation and Biological Evaluation of Alfa-Mangostin as Potential Therapeutic Agents against Liver Fibrosis

The increased proliferation and activation of hepatic stellate cells (HSCs) are associated with liver fibrosis development. To date, there are no FDA-approved drugs for the treatment of liver cirrhosis. Augmentation of HSCs apoptosis is one of the resolutions for liver fibrosis. In this study, we extracted α-mangostin (1,3,6-trihydroxy-7-methoxy-2,8-bis(3-methyl-2-butenyl)-9H-xanthen-9-one) from the fruit waste components of mangosteen pericarp. The isolated α-mangostin structure was determined and characterized with nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) and compared with those known compounds. The intracellular signaling pathway activities of α-mangostin on Transforming growth factors-beta 1 (TGF-β1) or Platelet-derived growth factor subunit B (PDGF-BB) induced HSCs activation and were analyzed via Western blot and Real-time Quantitative Polymerase Chain Reaction (Q-PCR). α-Mangostin-induced mitochondrial dysfunction and apoptosis in HSCs were measured by seahorse assay and caspase-dependent cleavage. The in vivo anti-fibrotic effect of α-mangostin was assessed by carbon tetrachloride (CCl4) treatment mouse model. The data showed that α-mangostin treatment inhibited TGF-β1-induced Smad2/3 phosphorylation and alpha-smooth muscle actin (α-SMA) expression in HSCs in a dose-dependent manner. Regarding the PDGF-BB-induced HSCs proliferation signaling pathways, α-mangostin pretreatment suppressed the phosphorylation of extracellular-signal-regulated kinase (ERK) and p38. The activation of caspase-dependent apoptosis and dysfunction of mitochondrial respiration (such as oxygen consumption rate, ATP production, and maximal respiratory capacity) were observed in α-mangostin-treated HSCs. The CCl4-induced liver fibrosis mouse model showed that the administration of α-mangostin significantly decreased the expression of the fibrosis markers (α-SMA, collagen-a2 (col1a2), desmin and matrix metalloproteinase-2 (MMP-2)) as well as attenuated hepatic collagen deposition and liver damage. In conclusion, this study demonstrates that α-mangostin attenuates the progression of liver fibrosis through inhibiting the proliferation of HSCs and triggering apoptosis signals. Thus, α-mangostin may be used as a potential novel therapeutic agent against liver fibrosis.

Synthetic and natural guanidine derivatives as antitumor and antimicrobial agents: A review

Guanidines are fascinating small nitrogen-rich organic compounds, which have been frequently associated with a wide range of biological activities. This is mainly due to their interesting chemical features. For these reasons, for the past decades, researchers have been synthesizing and evaluating guanidine derivatives. In fact, there are currently on the market several guanidine-bearing drugs. Given the broad panoply of pharmacological activities displayed by guanidine compounds, in this review, we chose to focus on antitumor, antibacterial, antiviral, antifungal, and antiprotozoal activities presented by several natural and synthetic guanidine derivatives, which are undergoing preclinical and clinical studies from January 2010 to January 2023. Moreover, we also present guanidine-containing drugs currently in the market for the treatment of cancer and several infectious diseases. In the preclinical and clinical setting, most of the synthesized and natural guanidine derivatives are being evaluated as antitumor and antibacterial agents. Even though DNA is the most known target of this type of compounds, their cytotoxicity also involves several other different mechanisms, such as interference with bacterial cell membranes, reactive oxygen species (ROS) formation, mitochondrial-mediated apoptosis, mediated-Rac1 inhibition, among others. As for the compounds already used as pharmacological drugs, their main application is in the treatment of different types of cancer, such as breast, lung, prostate, and leukemia. Guanidine-containing drugs are also being used for the treatment of bacterial, antiprotozoal, antiviral infections and, recently, have been proposed for the treatment of COVID-19. To conclude, the guanidine group is a privileged scaffold in drug design. Its remarkable cytotoxic activities, especially in the field of oncology, still make it suitable for a deeper investigation to afford more efficient and target-specific drugs.

