Norbert Arnold

Isolation of a New Natural Product and Cytotoxic and Antimicrobial Activities of Extracts from Fungi of Indonesian Marine Habitats

In the search for bioactive compounds, 11 fungal strains were isolated from Indonesian marine habitats. Ethyl acetate extracts of their culture broth were tested for cytotoxic activity against a urinary bladder carcinoma cell line and for antifungal and antibacterial activities against fish and human pathogenic bacteria as well as against plant and human pathogenic fungi. The crude extract of a sterile algicolous fungus (KT31), isolated from the red seaweed Kappaphycus alvarezii (Doty) Doty ex P.C. Silva exhibited potent cytotoxic activity with an IC50 value of 1.5 μg/mL. Another fungal strain (KT29) displayed fungicidal properties against the plant pathogenic fungus Cladosporium cucumerinum Ell. et Arth. at 50 μg/spot. 2-Carboxy-8-methoxy-naphthalene-1-ol (1) could be isolated as a new natural product.

Acetylcholinesterase inhibitors from the toadstool Cortinarius infractus.

Inhibition of acetylcholinesterase (AChE) and therefore prevention of acetylcholine degradation is one of the most accepted therapy opportunities for Alzheimer s disease (AD), today. Due to lack of selectivity of AChE inhibitor drugs on the market, AD-patients suffer from side effects like nausea or vomiting. In the present study the isolation of two alkaloids, infractopicrin (1) and 10-hydroxy-infractopicrin (2), from Cortinarius infractus Berk. (Cortinariaceae) is presented. Both compounds show AChE-inhibiting activity and possess a higher selectivity than galanthamine. Docking studies show that lacking pi-pi-interactions in butyrylcholinesterase (BChE) are responsible for selectivity. Studies on other AD pathology related targets show an inhibitory effect of both compounds on self-aggregation of Abeta-peptides but not on AChE induced Abeta-peptide aggregation. Low cytotoxicity as well as calculated pharmacokinetic data suggest that the natural products could be useful candidates for further drug development.

(Iso)-Quinoline Alkaloids from Fungal Fruiting Bodies of Cortinarius subtortus

Chemical analysis of the fruiting bodies of the agaricoid fungus Cortinarius subtortus yielded three new natural products, two quinoline and one isocarbostyryl alkaloid. The structures of compounds 1- 3 were determined by analysis of NMR and MS data. Compound 1 exhibited inhibitory effects against the phytopathogenic fungus Colletotrichum coccodes. All three compounds displayed moderate antioxidant activity in a DPPH free radical scavenging bioassay.

RDC-Based Determination of the Relative Configuration of the Fungicidal Cyclopentenone 4,6-Diacetylhygrophorone A12

The hygrophorones, a class of cyclopentenones isolated from fruiting bodies of the genus Hygrophorus (basidiomycetes), show promising antifungal activity. While the constitution of 4,6-diacetylhygrophorone A(12) (3) and the relative configuration of the stereogenic centers in the cyclopentenone ring were elucidated using standard NMR and MS techniques, the relative configuration of the exocyclic stereogenic center could not be assigned. By introducing a sample of 3 into an alignment medium and measuring anisotropic NMR parameters, namely, residual dipolar couplings, we were able to unambiguously determine the relative configuration of all three stereogenic centers in 4,6-diacetylhygrophorone A(12) simultaneously by fitting several structure proposals to the experimental data.

Antioomycete activity of γ-Oxocrotonate fatty acids against P. infestans.

Infections with Phytophthora infestans, the causal agent of potato and tomato late blight disease, are difficult to control and can lead to considerable agricultural losses. Thus, the development of new effective agents against the pathogen is of great interest. In previous work, (E)-4-oxohexadec-2-enoic acid (3) was isolated from Hygrophorus eburneus, which exhibited fungicidal activity against Cladosporium cucumerinum. Here, the inhibitory effect of 3 on P. infestans spore germination and mycelium growth in vitro is demonstrated. The in vivo effect on infections of whole potato plants was investigated by spraying plants with the sodium salt of 3, sodium (2E)-4-oxohexadec-2-enoic acid (4), prior to P. infestans inoculation. Additionally, the influence of 3 on mycelium growth of Colletotrichum coccodes, the causal agent of potato black dot disease, was analyzed. In all approaches, a significant inhibition of pathogen development was achieved. Importantly, the unsaturated fatty acid exerted no toxic effect when sprayed on plants, a prerequisite for its commercial use.

