Bioactivity and Mode of Action of Bacterial Tetramic Acids.

Microbially produced 3-acyltetramic acids display a diverse range of biological activities. The pyreudiones are new members of this class that were isolated from bacteria of the genus Pseudomonas. Here, we performed a structure-activity relationship study and determined their mode of action. An efficient biomimetic synthesis was developed to synthesize pyreudione A. Pyreudiones and synthetic analogs thereof were tested for their amoebicidal, antibacterial, antiproliferative, and cytotoxic activities. The length of the alkyl side chain and the nature of the amino acid residues within the tetramic acid moiety strongly affected activity, in particular against mycobacteria. The mode of action was shown to correlate with the ability of pyreudiones to act as protonophores. Removal of the acidic proton by methylation of pyreudione A resulted in a loss of bioactivity.

Formation of Nudicaulins In Vivo and In Vitro and the Biomimetic Synthesis and Bioactivity of O-Methylated Nudicaulin Derivatives.

Nudicaulins are yellow flower pigments accounting for the color of the petals of Papaver nudicaule (Papaveraceae). These glucosidic compounds belong to the small group of indole/flavonoid hybrid alkaloids. Here we describe in vivo and in vitro experiments which substantiate the strongly pH-dependent conversion of pelargonidin glucosides to nudicaulins as the final biosynthetic step of these alkaloids. Furthermore, we report the first synthesis of nudicaulin aglycon derivatives, starting with quercetin and ending up at the biomimetic fusion of a permethylated anthocyanidin with indole. A small library of nudicaulin derivatives with differently substituted indole units was prepared, and the antimicrobial, antiproliferative and cell toxicity data of the new compounds were determined. The synthetic procedure is considered suitable for preparing nudicaulin derivatives which are structurally modified in the indole and/or the polyphenolic part of the molecule and may have optimized pharmacological activities.

Natural Products from Actinobacteria Associated with Fungus-Growing Termites.

The chemical analysis of insect-associated Actinobacteria has attracted the interest of natural product chemists in the past years as bacterial-produced metabolites are sought to be crucial for sustaining and protecting the insect host. The objective of our study was to evaluate the phylogeny and bioprospecting of Actinobacteria associated with fungus-growing termites. We characterized 97 Actinobacteria from the gut, exoskeleton, and fungus garden (comb) of the fungus-growing termite Macrotermes natalensis and used two different bioassays to assess their general antimicrobial activity. We selected two strains for chemical analysis and investigated the culture broth of the axenic strains and fungus-actinobacterium co-cultures. From these studies, we identified the previously-reported PKS-derived barceloneic acid A and the PKS-derived rubterolones. Analysis of culture broth yielded a new dichlorinated diketopiperazine derivative and two new tetracyclic lanthipeptides, named rubrominins A and B. The discussed natural products highlight that insect-associated Actinobacteria are highly prolific natural product producers yielding important chemical scaffolds urgently needed for future drug development programs.

Precursor-Directed Diversification of Cyclic Tetrapeptidic Pseudoxylallemycins.

Cyclic peptides containing non-proteinogenic amino acids often exhibit a broad bioactivity spectrum and many have entered clinical trials with good prospects for drug development. We recently reported the discovery of six cyclic tetrapeptides, pseudoxylallemycins A-F (1-6), from a termite-associated Pseudoxylaria sp. X802. These compounds contain a rare O-homoallenyl-l-tyrosine moiety and show promising antimicrobial activity against the Gram-negative pathogenic bacterium Pseudomonas aeruginosa. To perform more detailed structure-activity studies, we pursued a precursor-directed diversification strategy. Herein, we report the purification, identification, and testing of 21 new pseudoxylallemycin derivatives.

Expanding the Rubterolone Family: Intrinsic Reactivity and Directed Diversification of PKS-derived Pyrans.