Synthesis and Molecular Docking Studies of Alkoxy- and Imidazole-Substituted Xanthones as α-Amylase and α-Glucosidase Inhibitors

Current antidiabetic drugs have severe side effects, which may be minimized by new selective molecules that strongly inhibit α-glucosidase and weakly inhibit α-amylase. We have synthesized novel alkoxy-substituted xanthones and imidazole-substituted xanthones and have evaluated them for their in silico and in vitro α-glucosidase and α-amylase inhibition activity. Compounds 6c, 6e, and 9b promoted higher α-glucosidase inhibition (IC₅₀ = 16.0, 12.8, and 4.0 µM, respectively) and lower α-amylase inhibition (IC₅₀ = 76.7, 68.1, and >200 µM, respectively) compared to acarbose (IC₅₀ = 306.7 µM for α-glucosidase and 20.0 µM for α-amylase). Contrarily, derivatives 10c and 10f showed higher α-amylase inhibition (IC₅₀ = 5.4 and 8.7 µM, respectively) and lower α-glucosidase inhibition (IC₅₀ = 232.7 and 145.2 µM, respectively). According to the structure-activity relationship, attaching 4-bromobutoxy or 4'-chlorophenylacetophenone moieties to the 2-hydroxy group of xanthone provides higher α-glucosidase inhibition and lower α-amylase inhibition. In silico studies suggest that these scaffolds are key in the activity and interaction of xanthone derivatives. Enzymatic kinetics studies showed that 6c, 9b, and 10c are mainly mixed inhibitors on α-glucosidase and α-amylase. In addition, drug prediction and ADMET studies support that compounds 6c, 9b, and 10c are candidates with antidiabetic potential.

Amino-Acid-Conjugated Natural Compounds: Aims, Designs and Results

Protein is one of the essential macronutrients required by all living things. The breakdown of protein produces monomers known as amino acids. The concept of conjugating natural compounds with amino acids for therapeutic applications emerged from the fact that amino acids are important building blocks of life and are abundantly available; thus, a greater shift can result in structural modification, since amino acids contain a variety of sidechains. This review discusses the data available on amino acid–natural compound conjugates that were reported with respect to their backgrounds, the synthetic approach and their bioactivity. Several amino acid–natural compound conjugates have shown enhanced pharmacokinetic characteristics, including absorption and distribution properties, reduced toxicity and increased physiological effects. This approach could offer a potentially effective system of drug discovery that can enable the development of pharmacologically active and pharmacokinetically acceptable molecules.

Design and Synthesis of Phenyl Sulfide-Based Cationic Amphiphiles as Membrane-Targeting Antimicrobial Agents against Gram-Positive Pathogens

Due to the emergence of antimicrobial resistance and the lack of new antibacterial agents, it has become urgent to discover and develop new antibacterial agents against multidrug-resistant pathogens. Antimicrobial peptides (AMPs) serve as the first line of defense for the host. In this work, we have designed, synthesized, and biologically evaluated a series of phenyl sulfide derivatives by biomimicking the structural features and biological functions of AMPs. Among these derivatives, the most promising compound 17 exhibited potent antibacterial activity against Gram-positive bacteria (minimum inhibitory concentrations = 0.39-1.56 μg/mL), low hemolytic activity (HC₅₀ > 200 μg/mL), and high membrane selectivity. In addition, 17 can rapidly kill Gram-positive bacteria within 0.5 h through membrane-targeting action and avoid antibiotic resistance. More importantly, 17 showed high in vivo efficacy against Staphylococcus aureus in a murine corneal infection model. Therefore, 17 has great potential as a lead compound for the treatment of Gram-positive bacterial infections.

