Design, synthesis, and biological evaluation of multiple F-18 S1PR1 radiotracers in rodent and nonhuman primate.

Here we report our design and synthesis of 28 new fluorine-containing compounds as potential F-18 radiotracers for CNS imaging of sphingosine-1-phosphate receptor 1 (S1PR1), and determination of their in vitro binding potency and selectivity toward S1PR1 over other S1PR subtypes. Nine potent and selective compounds, 7c&d, 9a&c, 12b, 15b, and 18a-c with IC50 values ranging from 0.6-12.3 nM for S1PR1 and weak binding toward S1PR2, 3, 4, and 5, were further 18F-radiolabeled to produce [18F]7c&d, [18F]9a&c, [18F]12b, [18F]15b, and [18F]18a-c. Multi-step F-18 radiochemistry procedures were investigated for radiosynthesis of [18F]7c&d and [18F]9a&c, and the presumed intermediates were synthesized and authenticated by analytic HPLC. We then performed nonhuman primate (NHP) PET brain imaging studies for eight radiotracers: [18F]7c&d, [18F]9a, [18F]12b, [18F]15b, and [18F]18a-c. Three radiotracers, [18F]7c, [18F]7d, and [18F]15b, had high NHP brain uptake with standardized uptake values (SUVs) at 2 h post-injection of 2.42, 2.84, and 2.00, respectively, and good brain retention. Our ex vivo biodistribution study in rats confirmed [18F]7d had a high brain uptake with no in vivo defluorination. Radiometabolic analysis of [18F]7c and [18F]7d in rat plasma and brain samples found that [18F]7c has a more favorable metabolic profile than [18F]7d. However, the trend of increased brain uptake precludes [18F]7c as a suitable PET radiotracer for imaging S1PR1 in the brain. Further structural optmization is warranted to identify a highly S1PR1-specific radiotracer with rapid brain uptake kinetics.

Thiazolyl hydrazineylidenyl indolones as unique potential multitargeting broad-spectrum antimicrobial agents.

The emergence of pathogenic and drug-resistant microorganisms seriously threatens public safety. This work constructed a unique type of thiazolyl hydrazineylidenyl indolones (THIs) to combat global microbial multidrug-resistance. Bioactive evaluation discovered that some target THIs displayed much superior antimicrobial efficacy than clinical chloromycetin, norfloxacin, cefdinir or fluconazole against the tested strains. Eminently, butyl THI 6c displayed a broad antimicrobial spectrum with low MICs of 0.25-1 µg/mL. The highly active THI 6c not only showed low cytotoxicity and hemolysis, rapidly bactericidal ability, good antibiofilm activity and promising pharmacokinetic properties, but also could significantly impede the development of bacterial resistance. Preliminary exploration of antibacterial mechanism revealed that THI 6c could effectively penetrate the cell membrane of MRSA and embed DNA to form 6c‒DNA supramolecular complex and thus hinder DNA replication. Moreover, THI 6c could reduce cell metabolic activity, which might be attributed to the fact that THI 6c could target the pyruvate kinase of MRSA and interfere with the function of the enzyme. These results provided powerful information for further developing thiazolyl hydrazineylidenyl indolones as new broad-spectrum antimicrobial agents.

Identification of Novel Antifungal Skeleton of Hydroxyethyl Naphthalimides with Synergistic Potential for Chemical and Dynamic Treatments.

The invasion of pathogenic fungi poses nonnegligible threats to the human health and agricultural industry. This work exploited a family of hydroxyethyl naphthalimides as novel antifungal species with synergistic potential of chemical and dynamic treatment to combat the fungal resistance. These prepared naphthalimides showed better antifungal potency than fluconazole towards some tested fungi including Aspergillus fumigatus, Candida tropicalis and Candida parapsilosis 22019. Especially, thioether benzimidazole derivative 7f with excellent anti-Candida tropicalis efficacy (MIC = 4 µg/mL) possessed low cytotoxicity, safe hemolysis level and less susceptibility to induce resistance. Biochemical interactions displayed that 7f could form a supramolecular complex with DNA to block DNA replication, and constitute a biosupermolecule with cytochrome P450 reductase (CPR) from Candida tropicalis to hinder CPR biological function. Additionally, 7f presented strong lipase affinity, which facilitated its permeation into cell membrane. Moreover, 7f with dynamic antifungal potency promoted the production and accumulation of reactive oxygen species (ROS) in cells, which destroyed the antioxidant defence system, led to oxidative stress with lipid peroxidation, loss of glutathione, membrane dysfunction and metabolic inactivation, and eventually caused cell death. The chemical and dynamic antifungal synergistic effect initiated by hydroxyethyl naphthalimides was a reasonable treatment window for prospective development.

