Syntheses and Biofilm Reducing Effects of l-Dopa-Derived Analogues of the Fungal Macrocidins A and Z.

Four analogues of the fungal metabolites macrocidin A and Z, featuring [13]para- or [13]metacyclophanes, were synthesised from fully and orthogonally protected l-dopa instead of l-tyrosine. They were tested for antibiotic activities and for effects on the growth and persistence of microbial biofilms. Tentative structure-activity relationships and distinct differences when compared with the natural lead compounds were identified.

Versatile anti-infective properties of pyrido- and dihydropyrido[2,3-d]pyrimidine-based compounds.

A series of 1H-indeno[2',1':5,6]dihydropyrido[2,3-d]pyrimidine and 1H-indeno[2',1':5,6]pyrido[2,3-d]pyrimidine derivatives was prepared and screened for antiparasitic and viral RNase H inhibitory activity. Several compounds showed considerable activity against Toxoplasma gondii parasites and Leishmania major amastigotes, which warrants further investigation. Based on the structural similarities of certain derivatives with common viral RNase H inhibitors, a HIV-1 RNase H assay was used to study the RNase H inhibition by selected test compounds. Docking of active derivatives into the active site of the HIV-1 RNase H enzyme was carried out. The new compound 2a, inactive in the antiparasitic tests, showed distinct HIV-1 RNase H inhibition. Thus, ring substitution determines antiparasitic or HIV-1 RNase H inhibitory activity of this promising compound class.

Divergent Synthesis of Six Recent Berkeleylactones.

The six recently isolated berkeleylactones E, J, K, M, N, and O were synthesized for the first time by a divergent strategy starting from a common intermediate in our synthesis of berkeleylactone A. Key features were the stereoselective formation of the γ,δ-dihydroxy-α,ß-unsaturated ester moiety and the development of a general protection group strategy. Along the way we also established a short high-yielding formal synthesis of the often-synthesized antibiotic A26771B.

Syntheses and Antibacterial Evaluation of New Penicillium Metabolites Gregatins G and Thiocarboxylics C.

Two pairs of side-chain epimeric 3-methoxycarbonyl-dihydrofuran-4-ones with structures purported for thiocarboxylics C1/2 and gregatins G1/2 , isolated from Penicillium sp. Sb62, were synthesised for the first time in five steps and 17-25 % yield. Key steps were a Suzuki cross-coupling, a Yamaguchi esterification, and a base-induced Knoevenagel-type condensation. The optimum protecting group for the 10-OH group in the dienyl side-chain, orthogonal to necessary protecting groups on O-10 of the furanone, was found to be t-butyldiphenylsilyl (TBDPS). The specific rotations of our synthetic products deviated markedly from those reported for the natural isolates. In contrast to the isolates, the synthetic products were not active against Escherichia coli and Staphylococcus aureus bacteria.

Targeting Colon Cancer Cells with Pyrazino-Imidazolinone Derivatives: Synthesis, Molecular Docking, and in Vitro Evaluation of Anti-Proliferative and Pro-Apoptotic Activities.

We report the synthesis, spectroscopic characterization, molecular docking and biological evaluation of nine pyrazino-imidazolinone derivatives. These derivatives were evaluated for their anticancer activity against three cancer cell lines: 518A2 melanoma, HCT-116, and HCT-116 p53 knockout mutant colon carcinoma. The MTT assay was employed to assess their effectiveness. Among the nine compounds tested, four compounds (5 a, 5 d, 5 g, and 5 h) exhibited promising antiproliferative activity specifically against HCT-116 p53-negative cells (IC50 0.23, 0.20, 2.07 and 58.75 µM, respectively). Interestingly, treatment with the 3,4-dimethoxyphenyl derivative 5a resulted in a significant increase (199 %) in caspase activity in HCT-116 p53-negative cells compared to untreated cells while the bromo-pyrazine derivative 5d demonstrated (190 %) increase. These findings suggest that compounds 5a and 5 d induce p53-independent apoptotic cell death. Additionally, in silico molecular docking studies with EGFR and tyrosinase proteins indicated that compounds 5 d and 5 e have the potential to bind to important anticancer drug targets.

