Harvesting phosphorus-containing moieties for their antibacterial effects.

Clinically manifested resistance of bacteria to antibiotics has emerged as a global threat to society and there is an urgent need for the development of novel classes of antibacterial agents. Recently, the use of phosphorus in antibacterial agents has been explored in quite an unprecedent manner. In this comprehensive review, we summarize the use of phosphorus-containing moieties (phosphonates, phosphonamidates, phosphonopeptides, phosphates, phosphoramidates, phosphinates, phosphine oxides, and phosphoniums) in compounds with antibacterial effect, including their use as ß-lactamase inhibitors and antibacterial disinfectants. We show that phosphorus-containing moieties can serve as novel pharmacophores, bioisosteres, and prodrugs to modify pharmacodynamic and pharmacokinetic properties. We further discuss the mechanisms of action, biological activities, clinical use and highlight possible future prospects.

Structure-Function Studies of Sponge-Derived Compounds on the Cardiac CaV3.1 Channel.

T-type calcium (CaV3) channels are involved in cardiac automaticity, development, and excitation-contraction coupling in normal cardiac myocytes. Their functional role becomes more pronounced in the process of pathological cardiac hypertrophy and heart failure. Currently, no CaV3 channel inhibitors are used in clinical settings. To identify novel T-type calcium channel ligands, purpurealidin analogs were electrophysiologically investigated. These compounds are alkaloids produced as secondary metabolites by marine sponges, and they exhibit a broad range of biological activities. In this study, we identified the inhibitory effect of purpurealidin I (1) on the rat CaV3.1 channel and conducted structure-activity relationship studies by characterizing the interaction of 119 purpurealidin analogs. Next, the mechanism of action of the four most potent analogs was investigated. Analogs 74, 76, 79, and 99 showed a potent inhibition on the CaV3.1 channel with IC50's at approximately 3 µM. No shift of the activation curve could be observed, suggesting that these compounds act like a pore blocker obstructing the ion flow by binding in the pore region of the CaV3.1 channel. A selectivity screening showed that these analogs are also active on hERG channels. Collectively, a new class of CaV3 channel inhibitors has been discovered and the structure-function studies provide new insights into the synthetic design of drugs and the mechanism of interaction with T-type CaV channels.

Imitation of ß-lactam binding enables broad-spectrum metallo-ß-lactamase inhibitors.

Carbapenems are vital antibiotics, but their efficacy is increasingly compromised by metallo-ß-lactamases (MBLs). Here we report the discovery and optimization of potent broad-spectrum MBL inhibitors. A high-throughput screen for NDM-1 inhibitors identified indole-2-carboxylates (InCs) as potential ß-lactamase stable ß-lactam mimics. Subsequent structure-activity relationship studies revealed InCs as a new class of potent MBL inhibitor, active against all MBL classes of major clinical relevance. Crystallographic studies revealed a binding mode of the InCs to MBLs that, in some regards, mimics that predicted for intact carbapenems, including with respect to maintenance of the Zn(II)-bound hydroxyl, and in other regards mimics binding observed in MBL-carbapenem product complexes. InCs restore carbapenem activity against multiple drug-resistant Gram-negative bacteria and have a low frequency of resistance. InCs also have a good in vivo safety profile, and when combined with meropenem show a strong in vivo efficacy in peritonitis and thigh mouse infection models.

Synthesis and Cytotoxicity Evaluation of Spirocyclic Bromotyrosine Clavatadine C Analogs.