Discovery of novel phenylhydrazone-based oxindole-thiolazoles as potent antibacterial agents toward Pseudomonas aeruginosa.

With the soaring of bacterial infection and drug resistance, it is imperative to exploit new efficient antibacterial agents. This work constructed a series of unique phenylhydrazone-based oxindole-thiolazoles to combat monstrous bacterial resistance. Some target molecules showed potent antibacterial activity, among which oxindole-thiolimidazole derived carboxyphenylhydrazone 4e exhibited an 8-fold stronger inhibitory ability than norfloxacin on the growth of P. aeruginosa, with MIC value of 1 µg/mL. Compound 4e with imperceptible hemolysis could hamper bacterial biofilm formation and significantly impede the development of bacterial resistance. Subsequent mechanism studies demonstrated that 4e could destruct bacterial cytoplasmic membrane, causing the leakage of cellular contents (protein and nucleic acid). Moreover, metabolic stagnation and intracellular oxidative stress caused by 4e expedited the death of bacteria. Furthermore, molecule 4e existed supramolecular interactions with DNA to block DNA proliferation. These research results provided a promising light for phenylhydrazone-based oxindole-thiolazoles as novel potential antibacterial agents.

Novel metronidazole-derived three-component hybrids as promising broad-spectrum agents to combat oppressive bacterial resistance.

The dreadful bacterial resistance to clinical drugs calls for the development of novel antibacterials. This work developed a class of unique metronidazole-derived three-component hybrids as promising antibacterial therapeutic alternatives. Bioactive assay discovered that p-chlorophenylhydrazone derivative 6b possessed excellent ability to suppress the growth of drug-resistant E. coli (MIC = 0.5 µg/mL), being 16 folds more potent than norfloxacin (MIC = 8 µg/mL). The active molecule 6b with imperceptible hemolysis could effectively retard the development of bacterial drug resistance within 30 passages. Moreover, compound 6b displayed a favorable inhibitory effect on E. coli biofilms and could act rapidly in bactericidal efficacy. Subsequent exploration of mechanism revealed that 6b could destruct the bacterial cytoplasmic membrane, leading to the leakage of intracellular protein. The inactivation of lactate dehydrogenase, metabolic stagnation and the accumulation of reactive oxygen species caused by 6b were observed. Furthermore, molecule 6b could form a supramolecular complex with DNA to obstruct DNA replication. These results demonstrated that metronidazole-derived three-component hybrids provided a large potential for deep development as prospective antibacterial agents.

Isatin-derived azoles as new potential antimicrobial agents: Design, synthesis and biological evaluation.

Novel antibiotics are forced to be developed on account of multidrug-resistant bacteria with serious threats to human health. This work developed isatin-derived azoles as new potential antimicrobial agents. Bioactive assay revealed that isatin hybridized 1,2,4-triazole 7a exhibited excellent inhibitory activity against E. coli ATCC 25,922 with an MIC value of 1 µg/mL, which was 8-fold more potent than reference drug norfloxacin. The active molecule 7a possessed the ability to kill some bacteria and fungi as well as displayed low propensity to induce resistance towards E. coli ATCC25922. Preliminary mechanism investigation indicated that hybrid 7a might block deoxyribonucleic acid (DNA) replication by intercalating with DNA and possibly interacting with DNA polymerase III, thus exerting its antimicrobial potency.

Structure-activity relationship studies and bioactivity evaluation of 1,2,3-triazole containing analogues as a selective sphingosine kinase-2 inhibitors.