Regiospecific Reduction of 4,6-Dinitrobenzimidazoles: Synthesis, Characterization, and Biological Evaluation.

The regiospecific reduction of 4,6-dinitrobenzimidazole derivatives leading to the corresponding 4-amino-6-nitrobenzimidazoles was studied. The identification of the formed product structures was accomplished by spectroscopic and X-ray diffraction data. The anticancer and antiparasitic activities of the synthesized compounds were examined, and promising activities against Toxoplasma gondii and Leishmania major parasites were discovered for certain 4,6-dinitrobenzimidazoles in addition to moderate anticancer activities of the 4-amino-6-nitrobenzimidazole derivatives against T. gondii cells. However, the tumor cell experiments revealed a promising sensitivity of p53-negative colon cancer cells to these compounds.

New chimeric HDAC inhibitors for the treatment of colorectal cancer.

Colorectal cancer is the third most common cause of cancer-associated deaths due to a high recurrence rate and an increasing occurrence of resistance to established therapies. This highlights the importance of developing new chemotherapeutic agents. The current study focuses on cancer-specific targets such as apoptosis-inhibiting survivin, which distinguishes cancer cells from healthy tissue. A combination of pharmacophores of established anticancer agents to afford chimeric pleiotropic chemotherapeutic agents was tested on this cancer entity. We analysed the effects of the dual mode anticancer agents, animthioxam, brimbam, troxbam, and troxham, as well as their structural congeners suberoylanilide hydroxamic acid and combretastatin A-4 on human cancer cell lines. Their cytotoxicity was determined using the MTT assay, further techniques for detecting apoptotic events, cell cycle analyses, clonogenic and wound healing assays, immunostaining, histone deacetylase (HDAC) activity measurements, and Western blot analysis for the detection of survivin expression in HCT116 colon cancer cells. Molecular docking studies were conducted to assess potential molecular targets of the test compounds. The test compounds were found selectively cytotoxic toward cancer cells by inducing apoptosis. The metastatic potential was effectively reduced by disruption of the microtubular cytoskeleton. The test compounds were also proven to be general HDAC inhibitors and to lead to reduced survivin expression.

Synthesis and Anticancer Evaluation of New Indole-Based Tyrphostin Derivatives and Their (p-Cymene)dichloridoruthenium(II) Complexes.

New N-alkylindole-substituted 2-(pyrid-3-yl)-acrylonitriles with putative kinase inhibitory activity and their (p-cymene)Ru(II) piano-stool complexes were prepared and tested for their antiproliferative efficacy in various cancer models. Some of the indole-based derivatives inhibited tumor cell proliferation at (sub-)micromolar concentrations with IC50 values below those of the clinically relevant multikinase inhibitors gefitinib and sorafenib, which served as positive controls. A focus was set on the investigation of drug mechanisms in HCT-116 p53-knockout colon cancer cells in order to evaluate the dependence of the test compounds on p53. Colony formation assays as well as experiments with tumor spheroids confirmed the excellent antineoplastic efficacy of the new derivatives. Their mode of action included an induction of apoptotic caspase-3/7 activity and ROS formation, as well as anti-angiogenic properties. Docking calculations with EGFR and VEGFR-2 identified the two 3-aryl-2-(pyrid-3-yl)acrylonitrile derivatives 2a and 2b as potential kinase inhibitors with a preferential activity against the VEGFR-2 tyrosine kinase. Forthcoming studies will further unveil the underlying mode of action of the promising new derivatives as well as their suitability as an urgently needed novel approach in cancer treatment.

New 4,5-Diarylimidazol-2-ylidene-iodidogold(I) Complexes with High Activity against Esophageal Adenocarcinoma Cells.