Marine-originated spirocyclic bromotyrosines are considered as promising scaffolds for new anticancer drugs. In a continuation of our research to develop potent and more selective anticancer compounds, we synthesized a library of 32 spirocyclic clavatadine analogs by replacing the agmatine, i.e., 4-(aminobutyl)guanidine, side chain with different substituents. These compounds were tested for cytotoxicity against skin cancer using the human melanoma cell line (A-375) and normal human skin fibroblast cell line (Hs27). The highest cytotoxicity against the A-375 cell line was observed for dichloro compound 18 (CC50 0.4 ± 0.3 µM, selectivity index (SI) 2). The variation of selectivity ranged from SI 0.4 to reach 2.4 for the pyridin-2-yl derivative 29 and hydrazide analog of 2-picoline 37. The structure-activity relationships of the compounds in respect to cytotoxicity and selectivity toward cancer cell lines are discussed.

Ketamine-induced regulation of TrkB-GSK3ß signaling is accompanied by slow EEG oscillations and sedation but is independent of hydroxynorketamine metabolites.

Subanesthetic rather than anesthetic doses are thought to bring the rapid antidepressant effects of the NMDAR (N-methyl-d-aspartate receptor) antagonist ketamine. Among molecular mechanisms, activation of BDNF receptor TrkB along with the inhibition of GSK3ß (glycogen synthase kinase 3ß) are considered as critical molecular level determinants for ketamine's antidepressant effects. Hydroxynorketamines (2R,6R)-HNK and (2S,6S)-HNK), non-anesthetic metabolites of ketamine, have been proposed to govern the therapeutic effects of ketamine through a mechanism not involving NMDARs. However, we have shown that nitrous oxide, another NMDAR blocking anesthetic and a putative rapid-acting antidepressant, evokes TrkB-GSK3ß signaling alterations during rebound slow EEG (electroencephalogram) oscillations. We investigated here the acute effects of ketamine, 6,6-d2-ketamine (a ketamine analogue resistant to metabolism) and cis-HNK that contains (2R,6R) and (2S,6S) enantiomers in 1:1 ratio, on TrkB-GSK3ß signaling and concomitant electroencephalographic (EEG) alterations in the adult mouse cortex. Ketamine dose-dependently increased slow oscillations and phosphorylations of TrkBY816 and GSK3ßS9 in crude brain homogenates (i.e. sedative/anesthetic doses (>50 mg/kg, i.p.) produced more prominent effects than a subanesthetic dose (10 mg/kg, i.p.)). Similar, albeit less obvious, effects were seen in crude synaptosomes. A sedative dose of 6,6-d2-ketamine (100 mg/kg, i.p.) recapitulated the effects of ketamine on TrkB and GSK3ß phosphorylation while cis-HNK at a dose of 20 mg/kg produced negligible acute effects on TrkB-GSK3ß signaling or slow oscillations. These findings suggest that the acute effects of ketamine on TrkB-GSK3ß signaling are by no means restricted to subanesthetic (i.e. antidepressant) doses and that cis-HNK is not responsible for these effects.

Asymmetry in catalysis by Thermotoga maritima membrane-bound pyrophosphatase demonstrated by a nonphosphorus allosteric inhibitor.

Membrane-bound pyrophosphatases are homodimeric integral membrane proteins that hydrolyze pyrophosphate into orthophosphates, coupled to the active transport of protons or sodium ions across membranes. They are important in the life cycle of bacteria, archaea, plants, and parasitic protists, but no homologous proteins exist in vertebrates, making them a promising drug target. Here, we report the first nonphosphorus allosteric inhibitor of the thermophilic bacterium Thermotoga maritima membrane-bound pyrophosphatase and its bound structure together with the substrate analog imidodiphosphate. The unit cell contains two protein homodimers, each binding a single inhibitor dimer near the exit channel, creating a hydrophobic clamp that inhibits the movement of ß-strand 1-2 during pumping, and thus prevents the hydrophobic gate from opening. This asymmetry of inhibitor binding with respect to each homodimer provides the first clear structural demonstration of asymmetry in the catalytic cycle of membrane-bound pyrophosphatases.

Synthesis and Antiproliferative Activity of Marine Bromotyrosine Purpurealidin I and Its Derivatives.