Sphingosine kinase (SphK) is primarily responsible for the production of Sphingosine-1-phosphate (S1P) that plays an important role in many biological and pathobiological processes including cancer, inflammation, neurological and cardiovascular disorders. Most research has focused on developing inhibitors of SphK1 rather than inhibitors of the other isoform SphK2 which has great importance in several pathophysiologic pathways. Exploration of new analogues for improving the potency and selectivity of SphK2 inhibitors is critical. We now have designed, synthesized, and evaluated eighteen new 1,2,3-triazole analogues for their SphK2 inhibitory activity using a ADP-Glo kinase assay, and explored their in vivo anti-tumor bioactivity. Several compounds including 21c, 21e, 21g, 25e-h, 29a-c have high selectivity for SphK2 over SphK1; compound 21g displayed the highest potency with an IC50 value of 0.23 µM. In addition, three compounds 21a, 21b, and 25b have high anti-tumor activity against U-251 MG human glioblastoma cells. Molecular modeling study was performed to elucidate the polar head group and 1,2,3-triazole pharmacophore impact on the SphK2 selectivity.

Indole-nitroimidazole conjugates as efficient manipulators to decrease the genes expression of methicillin-resistant Staphylococcus aureus.

The biological resistance of methicillin-resistant staphylococcus aureus (MRSA) has pushed synthetic antibiotics to the forefront. To combat the resistance of MRSA, our new effort directed towards the development of novel structural candidates of enone-bridged indole nitroimidazole scaffolds, and wished to shed some light on the combination of some single pharmacophore with different biological activities. Bioassay revealed that the active compound 4b gave a satisfactory inhibition on MRSA (MIC = 1 µg/mL) and could effectively prevent the development of bacterial resistance. Mechanism exploration indicated that molecule 4b could not only intercalate into MRSA deoxyribonucleic acid (DNA), but also permeate MRSA membrane and bind with penicillin-binding protein 2a (PBP2a), then decreased the expression of three relevant genes in MRSA. Furthermore, it was able to be stored and carried by human serum albumin (HSA), and the participation of metal ions in 4b-HSA system was helpful to improve the supramolecular transport behavior. Hybrid 4b also exhibited low cytotoxicity towards normal lung epithelial cell line BEAS-2B.

Novel organophosphorus aminopyrimidines as unique structural DNA-targeting membrane active inhibitors towards drug-resistant methicillin-resistant Staphylococcus aureus.

A series of novel unique structural organophosphorus aminopyrimidines were developed as potential DNA-targeting membrane active inhibitors through an efficient one-pot procedure from aldehydes, phosphonate and aminopyrimidine. The biological assay revealed that some of the prepared compounds displayed antibacterial activities. In particular, imidazole derivative 2c exhibited more potent inhibitory activity against MRSA with an MIC value of 4 µg mL-1 in comparison with the clinical drugs chloromycin and norfloxacin. Experiments revealed that the active molecule 2c had the ability to rapidly kill the tested strains without obviously triggering the development of bacterial resistance, showed low toxicity to L929 cells and could disturb the cell membrane. The molecular docking study discovered that compound 2c could bind with DNA gyrase via hydrogen bonds and other weak interactions. Further exploration disclosed that the active molecule 2c could also effectively intercalate into MRSA DNA and form a steady 2c-DNA supramolecular complex, which might further block DNA replication to exert powerful antibacterial effects.

Azoalkyl ether imidazo[2,1-b]benzothiazoles as potentially antimicrobial agents with novel structural skeleton.

A series of new azoalkyl ether imidazo[2,1-b]benzothiazoles were developed via a convenient synthetic procedure. The antimicrobial assays showed that a good number of the prepared derivatives exhibited significant inhibitory properties against most of the tested strains. Especially 2-methyl-5-nitroimidazole derivative 5a presented superior inhibit activity against MRSA and B. typhi with MIC = 4 µg/mL and MIC = 1 µg/mL, respectively. The highly active compound 5a showed low toxicity against mammalian cells without obvious triggering of the development of bacterial resistance, and it also possessed rapid bactericidal efficacy. Molecular docking study exposed that the active molecule 5a could interact with the active site of S. aureus gyrase through hydrogen bond. Quantum chemical studies were also performed to explain the high antibacterial activity. Further investigation revealed that compound 5a could significantly associate with gyrase-DNA complex by mean of hydrogen bonds and could efficiently intercalate into MRSA DNA to form 5a-DNA supramolecular complex, which impart potent bioactivity.

Novel carbazole-triazole conjugates as DNA-targeting membrane active potentiators against clinical isolated fungi.