1-O-Substituted derivatives of murrayafoline A and their antifungal properties

The synthesis of some 1-oxygenated derivatives of murrayafoline A (1) and their antifungal properties is reported. Three derivatives, 1-hydroxy-3-methyl-9H-carbazole (2), 1-(3-methylbut-2-enyloxy)-3-methyl-9H-carbazole (3) and 1-(2,3,4,6-tetra-O-acetyl-α-D-O-glucopyranosyl)-3-methyl-9H-carbazole (4) of murrayafoline A were synthesized. Compounds 1 and 2 exhibited strong fungicidal activity against Cladosporium cucumerinum at the dose of 12.5 µg.

Characterization of Constituents and Anthelmintic Properties of Hagenia abyssinica

The dried female flowers of Hagenia abyssinica (Bruce) J. F. Gmel. (Rosaceae) are traditionally used as an anthelmintic remedy in Ethiopia and formerly were incorporated into the European Pharmacopoeia. One-, two- and tricyclic phloroglucinol derivatives (kosins) were suggested to be the active principles. However, polar constituents may also contribute to the activity. Therefore, we investigated for the first time the polar constituents. We isolated typical Rosaceae constituents such as quercetin 3-O-β-glucuronide, quercetin 3-O-β-glucoside and rutin. Polar kosin glycosides or derivatives could not be detected. The anthelmintic activity of fractions of different polarity were tested against the blood fluke Schistosoma mansoni, the liver flukes Clonorchis sinensis and Fasciola hepatica and the intestinal fluke Echinostoma caproni. The anthelmintic activity decreased with increasing polarity of the tested fractions. ESI-MS investigations indicated the predominant occurrence of kosins in the active fractions. Using the anthelmintic active extracts of Hagenia abyssinica we developed a simple, inexpensive bioassay against the non-parasitic nematode Caenorhabditis elegans, which can be used as an initial screening procedure for anthelmintic properties of crude extracts of plants or fungi. The anthelmintic activity of test extracts against the model organism was determined in a microtiter plate assay by enumeration of living and dead nematodes under a microscope.

Penarines A–F, (nor-)sesquiterpene carboxylic acids from Hygrophorus penarius (Basidiomycetes)

Five sesquiterpene carboxylic acids (1-5) and one nor-sesquiterpene carboxylic acid (6) of the very rare ventricosane type, named penarines A-F, were isolated from fruiting bodies of the basidiomycete Hygrophorus penarius (Hygrophoraceae). This is the first report of (nor)-sesquiterpenes isolated from basidiocarps of the family Hygrophoraceae. Their structures were elucidated on the basis of extensive 1D ((1)H, (13)C) and 2D (HSQC, HMBC, COSY, ROESY) NMR spectroscopic analyses as well as high-resolution mass spectrometry studies. Additionally, the only known member of this rare type of sesquiterpenes, ventricos-7(13)-ene (7), could be identified via headspace GC-MS analysis in a fruiting body of H. penarius. Compounds 1-6 were devoid of remarkable antifungal activity against Cladosporium cucumerinum. Additionally, the cytotoxic activities of compounds 1 and 2 were evaluated against the human prostate cancer cell line PC-3 and the colon cancer cell line HT-29 showing no significant cytotoxic activity.

Determination of β‐carboline alkaloids in fruiting bodies of Hygrophorus spp. by liquid chromatography/electrospray ionisation tandem mass spectrometry

The beta-carboline alkaloids harmane (1) and norharmane (2) were isolated from fruiting bodies of Hygrophorus eburneus (Bull.) Fr. as well as brunnein A (3) from Hygrophorus hyacinthinus Quél. (Tricholomataceae, Agaricales) for the first time. Their occurrence within the genus was investigated using liquid chromatography/electrospray ionisation tandem mass spectrometric methods, especially by selected reaction monitoring. Based on these results their chemotaxonomical relevance is discussed.

N-Glucosyl-1H-indole Derivatives from Cortinarius brunneus (Basidiomycetes)

Two new N‐glucosylated indole alkaloids were isolated from fruiting bodies of the basidiomycete Cortinarius brunneus (Pers.) Fr. The structures were elucidated by means of the spectroscopic data. Additionally, the very recently reported compounds N‐1‐β‐glucopyranosyl‐3‐(carboxymethyl)‐1H‐indole (3) and N‐1‐β‐glucopyranosyl‐3‐(2‐methoxy‐2‐oxoethyl)‐1H‐indole (4) could be detected. Compound 3 is the N‐glucoside of the plant‐growth regulator 1H‐indole‐3‐acetic acid (IAA), but, in contrast, it does not exhibit auxin‐like activity in an Arabidopsis thaliana tap root elongation assay.