The first total synthesis of the marine bromotyrosine purpurealidin I (1) using trifluoroacetoxy protection group and its dimethylated analog (29) is reported along with 16 simplified bromotyrosine derivatives lacking the tyramine moiety. Their cytotoxicity was evaluated against the human malignant melanoma cell line (A-375) and normal skin fibroblast cells (Hs27) together with 33 purpurealidin-inspired simplified amides, and the structure⁻activity relationships were investigated. The synthesized simplified analogs without the tyramine part retained the cytotoxic activity. Purpurealidin I (1) showed no selectivity but its simplified pyridin-2-yl derivative (36) had the best improvement in selectivity (Selectivity index 4.1). This shows that the marine bromotyrosines are promising scaffolds for developing cytotoxic agents and the full understanding of the elements of their SAR and improving the selectivity requires further optimization of simplified bromotyrosine derivatives.

Synthesis of novel purpurealidin analogs and evaluation of their effect on the cancer-relevant potassium channel KV10.1.

In the search for novel anticancer drugs, the potassium channel KV10.1 has emerged as an interesting cancer target. Here, we report a new group of KV10.1 inhibitors, namely the purpurealidin analogs. These alkaloids are produced by the Verongida sponges and are known for their wide variety of bioactivities. In this study, we describe the synthesis and characterization of 27 purpurealidin analogs. Structurally, bromine substituents at the central phenyl ring and a methoxy group at the distal phenyl ring seem to enhance the activity on KV10.1. The mechanism of action of the most potent analog 5 was investigated. A shift of the activation curve to more negative potentials and an apparent inactivation was observed. Since KV10.1 inhibitors can be interesting anticancer drug lead compounds, the effect of 5 was evaluated on cancerous and non-cancerous cell lines. Compound 5 showed to be cytotoxic and appeared to induce apoptosis in all the evaluated cell lines.

Synthesis and Biological Evaluation of 2-Aminobenzothiazole and Benzimidazole Analogs Based on the Clathrodin Structure.

A series of 2-aminobenzothiazole and benzimidazole analogs based on the clathrodin scaffold was synthesized and investigated for their antimicrobial and antiproliferative activities as well as for their effects in hepatitis C virus (HCV) replicon model. Compound 7, derived from 2-aminobenzothiazole, exhibited moderate antimicrobial activity only against the Gram-positive bacterium, Enterococcus faecalis. In the antiviral assay, compounds 4d and 7 were found to suppress the HCV replicon by >70%, but also to exhibit cytotoxicity against the host cells (35 and 44%, respectively). Compounds 4a and 7 demonstrated good activity in the antiproliferative assays on the human melanoma cell line A-375. To assess the selectivity of the effects between cancerous and noncancerous cells, a mouse fibroblast cell line was used. The IC50 values for compound 7 against the melanoma cell line A-375 and the fibroblast cell line BALB/c 3T3 were 16 and 71 µM, respectively, yielding fourfold selectivity toward the cancer cell line. These results suggest that compound 7 should be studied further in order to fully explore its potential for drug development.

A Developability-Focused Optimization Approach Allows Identification of in Vivo Fast-Acting Antimalarials: N-[3-[(Benzimidazol-2-yl)amino]propyl]amides.

Malaria continues to be a major global health problem, being particularly devastating in the African population under the age of five. Artemisinin-based combination therapies (ACTs) are the first-line treatment recommended by the WHO to treat Plasmodium falciparum malaria, but clinical resistance against them has already been reported. As a consequence, novel chemotypes are urgently needed. Herein we report a novel, in vivo active, fast-acting antimalarial chemotype based on a benzimidazole core. This discovery is the result of a medicinal chemistry plan focused on improving the developability profile of an antichlamydial chemical class previously reported by our group.

Synthesis and biological evaluation of 2-arylbenzimidazoles targeting Leishmania donovani.