A series of carbazole-triazole conjugates were designed, synthesized and characterized by IR, NMR, and HRMS spectra. Biological assay showed that most of the synthesized compounds exhibited moderate and even strong antifungal activities, especially 3,6-dibromocarbazolyl triazole 5d displayed excellent inhibitory efficacy against most of the tested fungal strains (MIC = 2-32 µg/mL) and effectively fungicidal ability towards C. albicans, C. tropicals and C. parapsilosis ATCC 22019 (MFC = 4-8 µg/mL). Its combination use with fluconazole could enhance the antifungal efficacy, and compound 5d also did not obviously trigger the development of resistance in C. albicans even after 10 passages. Preliminary mechanism study revealed that the active molecule 5d could depolarize fungal membrane potential and intercalate into DNA to possibly block DNA replication, thus possibly exhibiting its powerful antifungal abilities. Conjugate 5d could interact with HSA, which was constructive for the further design, modification and screening of drug molecules. Docking investigation demonstrated a non-covalent binding of 5d with CYP51 through hydrogen bond and hydrophobicity. These results strongly suggested that compound 5d could act as a potential template for the development of promising antifungal drugs.

Potential Antimicrobial Isopropanol-Conjugated Carbazole Azoles as Dual Targeting Inhibitors of Enterococcus faecalis.

A series of isopropanol-bridged carbazole azoles as potential antimicrobial agents were designed and synthesized from commercial carbazoles. Bioassay revealed that 3,6-dichlorocarbazolyl triazole 3f could effectively inhibit the growth of E. faecalis with minimal inhibitory concentration of 2 µg/mL. The active molecule 3f showed lower propensity to trigger the development of resistance in bacteria than norfloxacin and exerted rapidly bactericidal ability. Compound 3f also exhibited low cytotoxicity to normal mammalian RAW264.7 cells. Further mechanism exploration indicated that conjugate 3f was membrane active against E. faecalis and could form 3f-DNA complex by intercalating into DNA of resistant E. faecalis, which might be responsible for its antimicrobial action. Molecular docking showed an efficient binding of triazole derivative 3f with DNA gyrase enzyme through noncovalent interactions.

Novel aminopyrimidinyl benzimidazoles as potentially antimicrobial agents: Design, synthesis and biological evaluation.

A series of novel aminopyrimidinyl benzimidazoles as potentially antimicrobial agents were designed, synthesized and characterized by IR, NMR and HRMS spectra. The biological evaluation in vitro revealed that some of the target compounds exerted good antibacterial and antifungal activity in comparison with the reference drugs. Noticeably, compound 7d could effectively inhibit the growth of A. flavus, E. coli DH52 and MRSA with MIC values of 1, 1 and 8 µg/mL, respectively. Further studies revealed that pyrimidine derivative 7d could exhibit bactericidal mode of action against both Gram positive (S. aureus and MRSA) and Gram negative (P. aeruginosa) bacteria. The active molecule 7d showed low cell toxicity and did not obviously trigger the development of resistance in bacteria even after 16 passages. Furthermore, compound 7d was able to beneficially regulate reactive oxygen species (ROS) generation for an excellent safety profile. Molecular docking study revealed that compound 7d could bind with DNA gyrase by the formation of hydrogen bonds. The preliminary exploration for antimicrobial mechanism disclosed that compound 7d could effectively intercalate into calf thymus DNA to form a steady supramolecular complex, which might further block DNA replication to exert the powerful bioactivities. The binding investigation of compound 7d with human serum albumins (HSA) revealed that this molecule could be effectively transported by HSA.

Discovery of novel nitroimidazole enols as Pseudomonas aeruginosa DNA cleavage agents.

A series of nitroimidazole enols as new bacterial DNA-targeting agents were for the first time designed, synthesized and characterized by NMR, IR and HRMS spectra. The antimicrobial screening revealed that 2-methoxyphenyl nitroimidazole enol 3i possessed stronger anti-P. aeruginosa efficacy (MIC = 0.10 µmol/mL) than reference drugs Norfloxacin and Metronidazole. Time-kill kinetic assay manifested that the active molecule 3i could rapidly kill the tested strains. Molecular docking indicated that the interactions between compound 3i and topoisomerase II were driven by hydrogen bonds. Quantum chemical study was also performed on 3i to understand the structural features essential for activity. Further research found that compound 3i was not able to effectively intercalate into bacterial DNA but could cleave DNA isolated from the standard P. aeruginosa strain, which might block DNA replication to exert the efficient bioactivities, and this active molecule was also able to be stored and carried by human serum albumin via hydrophobic interactions and hydrogen bonds.