We characterized two key biosynthetic intermediates of the intriguing rubterolone family (tropolone alkaloids) that contain a highly reactive pyran moiety (in equilibrium with the hydrolyzed 1,5-dione form) and undergo spontaneous pyridine formation in the presence of primary amines. We exploited the intrinsic reactivity of the pyran moiety and isolated several new rubterolone derivatives, two of which contain a unique thiazolidine moiety. Three rubterolone derivatives were chemically modified with fluorescence and biotin tags using peptide coupling and click reaction. Overall, eight derivatives were fully characterized by HRMS/MS and 1D and 2D NMR spectroscopy and their antimicrobial, cytotoxic, anti-inflammatory and antiparasitic activities evaluated.

Natural products and morphogenic activity of γ-Proteobacteria associated with the marine hydroid polyp Hydractinia echinata.

Illumina 16S rRNA gene sequencing was used to profile the associated bacterial community of the marine hydroid Hydractinia echinata, a long-standing model system in developmental biology. 56 associated bacteria were isolated and evaluated for their antimicrobial activity. Three strains were selected for further in-depth chemical analysis leading to the identification of 17 natural products. Several γ-Proteobacteria were found to induce settlement of the motile larvae, but only six isolates induced the metamorphosis to the primary polyp stage within 24h. Our study paves the way to better understand how bacterial partners contribute to protection, homeostasis and propagation of the hydroid polyp.

Isolation, Biosynthesis and Chemical Modifications of Rubterolones A-F: Rare Tropolone Alkaloids from Actinomadura sp. 5-2.

The discovery of six new, highly substituted tropolone alkaloids, rubterolones A-F, from Actinomadura sp. 5-2, isolated from the gut of the fungus-growing termite Macrotermes natalensis is reported. Rubterolones were identified by using fungus-bacteria challenge assays and a HRMS-based dereplication strategy, and characterised by NMR and HRMS analyses and by X-ray crystallography. Feeding experiments and subsequent chemical derivatisation led to a first library of rubterolone derivatives (A-L). Genome sequencing and comparative analyses revealed their putative biosynthetic pathway, which was supported by feeding experiments. This study highlights how gut microbes can present a prolific source of secondary metabolites.

A tale of four kingdoms - isoxazolin-5-one- and 3-nitropropanoic acid-derived natural products.

Covering up to September 2016This review reports on natural compounds that derive from the isoxazolinone ring as well as the 3-nitropropanoic acid (3-NPA) moiety. These structural elements occur in compounds that have been identified in plants, insects, bacteria and fungi. In particular, plants belonging to the family of legumes produce such compounds. In the case of insects, isoxazolin-5-one and 3-NPA derivatives were found in leaf beetles of the subtribe Chrysomelina. A number of these natural products have been synthesized so far. In the case of the single compound 3-NPA, several synthetic strategies have been reported and some of the most efficient routes are reviewed. The toxicity of 3-NPA results from its ability to bind covalently to the catalytic center of succinate dehydrogenase causing irreversible inhibition of mitochondrial respiration. As a motif that is produced by many species of plants, leaf beetles and fungi, different detoxification mechanisms for 3-NPA have evolved in different species. These mechanisms are based on amide formation of 3-NPA with amino acids, reduction to ß-alanine, ester formation or oxidation to malonic acid semialdehyde. The biosynthetic pathways of 3-NPA and isoxazolin-5-one moieties have been studied in fungi, plants and leaf beetles. In the case of fungi, 3-NPA derives from aspartate, while leaf beetles use essential amino acids such as valine as ultimate precursors. In the case of plants, it is supposed that malonate serves as a precursor of 3-NPA, as indicated by feeding of 14C-labeled precursors to Indigofera spicata. In other leguminous plants it is suggested that asparagine is incorporated into compounds that derive from isoxazolin-5-one, which was indicated by 14C-labeled compounds as well. In the case of leaf beetles it was demonstrated that detection of radioactivity after 14C-labeling from a few precursors is not sufficient to unravel biosynthetic pathways.

Pseudoxylallemycins A-F, Cyclic Tetrapeptides with Rare Allenyl Modifications Isolated from Pseudoxylaria sp. X802: A Competitor of Fungus-Growing Termite Cultivars.