Guanidine-Containing Antifungal Agents against Human-Relevant Fungal Pathogens (2004-2022)-A Review

The guanidine moiety is typically a highly basic group, and can be found in a wide variety of drugs, such as zanamivir (Relenza) and metformin (Fortamet), as well as in biologically active compounds for numerous disease areas, including central nervous system (CNS) diseases and chemotherapeutics. This review will focus on antifungal agents which contain at least one guanidine group, for the treatment of human-related fungal pathogens, described in the literature between 2004 and 2022. These compounds include small molecules, steroids, polymers, metal complexes, sesquiterpenes, natural products, and polypeptides. It shall be made clear that a diverse range of guanidine-containing derivatives have been published in the literature and have antifungal activity, including efficacy in in vivo experiments.

Design, synthesis, and biological evaluation of tetrahydroquinoline amphiphiles as membrane-targeting antimicrobials against pathogenic bacteria and fungi

The rising prevalence of drug-resistant pathogens is one of the biggest threats to human health. The development of new antibiotics that can overcome drug resistance is in urgent need. Herein, we designed and synthesized a series of amphiphilic tetrahydroquinoline derivatives as small-molecule-based antimicrobial peptidomimetics. Two lead compounds 36 and 52 which contained the tetrahydroquinoline core, hydrophobic alkyl chains (n-nonyl or isoprenyl group), different spacer lengths (n = 4 or 8), and cationic guanidine moiety, showed poor hemolytic activity, low cytotoxicity, and potent broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as fungi. The further biological evaluation revealed that compounds 36 and 52 can kill bacteria and fungi rapidly via membrane-targeting action and avoid drug resistance development. More importantly, compounds 36 and 52 exhibited similarly potent in vivo antimicrobial activities in a murine corneal infection caused by Staphylococcus aureus ATCC29213 or Pseudomonas aeruginosa ATCC9027, as compared to vancomycin or gatifloxacin. These results suggest that compounds 36 and 52 have great potential as new broad-spectrum antimicrobial agents to combat microbial resistance.

Effect of Bis-Dimethylamine Substitution on DNA Binding Property and Cytotoxic Activity of Polyhydroxyxanthone

A bis-dimethylamine substituted xanthone (Xan-2) was obtained by cationic modification of the free C3 and C6 hydroxy groups of 1,3,6-trihydroxyxanthone (Xan-1) which was isolated from Polygala hongkongensis Hemsl.. The results of the spectroscopic analysis, melting profiles, electrophoretic migration, PCR assay and molecular docking indicated that the hydrophobic plane of Xan-1 and Xan-2 could intercalate into the DNA base pairs meanwhile the basic amine alkyl chain of Xan-2 could bind with DNA phosphate framework via electrostatic interaction. Thus, Xan-2 exhibited higher DNA binding affinity than Xan-1. Further study showed that Xan-2 could inhibit the proliferation of HeLa, SGC-7901 and A549 cells effectively by MTT assay and induce apoptosis of HeLa cells as detected by AO/EB staining and flow cytometry assay. Interestingly, Xan-2 exhibited selective cytotoxicity to cells, which was proved by its relatively low inhibitory effect on Raw 264.7 cell. What these studies mean is that disubstituted amine alkyl chains will play an important role in DNA binding property and cytotoxic activity, providing a direction for the development of novel potential antitumor agents.

9-Trifluoromethylxanthenediols: Synthesis and Supramolecular Motifs

The synthesis of four derivatives and the single-crystal X-ray structures of six 9-trifluoromethylxanthenediols (TFXdiols) I-VI are analyzed in this work. These compounds were obtained through superacid-catalyzed condensation of dihydroxybenzenes with 1,1,1-trifluoroacetone or 2,2,2-trifluoroacetophenone. The title molecules have a convex molecular structure due to their three fused rings of the xanthene moiety. We have found that, similar to resorcinol, the configuration of the hydroxyl groups is of great relevance for the crystal packing favoring either interactions above and below their molecular plane or lateral interactions that create layers. Considering that reports of TFXdiols are very scarce, our findings contribute to a better understanding of the molecular conformation and intermolecular interactions in their crystal structures. A similar analysis was extended to a fortuitous cocrystal obtained between 9-trifluoromethyl-9-(4'-fluorophenyl)-xanthenediol and 1,4-dihydroxybenzene, showing that these structures might be used to obtain cocrystals in the future.