Novel potentially antifungal hybrids of 5-flucytosine and fluconazole: Design, synthesis and bioactive evaluation.

A series of novel potentially antifungal hybrids of 5-flucytosine and fluconazole were designed, synthesized and characterized by 1H NMR, 13C NMR, IR and HRMS spectra. Bioactive assay manifested that some prepared compounds showed moderate to good antifungal activities in comparison with fluconazole and 5-flucytosine. Remarkably, the 3,4-dichlorobenzyl hybrid 7h could inhibit the growth of C. albicans ATCC 90023 and clinical resistant strain C. albicans with MIC values of 0.008 and 0.02 mM, respectively. The active molecule 7h could not only rapidly kill C. albicans but also efficiently permeate membrane of C. albicans. Molecular docking study revealed that compound 7h could interact with the active site of CACYP51 through hydrogen bond. Quantum chemical studies were also performed to explain the high antifungal activity. Further preliminary mechanism research suggested that molecule 7h could intercalate into calf thymus DNA to form a steady supramolecular complex, which might block DNA replication to exert the powerful bioactivities.

Design, synthesis and antimicrobial evaluation of novel benzimidazole-incorporated sulfonamide analogues.

A novel series of benzimidazole-incorporated sulfonamide analogues were designed and synthesized with an effort to overcome the increasing antibiotic resistance. Compound 5c gave potent activities against Gram-positive bacteria and fungi, and 2,4-dichlorobenzyl derivative 5g showed good activities against Gram-negative bacteria. Both of these two active molecules 5c and 5g could effectively intercalate into calf thymus DNA to form compound-DNA complex respectively, which might block DNA replication to exert their powerful antimicrobial activity. Molecular docking experiments suggested that compounds 5c and 5g could insert into base-pairs of DNA hexamer duplex by the formation of hydrogen bonds with guanine of DNA. The transportation behavior of these highly active compounds by human serum albumin (HSA) demonstrated that the electrostatic interactions played major roles in the strong association of active compounds with HSA, and which was also confirmed by the full geometry calculation optimizations.

Discovery of potential antifungal triazoles: design, synthesis, biological evaluation, and preliminary antifungal mechanism exploration.

A series of triazoles as miconazole analogues was designed, synthesized and characterized by IR, NMR, MS and HRMS. All the newly prepared compounds were screened for their antifungal activities against five kinds of fungi. The bioactive assay showed that most of the synthesized compounds exhibited good or even stronger antifungal activities in comparison with the reference drugs miconazole and fluconazole. In particular, the 3,4-dichlorobenzyl derivative 5b showed a comparable or superior activity against all the tested fungal strains to standard drugs, and formed a supramolecular complex with CYP51 via the hydrogen bond between the 4-nitrogen of the triazole nucleus and the histidine residue. Preliminary experiments revealed that both of the active molecules 5b and 9c could intercalate into calf thymus DNAs, which might block DNA replication to exhibit their powerful antifungal abilities. Further studies indicated that compound 5b might be stored and transported by human serum albumin through hydrophobic interactions, specific electrostatic interactions and hydrogen bonds. These results strongly suggested that compound 5b could serve as a promising antifungal candidate.

Multi-targeting exploration of new 2-aminothiazolyl quinolones: Synthesis, antimicrobial evaluation, interaction with DNA, combination with topoisomerase IV and penetrability into cells.

A series of new potentially multi-targeting antimicrobial 2-aminothiazolyl quinolones were designed, synthesized and characterized by 1H NMR, 13C NMR, IR, MS and HRMS spectra. Bioactive assay manifested that some of the prepared compounds showed moderate to good antibacterial and antifungal activities. Noticeably, compound 10f could effectively inhibit the growth of B. typhi and MRSA with MIC values of 1 and 8 µg/mL, respectively. Experimental results revealed that compound 10f was membrane-active and had the ability to rapidly kill the tested strains and effectively prevent the development of bacterial resistance. Moreover, this compound also exhibited low toxicity against L929 cells. Molecular docking indicated that compound 10f could bind with topoisomerase IV-DNA complexes through hydrogen bonds and hydrophobic interactions. Quantum chemical studies were also performed on 10f to understand the structural features essential for activity. The preliminary mechanism research suggested that compound 10f could intercalate into calf thymus DNA to form a steady supramolecular complex which might block DNA replication to exert the powerful bioactivities.