Based on fungus-fungus pairing assays and HRMS-based dereplication strategy, six new cyclic tetrapeptides, pseudoxylallemycins A-F (1-6), were isolated from the termite-associated fungus Pseudoxylaria sp. X802. Structures were characterized using NMR spectroscopy, HRMS, and Marfey's reaction. Pseudoxylallemycins B-D (2-4) possess a rare and chemically accessible allene moiety amenable for synthetic modifications, and derivatives A-D showed antimicrobial activity against Gram-negative human-pathogenic Pseudomonas aeruginosa and antiproliferative activity against human umbilical vein endothelial cells and K-562 cell lines.

Structure and biosynthetic assembly of gulmirecins, macrolide antibiotics from the predatory bacterium Pyxidicoccus fallax.

The gulmirecins constitute a new class of glycosylated macrolides that were isolated from the predatory bacterium Pyxidicoccus fallax HKI 727. Their structures were solved by a combination of NMR spectroscopic experiments and chemical derivatization. Analysis of the annotated gulmirecin gene cluster complemented the configurational assignment and provided insights into the stereochemical course of the biosynthetic assembly. The gulmirecins exhibit strong activity against staphylococci, including methicillin-resistant Staphylococcus aureus, but no cytotoxic effects on human cells.

Laser ablation of metastatic lesions of the lung: long-term outcome.

OBJECTIVE: Pulmonary metastatic lesions are present in 20-54% of all patients who die of cancer. Surgical studies have shown that local management of distant tumor metastasis as part of multimodal cancer therapy improves survival. Minimally invasive procedures such as thermal ablation are still to prove their clinical relevance. The aim of this study was to monitor therapeutic outcome and long-term results after percutaneous laser-induced thermal ablation. SUBJECTS AND METHODS: Sixty-four patients with metastasis to the lung underwent laser-induced thermal ablation in an ongoing prospective study. A total of 129 percutaneous procedures were performed to manage a total of 108 lung lesions. The median tumor size was 2.0 cm (range, 0.4-8.5 cm). Adequate management of all known individual tumor correlates was critical for definitive patient therapy. The Kaplan-Meier method was used to calculate survival and recurrence rates. RESULTS: Definitive management of initial pulmonary disease was achieved in 31 of 64 patients. The 1-, 2-, 3-, 4-, and 5-year survival rates after ablative therapy were 81%, 59%, 44%, 44%, and 27%. The median progression-free interval was 7.4 months. There were no therapy-related deaths. Pneumothorax occurred in 38% of the patients, necessitating periprocedural drainage in 5% of all cases. Parenchymal bleeding (13% of cases) always was self-limited. CONCLUSION: Laser ablative therapy for pulmonary metastasis is a promising option in multimodal cancer therapy. The procedure is safe and effective. The initial clinical outcome data strongly suggest that this technique has the potential to improve survival among selected patients.

Non-invasive quantification of hepatic fat fraction by fast 1.0, 1.5 and 3.0 T MR imaging.

INTRODUCTION: Even mild hepatic steatosis in a split liver donor may cause general liver failure and death in the donor. So far, CT density measurements or percutaneous biopsy is used to determine the presence of hepatic steatosis. Magnetic resonance imaging (MRI) may be an elegant method of non-invasive and non-radiation quantification of hepatic fat content. METHODS: Fast gradient echo (GRE) technique was used to discriminate between fat and water spins. Echo time (TE) was adjusted for field strength dependent in-phase and out-of-phase states at 1.0, 1.5 and 3.0 T. Continuous MR signal transition from 100% water to 100% fat was investigated using a wedge water-oil phantom, which was positioned in such a way, that no spatial resolution occurred, thereby combining water and fat in one slice. RESULTS: Using the phantom, a significant difference for a 5% difference in fat content was demonstrated in the range from 20 to 80% fat content (p<0.05) for all tested field strengths. In 25 patients MRI data were correlated with the percentage of fat determined by histologic evaluation of a CT-guided liver biopsy. Using the linear correlation calculated from the MRI phantom data at 1.0 T, we determined the liver fat from each patient's MRI measurements. Comparison of these data with the histologic quantified fat fraction of liver tissue showed a strong correlation (r(2)=0.93 for TE 6 ms and r(2)=0.91 for TE 10 ms). CONCLUSION: The described method can be used to determine the presence of hepatic steatosis of >10% with p<0.05.