A set of 56 2-arylbenzimidazoles was designed, synthesized and tested against Leishmania donovani amastigotes. The left- and right-hand side rings of the molecule, as well as the amide linker were modified. Structurally different derivatives were screened on L. donovani axenic amastigotes at concentrations of 5, 15 and 50 µM, and the ten most active derivatives were selected for further testing. 2-Arylbenzimidazole derivative 24 was active against L. donovani-infected THP-1 cells showing 46% parasite inhibition at 5 µM.

Exploring marine resources for bioactive compounds.

Biodiversity in the seas is only partly explored, although marine organisms are excellent sources for many industrial products. Through close co-operation between industrial and academic partners, it is possible to successfully collect, isolate and classify marine organisms, such as bacteria, fungi, micro- and macroalgae, cyanobacteria, and marine invertebrates from the oceans and seas globally. Extracts and purified compounds of these organisms can be studied for several therapeutically and industrially significant biological activities, including anticancer, anti-inflammatory, antiviral, antibacterial, and anticoagulant activities by applying a wide variety of screening tools, as well as for ion channel/receptor modulation and plant growth regulation. Chromatographic isolation of bioactive compounds will be followed by structural determination. Sustainable cultivation methods for promising organisms and biotechnological processes for selected compounds can be developed, as well as biosensors for monitoring the target compounds. The (semi)synthetic modification of marine-based bioactive compounds produces their new derivatives, structural analogs and mimetics that could serve as hit or lead compounds and be used to expand compound libraries based on marine natural products. The research innovations can be targeted for industrial product development in order to improve the growth and productivity of marine biotechnology. Marine research aims at a better understanding of environmentally conscious sourcing of marine biotechnology products and increased public awareness of marine biodiversity. Marine research is expected to offer novel marine-based lead compounds for industries and strengthen their product portfolios related to pharmaceutical, nutraceutical, cosmetic, agrochemical, food processing, material and biosensor applications.

Conformation study of 2-arylbenzimidazoles as inhibitors of Chlamydia pneumoniae growth.

Chlamydia pneumoniae is a worldwide cause of various respiratory track diseases ranging from asymptomatic pharyngeal infection to severe, sometimes fatal pneumonia. We have previously identified 2-arylbenzimidazoles as highly active antichlamydial compounds. In this work the importance of conformational effects on the structure-activity relationship of these compounds was studied. To simplify calculations, properly substituted N-phenylbenzamides, or the corresponding heterocyclic compounds, and 2-arylbenzimidazoles were used as model compounds. They were energy minimized and the energy differences between certain conformations were calculated. The main finding was that the compounds which can more easily adopt a non-planar conformation show higher bioactivity. This finding can be utilized in designing new derivatives or in constructing a pharmacophore model.

Synthesis and evaluation of indatraline-based inhibitors for trypanothione reductase.

The search for novel compounds of relevance to the treatment of diseases caused by trypanosomatid protozoan parasites continues. Screening of a large library of known bioactive compounds has led to several drug-like starting points for further optimisation. In this study, novel analogues of the monoamine uptake inhibitor indatraline were prepared and assessed both as inhibitors of trypanothione reductase (TryR) and against the parasite Trypanosoma brucei. Although it proved difficult to significantly increase the potency of the original compound as an inhibitor of TryR, some insight into the preferred substituent on the amine group and in the two aromatic rings of the parent indatraline was deduced. In addition, detailed mode of action studies indicated that two of the inhibitors exhibit a mixed mode of inhibition.

Design and synthesis of 2-arylbenzimidazoles and evaluation of their inhibitory effect against Chlamydia pneumoniae.