Inspired by the vascular-disrupting agent combretastatin A-4 and recently published anticancer active N-heterocyclic carbene (NHC) complexes of Au(I), a series of new iodidogold(I)-NHC complexes was synthesized and characterized. The iodidogold(I) complexes were synthesized by a route involving van Leusen imidazole formation and N-alkylation, followed by complexation with Ag2O, transmetalation with chloro(dimethylsulfide)gold(I) [Au(DMS)Cl], and anion exchange with KI. The target complexes were characterized by IR spectroscopy, 1H and 13C NMR spectroscopy, and mass spectrometry. The structure of 6c was validated via single-crystal X-ray diffraction. A preliminary anticancer screening of the complexes using two esophageal adenocarcinoma cell lines showed promising nanomolar activities for certain iodidogold(I) complexes accompanied with apoptosis induction, as well as c-Myc and cyclin D1 suppression in esophageal adenocarcinoma cells treated with the most promising derivative 6b.

Palladium and Platinum Complexes of the Antimetabolite Fludarabine with Vastly Enhanced Selectivity for Tumour over Non-Malignant Cells.

The purine derivative fludarabine is part of frontline therapy for chronic lymphocytic leukaemia (CLL). It has shown positive effects on solid tumours such as melanoma, breast, and colon carcinoma in clinical phase I studies. As the treatment of CLL cells with combinations of fludarabine and metal complexes of antitumoural natural products, e.g., illudin M ferrocene, has led to synergistically enhanced apoptosis, in this research study different complexes of fludarabine itself. Four complexes bearing a trans-[Br(PPh3)2]Pt/Pd fragment attached to atom C-8 via formal η1-sigma or η2-carbene bonds were synthesised in two or three steps without protecting polar groups on the arabinose or adenine. The platinum complexes were more cytotoxic than their palladium analogues, with low single-digit micromolar IC50 values against cells of various solid tumour entities, including cisplatin-resistant ones and certain B-cell lymphoma and CLL, presumably due to the ten-fold higher cellular uptake of the platinum complexes. However, the palladium complexes interacted more readily with isolated Calf thymus DNA. Interestingly, the platinum complexes showed vastly greater selectivity for cancer over non-malignant cells when compared with fludarabine.

Chemical properties of key metabolites determine the global distribution of lichens.

In lichen symbioses, fungal secondary metabolites provide UV protection on which lichen algae such as trebouxiophycean green algae-the most prominent group of photobionts in lichen symbioses-sensitively depend. These metabolites differ in their UV absorbance capability and solvability, and thus vary in their propensity of being leached from the lichen body in humid and warm environments, with still unknown implications for the global distribution of lichens. In this study covering more than 10,000 lichenised fungal species, we show that the occurrence of fungal-derived metabolites in combination with their UV absorbance capability and their probability of being leached in warm and humid environments are important eco-evolutionary drivers of global lichen distribution. Fungal-derived UV protection seems to represent an indirect environmental adaptation in which the lichen fungus invests to protect the trebouxiophycean photobiont from high UV radiation in warm and humid climates and, by doing this, secures its carbon source.

3D cell cultures, as a surrogate for animal models, enhance the diagnostic value of preclinical in vitro investigations by adding information on the tumour microenvironment: a comparative study of new dual-mode HDAC inhibitors.

Anchorage-independent 3D-cultures of multicellular tumour spheroids (MCTS) and in vitro microtumours of cancer cells can provide upfront information on the effects of anticancer drug candidates, tantamount to that obtained from animal xenograft studies. Unlike 2D cancer cell cultures, 3D-models take into account the influence of the tumour microenvironment and the location dependence of drug effects and accumulation. We exemplified this by comparison of the effects of two new dual-mode anticancer agents, Troxbam and Troxham, and their monomodal congeners SAHA (suberoylanilide hydroxamic acid) and CA-4 (combretastatin A-4). We assessed the growth of MCTS of HCT116wt human colon carcinoma cells exposed to these compounds, as well as the spatial distribution of dead HCT116wt cells in these MCTS. Also, fluorescence imaging of live and fixed MCTS was used to assess the type of cellular death induced by test compounds. Furthermore, an innovative perfusion bioreactor system was used to grow microtumours in the presence or absence of test compounds. Both new investigational compounds led to significant reductions of the size of such MCTS and also of corresponding in vitro microtumours by inducing caspase-9 dependent apoptosis and elevated levels of reactive oxygen species. 3D multicellular tumour spheroids are easy to grow and employ for compound tests in the familiar well-plate set-up. Together with 3D microtumours grown at scaffolds in continuously perfused bioreactors they allow to study, early on in the course of drug evaluations, the communication of tumour cells with their microenvironment to an extent hitherto available only in animal experiments.