Synthesis and antifungal screening of tetramethyl hexahydro-1H-xanthene-1,8(2H)-dione derivatives as potential inhibitors of morphogenesis and biofilm formation in Candida albicans

A series of hexahydro-1H-xanthene-1,8(2H)-dione derivatives were synthesized. All the derivatives were screened for their anti-virulence properties against Candida albicans. In silico studies were performed to corroborate the experimentally observed facts.

Optimization and Evaluation of Novel Antifungal Agents for the Treatment of Fungal Infection

Due to the increased morbidity and mortality by fungal infections and the emergence of severe antifungal resistance, there is an urgent need for new antifungal agents. Here, we screened for antifungal activity in our in-house library through the minimum inhibitory concentration test and derived two hit compounds with moderate antifungal activities. The hit compounds' antifungal activities and drug-like properties were optimized by substituting various aryl ring, alkyl chain, and methyl groups. Among the optimized compounds, 22h was the most promising candidate with good drug-like properties and exhibited potent fast-acting fungicidal antifungal effects against various fungal pathogens and synergistic antifungal activities with some known antifungal drugs. Additionally, 22h was further confirmed to disturb fungal cell wall integrity by activating multiple cell wall integrity pathways. Furthermore, 22h exerted significant antifungal efficacy in both the subcutaneous infection mouse model and ex vivo human nail infection model.

Novel α-Mangostin Derivatives from Mangosteen (Garcinia mangostana L.) Peel Extract with Antioxidant and Anticancer Potential

The mangosteen peels contain biologically active compounds, with antioxidant and anticancer properties. Among these isolated phytochemicals, α-mangostin is one of the most powerful natural antioxidants and anticancer compounds. This study focused on synthesizing novel α-mangostin (α-MG) derivatives at positions of C-3 and C-6 from extracted α-MG of mangosteen peels and investigating antioxidant and anticancer activities. The structures of the synthesized compounds were determined by using MS, 1H-NMR, 13C-NMR, and HPLC. The analysis of the interaction between structure and bioactivity showed that phenol groups on C-3 and C-6 positions play a crucial role in antiproliferative activity to boost both anticancer efficacy and drug-like properties. The antioxidant activity of α-MG and its derivatives were investigated by the DPPH method. Among α-MG derivatives, 1-hydroxy-7-methoxy-2,8-bis(3-methylbut-2-en-1-yl)-9-oxo-9H-xanthene-3,6-diyl bis(2-bromobenzoate) (compound 4) exhibited significant antioxidant property. The in vitro cytotoxicity against various cancer cell lines (HeLa, MCF-7, NCI–H460, and HepG2) was evaluated by the standard sulforhodamine B assay. The anticancer activities (HeLa, MCF-7, NCI–H460, and HepG2) of compound 4 are five to six times higher than those of α-MG and other derivatives. The acetylation at C-3 and C-6 of α-MG by halogen of benzoyl greatly improved cancer cell toxicity. Our results provide new opportunities for further explorations of α-MG derivatives for antioxidant property and promise as drugs in cancer therapy.