Maxillary sinus pneumatization of an adult skull with an untreated bilateral cleft palate.

INTRODUCTION: Patients with clefts of lip, alveolus and palate show a high incidence of maxillary sinusitis. In order to evaluate sinus size as a factor in sinusitis, this study investigates maxillary sinus morphology in an adult skull with an untreated bilateral cleft. MATERIAL AND METHODS: The maxillary sinus volume (MSV) of a mixed-sex sample of 140 adult skulls from three different populations was assessed and compared with the MSV of a skull of a 25 year old man showing an untreated complete bilateral cleft. A least squares regression analysis was used to investigate the relationship between MSV and different external cranial dimensions. RESULTS: The cleft skull shows a well-developed set of paranasal sinuses. There are close, significant relationships between MSV and the cranial measurements. The cleft skull had a MSV that does not deviate substantially from that predicted from the size of its facial skeleton. CONCLUSION: This study indicates a close link between the size of the facial skeleton and the MSV in humans, even in case of an untreated bilateral cleft. This, in conjunction with the existing literature, makes it extremely unlikely that the sizes of the paranasal sinuses are a factor for sinusitis in patients with cleft lip, alveolus and palate.

Laser ablation of lung metastases: results according to diameter and location.

Lung tumour ablation with a thin-calibre laser applicator system was evaluated. We quantified feasibility, technical success and complication rates in relation to lesion diameter and location. Forty-two patients with 64 lung tumours were treated (39 patients with metastases and three with primary tumours). Mean follow-up was 7.6 months (range 6 weeks to 39 months). Eighty-six percent of treatments were technically successful in the first session. Pneumothorax was the main complication and occurred in 50% of the first 20 patients and in 35% of the rest. Two patients required a chest tube. Fourteen lesions were central and 50 were peripheral. It took several weeks for the effect of the therapy to become apparent on follow-up CT. Thirty-nine percent of all lesions increased in size immediately after treatment. Gross reduction in size with scar formation was seen in 50% of the lesions and cavitation in 13%. Local tumour control was achieved in 51 lesions. Progression after therapy was seen in 9% of lesions <1.5 cm but in more than 11% of larger lesions. Progression was also more frequent in lesions located in the basal parts of the lung (47%). Sixteen patients died due to systemic progression. Our results suggest that successful laser ablation of lung lesions is possible with a miniaturized applicator.

Scintigraphic evaluation of jejunal interposition after distal esophageal resection for early Barrett's carcinoma.

Subtotal esophagectomy still is the major treatment for early Barrett's carcinoma. The inevitable loss of the gastric reservoir leaves an unresolved functional problem. Distal esophageal resection combined with a short jejunal interposition might be a safe alternative with the advantage of better functional results. In this series, 12 or more months after limited surgery for early Barrett's carcinoma 8 patients underwent functional investigation by alimentary scintigraphy. The activity of a technetium-labeled bolus passing through the esophagus and the jejunal interposition into the stomach was consecutively measured. Compared to 11 healthy controls the transit through the tubular esophagus showed no significant delay; transit time, however, increased with a bolus-induced dilation of the jejunal interposition. The length of the transit time through the jejunal interposition correlated with the length of the jejunal segment. The delay of bolus passage into the stomach did not result in substantial symptoms in jejunal segments shorter than 12 cm. Propulsive activity within the jejunal interposition resulted in a bolus transport into the stomach without any reflux to the esophagus. These data demonstrate good transport function and reflux prevention of short jejunal segments interposed between the esophagus and the stomach.