Revisiting the anticancer properties of phosphane(9-ribosylpurine-6-thiolato)gold(I) complexes and their 9H-purine precursors.

New mono- and di-nuclear thio-purine and thio-purine nucleoside gold(I) complexes were synthesized, characterized, and evaluated in vitro for biological activities in comparison to related known purine complexes. By combining known anti-tumoral thio-purines with R3PAu moieties as present in auranofin, complexes with enhanced effects and selectivities were obtained, which not only act as cytostatics, but also disrupt tumor-specific processes. Their IC50 values in cytotoxicity test with tumor cell lines ranged from three-digit nanomolar to single-digit micromolar, revealing a tentative structure-activity relationship (SAR). Both the residues R2 of the phosphane ligand and R1 at C2 of the pyrimidine ring had a significant impact on the cytotoxicity. In most cases, the introduction of a ribo-furanosyl group at N9 of the purine led to a distinctly more cytotoxic complex. Most complexes were more active against multi-drug-resistant tumor cells or such lacking functional p53 when compared to the respective untreated wild type cell lines. Some nucleoside complexes displayed an interesting dose-dependent dual mode of action regarding cell cycle arrest and DNA repair mechanism. Some phosphane(purine-6-thiolato)gold (I) complexes had a stronger inhibitory effect on the thioredoxin reductase (TrxR) and on the reactive oxygen species (ROS) generation in cancer cells than is typical of other gold complexes. They also led to DNA fragmentation and showed anti-angiogenic effects. Their stability under test conditions was demonstrated by 77Se NMR monitoring of an exemplary selenopurine complex.

Synthesis and Bioactivity of Ophiofuranones A and B.

Ophiofuranones A and B, metabolites of the fungus Ophiosphaerella korrae, were synthesized in 16 steps and 12%/22% yield. The stereogenic centers were established by Sharpless dihydroxylations and epoxidation, the 1,3-dienes via Wittig or HWE olefinations. The rings were closed through Knoevenagel-type condensation and lactonization. The ophiofuranones proved nontoxic at relevant concentrations against tumor cells, fibroblasts, and various bacteria and fungi. Ophiofuranone A and the monocyclic precursors 4 were weakly active against microbial biofilms.

Syntheses and biological effects of natural Morinda lactone and derivatives.

2-Caffeoyl-3-ketohexulofuranosonic acid γ-lactone (morinda lactone; 1a), a natural constituent of Morinda citrifolia L. (Rubiaceae), and eight derivatives with variance in the aryl residue were synthesised by Tsuji-Trost allylation of vitamin C acetonide with the respective aryl allyl alcohol. They were screened for antibiotic activities and for effects on the growth and persistence of microbial biofilms. Some derivatives were active against biofilms of S. aureus or C. albicans at concentrations not toxic to these microorganisms or mammalian cells.

Synthesis and Bioactivity of Thiocarboxylic A and Derivatives.

The Penicillium metabolite thiocarboxylic A (1a) and three close analogues were synthesized in 14 steps. The stereogenic elements were installed via stereoselective Sharpless epoxidation, (E)-selective reduction of a dibromide, and a Suzuki cross coupling. Thiocarboxylic A (1a) was obtained in 6% overall yield. The synthetic product and the natural isolate differed markedly in their specific rotations and antibiotic activities against Escherichia coli and Staphylococcus aureus. This modular synthetic route should be flexible enough to allow the synthesis of other natural and non-natural 3-methoxycarbonyldihydrofuran-4-ones for biological studies.