Chlamydia pneumoniae is an intracellular bacterium that responds poorly to antibiotic treatment. Insufficient antibiotic usage leads to chronic infection, which is linked to disease processes of asthma, atherosclerosis, and Alzheimer's disease. The Chlamydia research lacks genetic tools exploited by other antimicrobial research, and thus other approaches to drug discovery must be applied. A set of 2-arylbenzimidazoles was designed based on our earlier findings, and 33 derivatives were synthesized. Derivatives were assayed against C. pneumoniae strain CWL-029 in an acute infection model using TR-FIA method at a concentration of 10 µM, and the effects of the derivatives on the host cell viability were evaluated at the same concentration. Fourteen compounds showed at least 80% inhibition, with only minor changes in host cell viability. Nine most potential compounds were evaluated using immunofluorescence microscopy on two different strains of C. pneumoniae CWL-029 and CV-6. The N-[3-(1H-benzimidazol-2-yl)phenyl]-3-methylbenzamide (42) had minimal inhibitory concentration (MIC) of 10 µM against CWL-029 and 6.3 µM against the clinical strain CV-6. This study shows the high antichlamydial potential of 2-arylbenzimidazoles, which also seem to have good characteristics for lead compounds.

The synthesis of highly functionalised pyridines using Ghosez-type reactions of dihydropyrazoles.

The aza-Diels-Alder reaction of αß-unsaturated hydrazones is a general methodology that has been applied both to the synthesis of natural products and in the development of multicomponent reactions. Trends have emerged as to the effect of substituents on the efficiency of this reaction with substituents at the C2 and C4-positions of the aza-diene in general suppressing the reaction. Here we report that 4,5-dihydropyrazoles can function as substrates in this process despite the presence of substituents at both of these positions. A one pot, four chemical step sequence carried out under standard thermal or microwave conditions results in the formation of the corresponding pyridine-containing compounds. The scope of the reaction is explored and additional insights into the proposed mechanism of this reaction are provided.

Microwave-assisted synthesis of deuterium labeled estrogen fatty acid esters.

Deuterated analogs of estrogen fatty acid esters are needed as internal standards for isotope dilution GC/MS analyses. We have developed a rapid and efficient synthesis for 2,4,16,16-D4-estrone palmitate, stearate, oleate, linoleate, and linolenate and the corresponding 2,4,16,16,17alpha-D5-estradiol fatty acid 17-mono and 3,17-diesters using analogous fatty acid chlorides or fatty acid anhydrides and 4-(dimethylamino)pyridine under microwave irradiation. Chemoselective hydrolysis of fatty acid diesters was carried out by KOH in t-BuOH.

An isotope dilution gas chromatographic-mass spectrometric method for the simultaneous assay of estrogens and phytoestrogens in urine.

The metabolism of endogenous estrogens is complicated and certain metabolic patterns may reflect an individual risk of estrogen-dependent diseases such as breast cancer. Since the 1960s we have been constantly involved in developing estrogen profiling methods, in the beginning using gas chromatography and later gas chromatography-mass spectrometry (GC-MS) in the selected ion monitoring mode (SIM) and finally utilizing isotope dilution (ID-GC-MS-SIM). The addition of the dietary phytoestrogens to the profile rendered the method even more complicated. The present work presents the final estrogen profile method for 15 endogenous estrogens, four lignans, seven isoflavonoids and coumestrol in one small urine sample (1/150th of a 24 h human urine sample, minimum 2.5-5 ml) with complete validation including investigations as to the precision, sensitivity, accuracy and specificity. The method does not include the minimal amounts of unconjugated estrogens in urine. It may also be used for animal (e.g. rat and mouse) urine using a minimum of 2 ml of usually pooled sample. Despite its complexity it was found to fulfill the reliability criteria, resulting in highly specific and accurate results.

Short synthesis of 2-methoxyestradiol and 2-hydroxyestradiol.

The estrogen metabolite 2-methoxyestradiol was synthesized from estradiol bis-THP-ether which was 2-hydroxylated using the superbase LIDAKOR, trimethyl borate, and H(2)O(2), then methylated and deprotected to obtain 2-methoxyestradiol in three steps and 61% yield. 2-Hydroxyestradiol was obtained by deprotecting the 2-hydroxyestradiol bis-THP-ether from the first step.