Development of Amphiphilic Coumarin Derivatives as Membrane-Active Antimicrobial Agents with Potent In Vivo Efficacy against Gram-Positive Pathogenic Bacteria

Increases in drug-resistant pathogens are becoming a serious detriment to human health. To combat pathogen infections, a new series of amphiphilic coumarin derivatives were designed and synthesized as antimicrobial agents with membrane-targeting action. We herein report a lead compound, 25, that displayed potent antibacterial activity against Gram-positive bacteria, including MRSA. Compound 25 exhibited weak hemolytic activity and low toxicity to mammalian cells and can kill Gram-positive bacteria quickly (within 0.5 h) by directly disrupting the bacterial cell membranes. Additionally, compound 25 demonstrated excellent efficacy in a murine corneal infection caused by Staphylococcus aureus. These results suggest that 25 has great potential to be a potent antimicrobial agent for treating drug-resistant Gram-positive bacterial infections.

Rational Design of Dipicolylamine-Containing Carbazole Amphiphiles Combined with Zn2+ as Potent Broad-Spectrum Antibacterial Agents with a Membrane-Disruptive Mechanism

Antibiotic resistance has become one of the most urgently important problems facing healthcare providers. A novel series of dipicolylamine-containing carbazole amphiphiles with strong Zn²⁺ chelating ability were synthesized, biomimicking cationic antimicrobial peptides. Effective broad-spectrum 16 combined with 12.5 μg/mL Zn²⁺ was identified as the most promising antimicrobial candidate. 16 combined with 12.5 μg/mL Zn²⁺ exhibited excellent antimicrobial activity against both Gram-positive and Gram-negative bacteria (MICs = 0.78-3.125 μg/mL), weak hemolytic activity, and low cytotoxicity. Time-kill kinetics and mechanism studies revealed 16 combined with 12.5 μg/mL Zn²⁺ had rapid bacterial killing properties, as evidenced by disruption of the integrity of bacterial cell membranes, effectively preventing bacterial resistance development. Importantly, 16 combined with 12.5 μg/mL Zn²⁺ showed excellent in vivo efficacy in a murine keratitis model caused by Staphylococcus aureus ATCC29213 or Pseudomonas aeruginosa ATCC9027. Therefore, 16 combined with 12.5 μg/mL Zn²⁺ could be a promising candidate for treating bacterial infections.

Design, Synthesis, and Biological Evaluation of Membrane-Active Bakuchiol Derivatives as Effective Broad-Spectrum Antibacterial Agents

Infections caused by drug-resistant bacteria seriously endanger human health and global public health. Therefore, it is urgent to discover and develop novel antimicrobial agents to combat multidrug-resistant bacteria. In this study, we designed and synthesized a series of new membrane-active bakuchiol derivatives by biomimicking the structure and function of cationic antibacterial peptides. The most promising compound 28 displayed potent antibacterial activity against both Gram-positive bacteria (minimum inhibitory concentration, MIC = 1.56-3.125 μg/mL) and Gram-negative bacteria (MIC = 3.125 μg/mL), very weak hemolytic activity, and low cytotoxicity. Compound 28 had rapid bactericidal properties and avoided bacterial resistance. More importantly, compound 28 showed strong in vivo antibacterial efficacy against Staphylococcus aureus and Pseudomonas aeruginosa in murine corneal infection models. This design strategy is expected to provide an effective solution to the antibiotic crisis.

De Novo Design of Flavonoid-Based Mimetics of Cationic Antimicrobial Peptides: Discovery, Development, and Applications