An Update on Natural Antileishmanial Treatment Options from Plants, Fungi and Algae.

Efficient drugs for the treatment of leishmaniasis, which is classified as a neglected tropical disease, are sought for. This review covers potential drug candidates from natural plant, fungus and algae sources, which were described over the last six years. The identification of these natural antileishmanials often based on the knowledge of traditional medicines. Crucial insights into the activities of these natural remedies against Leishmania parasites and against infections caused by these parasites in laboratory animals or patients are provided and compared with selected former active examples published more than six years ago. In addition, immuno-modulatory natural antileishmanials and recent developments on combination therapies including natural products and approved antileishmanials are discussed. The described natural products revealed promising data warranting further efforts on the discovery and development of new antileishmanials based on patterns from nature.

Antitumor Effects of a New Retinoate of the Fungal Cytotoxin Illudin M in Brain Tumor Models.

While the fungal metabolite illudin M (1) is indiscriminately cytotoxic in cancer and non-malignant cells, its retinoate 2 showed a greater selectivity for the former, especially in a cerebral context. Illudin M killed malignant glioma cells as well as primary neurons and astrocytes at similarly low concentrations and destroyed their microtubule and glial fibrillary acidic protein (GFAP) networks. In contrast, the ester 2 was distinctly more cytotoxic in highly dedifferentiated U87 glioma cells than in neurons, which were even stimulated to enhanced growth. This was also observed in co-cultures of neurons with U87 cells where conjugate 2 eventually killed them by induction of differentiation based on the activation of nuclear receptors, which bind to retinoid-responsive elements (RARE). Hence, illudin M retinoate 2 appears to be a promising drug candidate.

Guided Antitumoural Drugs: (Imidazol-2-ylidene)(L)gold(I) Complexes Seeking Cellular Targets Controlled by the Nature of Ligand L.

Three [1,3-diethyl-4-(p-methoxyphenyl)-5-(3,4,5-trimethoxyphenyl)imidazol-2-ylidene](L)gold(I) complexes, 4 a (L=Cl), 5 a (L=PPh3 ), and 6 a (L=same N-heterocyclic carbene (NHC)), and their fluorescent [4-(anthracen-9-yl)-1,3-diethyl-5-phenylimidazol-2-ylidene](L)gold(I) analogues, 4 b, 5 b, and 6 b, respectively, were studied for their localisation and effects in cancer cells. Despite their identical NHC ligands, the last three accumulated in different compartments of melanoma cells, namely, the nucleus (4 b), mitochondria (5 b), or lysosomes (6 b). Ligand L was also more decisive for the site of accumulation than the NHC ligand because the couples 4 a/4 b, 5 a/5 b, and 6 a/6 b, carrying different NHC ligands, afforded similar results in cytotoxicity tests, and tests on targets typically found at their sites of accumulation, such as DNA in nuclei, reactive oxygen species and thioredoxin reductase in mitochondria, and lysosomal membranes. Regardless of the site of accumulation, cancer cell apoptosis was eventually induced. The concept of guiding a bioactive complex fragment to a particular subcellular target by secondary ligand L could reduce unwanted side effects.

Synthesis of the Proposed Isomers of the Deep-Sea Mussel Metabolites Bathymodiolamides A and B.

The first total synthesis of bathymodiolamides A and B, ceramide-like metabolites of the deep-sea hydrothermal vent mussel Bathymodiolus thermophilus, was accomplished in eight linear steps starting from Garner's aldehyde and three carboxylic acids. A sequence of vinylation of Garner's aldehyde, N-acylation with lauric acid, dihydroxylation of the terminal alkene, and stepwise Steglich-Hassner esterifications of the resulting vicinal diol with the respective saturated and unsaturated carboxylic acids, which had to be prepared separately, afforded the target products in 38 and 39% yield. We found distinct discrepancies between their NMR data and antiproliferative activities and those reported for the natural isolates.