The alarming rate at which pathogens are developing resistance to conventional antibiotics represents one of the major global challenges to public health care. The prevalence of multidrug-resistant microorganisms is a major impetus for the discovery and development of new antimicrobials. Nature has, to date, been the source of most of the antibiotics discovered and used, including cationic antimicrobial peptides (CAMPs). CAMPs are key components of the innate immune system that are widely found in humans, animals, plants, and microorganisms and that serve as a first line of defense for the host. The attractive features of CAMPs have led to their recognition as potential new antimicrobials. However, they possess several inherent flaws that limit their clinical application including low stability, poor oral bioavailability, poor in vivo efficacy, and a high production cost. To address these issues, small molecule-based peptidomimetic antimicrobials have been designed to biomimic the structural features and biological function of CAMPs. Plant-derived flavonoids (e.g., xanthones and flavones) are active components in traditional herbal medicines and have been reported to contain a variety of significant pharmacological actions including antibacterial, antiviral, antioxidant, and anticancer activities. Over the past decade, we have developed a new chemical strategy to design, discover, and develop xanthone- or flavone-based peptidomimetics and have designed, synthesized, and biologically evaluated a library of approximately 450 new xanthone or flavone derivatives. The designed, structurally diverse compounds can be generally classified into two subfamilies, namely, peptidic and nonpeptidic amphiphilic xanthone or flavone derivatives. In this Account, we describe our efforts on the design, synthesis, biological property evaluation, and mechanism of action model studies of synthetic mimics of CAMPs. The flavonoid compounds are an important component of these rationally designed mimics because they function as hydrophobic aromatic moieties conjugated with different length lipid moieties, behave like an unnatural hydrophobic residue, and provide a rigid scaffold, with the reduced conformational flexibility more likely to provide an active conformation. The mimics can effectively disrupt the integrity of the bacterial membranes. Our endeavors encompass design principles, chemical synthesis, in vitro screening, structural optimization, extensive structural-activity relationship analysis, and a mechanism of action study through biophysical technologies including NMR spectroscopy techniques and computer dynamics simulations, drug resistance assays, in vivo pharmaceutical kinetics (PK) analyses, and in vivo efficacy evaluations of selected promising compounds against drug-resistant bacteria and fungi. Our major contributions to the discovery and development of flavonoid-based mimics as antimicrobials include effectively addressing several limitations associated with CAMPs and have led to promising compounds with a notable potential for further development as new therapeutic antimicrobial agents for the treatment of drug-resistant bacteria- or fungi-induced infections.

The chemistry and biology of guanidine secondary metabolites

Covering: 2017-2019Guanidine natural products isolated from microorganisms, marine invertebrates and terrestrial plants, amphibians and spiders, represented by non-ribosomal peptides, guanidine-bearing polyketides, alkaloids, terpenoids and shikimic acid derived, are the subject of this review. The topics include the discovery of new metabolites, total synthesis of natural guanidine compounds, biological activity and mechanism-of-action, biosynthesis and ecological functions.

A comprehensive overview of the medicinal chemistry of antifungal drugs: perspectives and promise

The emergence of new fungal pathogens makes the development of new antifungal drugs a medical imperative that in recent years motivates the talents of numerous investigators across the world. Understanding not only the structural families of these drugs but also their biological targets provides a rational means for evaluating the merits and selectivity of new agents for fungal pathogens and normal cells. An equally important aspect of modern antifungal drug development takes a balanced look at the problems of drug potency and drug resistance. The future development of new antifungal agents will rest with those who employ synthetic and semisynthetic methodology as well as natural product isolation to tackle these problems and with those who possess a clear understanding of fungal cell architecture and drug resistance mechanisms. This review endeavors to provide an introduction to a growing and increasingly important literature, including coverage of the new developments in medicinal chemistry since 2015, and also endeavors to spark the curiosity of investigators who might enter this fascinatingly complex fungal landscape.

Promising antifungal agents: A minireview

In the recent past, prevalence of life threatening fungal diseases have increased rapidly in immune-compromised cases such as acquired immunodeficiency syndrome (AIDS), cancer, organ transplant etc. Side by side, the appearance of drug resistance to the presently available antifungal therapeutics is on a rapid rise. It has become a top priority for the academia and pharmaceutical industries to develop new antifungal agents able to combat this resistance, and at the same time, possess potential broad spectrum of activity and minimum toxicity. An understanding of the pharmacological interactions between antifungal agents and their targets offers opportunities for design of new therapeutics. This review discusses the various methodology of drug design, structure activity relationships (SARs), and mode of action of variety of new antifungal agents.

Applying an innovative biodegradable self-assembly nanomicelles to deliver α-mangostin for improving anti-melanoma activity

α-Mangostin (αM), a traditional natural product with promising application of treating a series of diseases, was limited use in clinical due to its hydrophobicity. Herein, MPEG-PCL nanomicelles were used to embed the αM for resolving hydrophobicity and improving the anti-melanoma effect of the αM. The anti-melanoma activity and potential mechanisms of biodegradable αM/MPEG-PCL nanomicelles were investigated. The αM/MPEG-PCL nanomicelles possessed a stronger effect on anti-melanoma compared to the free αM both in vitro and in vivo with a low cytotoxicity in non-tumor cell lines. In the research of mechanisms, the αM/MPEG-PCL nanomicelles inhibited the proliferation of melanoma cell, induced apoptosis via both apoptosis pathways of intrinsic and exogenous in vitro, as well as suppressed tumor growth and restrained angiogenesis in vivo, which implied that the αM/MPEG-PCL nanomicelles have potential application as a novel chemotherapeutic agent in melanoma therapy.

Efflux pump-mediated resistance to antifungal compounds can be prevented by conjugation with triphenylphosphonium cation

Antifungal resistance due to upregulation of efflux pumps is prevalent in clinical Candida isolates. Potential efflux pump substrates (PEPSs), which are active against strains deficient in efflux pumps but inactive against wild-type strains, are usually missed in routine antifungal screening. Here we present a method for identification of PEPSs, and show that conjugation with mitochondria-targeting triphenylphosphonium cation (TPP⁺) can enhance or restore the compounds’ antifungal activity. The screening method involves co-culturing a wild-type C. albicans strain and a Cdr efflux pump-deficient strain, labelled with different fluorescent proteins. We identify several PEPSs from a library of natural terpenes, and restore their antifungal activity against wild-type and azole-resistant C. albicans by conjugation with TPP⁺. The most active conjugate (IS-2-Pi-TPP) kills C. albicans cells, prevents biofilm formation and eliminates preformed biofilms, without inducing significant resistance. The antifungal activity is accompanied by mitochondrial dysfunction and increased levels of intracellular reactive oxygen species. In addition, IS-2-Pi-TPP is effective against C. albicans in a mouse model of skin infection.

Antifungal resistance due to upregulation of efflux pumps is common in Candida albicans. Here, the authors show that conjugation with mitochondria-targeting triphenylphosphonium cation can enhance or restore the antifungal activity of potential efflux pump substrates.

Taib AZ, Mohd Noor N, Mohd Said MI, Abu Bakar M, Mackeen MM. From the Front or Back Door? Quantitative analysis of direct and indirect extractions of α-mangostin from mangosteen (Garcinia mangostana)

The pulp and pericarp of mangosteen (Garcinia mangostana) fruit are popular food, beverage and health products whereby 60% of the fruit consist of the pericarp. The major metabolite in the previously neglected or less economically significant part of the fruit, the pericarp, is the prenylated xanthone α-mangostin. This highly bioactive secondary metabolite is typically isolated using solvent extraction methods that involve large volumes of halogenated solvents either via direct or indirect extraction. In this study, we compared the quantities of α-mangostin extracted using three different extraction methods based on the environmentally friendly solvents methanol and ethyl acetate. The three solvent extractions methods used were direct extractions from methanol (DM) and ethyl acetate (DEA) as well as indirect extraction of ethyl acetate obtained via solvent partitioning from an initial methanol extract (IEA). Our results showed that direct extraction afforded similar and higher quantities of α-mangostin than indirect extraction (DM: 318 mg; DEA: 305 mg; IEA: 209 mg per 5 g total dried pericarp). Therefore, we suggest that the commonly used method of indirect solvent extraction using halogenated solvents for the isolation of α-mangostin is replaced by single solvent direct extraction using the environmentally friendly solvents methanol or ethyl acetate.