Over the past years, marine microorganisms have proven to be a prolific source of structurally interesting and biologically active natural products. Marine fungi in particular have attracted considerable interest due to the diversity in chemical structures and biological activities observed for their secondary metabolites.

During our ongoing search for new bioactive metabolites from endophytic fungi with focus on the discovery of new antimicrobial compounds, we investigated the fungal strain Stemphylium globuliferum isolated from the medicinal plant Mentha pulegium (Lamiaceae). The EtOAc extract of the poorly investigated S. globuliferum fungal strain afforded six new bisanthraquinones, together with four known related compounds. All compounds were tested for their antimicrobial activity (including antibacterial, antifungal and antiviral activities). All dimers were found to be highly active at minimal inhibitory concentrations (MIC) of 7–125 µg/mL. Of specific interest is the fact that the alterporriol-type dimers, alterporriol E and its atropisomer D, exhibited different activity patterns against similar pathogenic microorganisms.

The endophytic fungus Corynespora cassiicola was isolated from the leaf tissues of the Chinese mangrove medicinal plant Laguncularia racemosa. The EtOAc extract of the fungus, which was grown on solid rice medium, exhibited considerable cytotoxic activity against Hela cell line, as well as antimicrobial activity (when tested in vitro). Chemical investigation of the extract yielded twelve new secondary metabolites, including corynecassiicol A (1) and its isomer corynecassicol B (2), corynesidone D (3), seven octalactones, coryneoctalactone A-G (4-10) and two decalactones, xestodecalactone D and E (11 and 12), together with four known compounds. The structures of the isolated compounds were determined on the basis of one- and two-dimensional NMR spectroscopy as well as mass spectrometry.

Parapiptadenia rigida (Benth.) Brenan (Fabaceae), popularly known in Brazil as „Angico vermelho“, is a perennial tree native in South America. Preparations from its bark are used in traditional medicine because of its astringent, expectorant, antiseptic and antihemorrhagic properties [1–2], but no detailed phytochemical analysis has yet been performed. To increase our knowledge on the biologically active compounds from P. rigida, the ethanolic extract of its bark was phytochemically analysed and 10 catechin derivatives were isolated and identified by 1D and 2D NMR (1H, 13C, COSY, HSQC, HMBC, NOESY, 2D-ROESY) and ESI-MS spectroscopy analyses. 3″, 4′-O-methyl-apocynin (1), 3″,4′-O-methyl-apocynin-B (2), epigallocatechin-(4β-8)-4′-O-methyl-gallocatechin (3), 4′-O-methyl-gallocatechin-(4α-8)-4′-O-methyl-gallocatechin (4) and (–)-epigallocatechin-3-O-ferulate (5) have been found for the first time and 4′-O-methyl-(–)-epigallocatechin-3-O-gallate (6) for the first time from natural sources, in addition to the four known compounds 4′-O-methyl-gallocatechin (7), 4′-O-methyl-epigallocatechin (8), 3′-O-methyl-(–)-epicatechin (9) and (–)-epigallocatechin-3-O-gallate (10). Comprehensive conformational analyses were performed for the dimeric procyanidins 3 and 4. Absolute configuration of 2 was determined by CD analysis. The extract and some of the catechin derivatives were studied for their wound healing effect in the scratch assay and gave promising results which suggest that plant preparations from P. rigida and their effective ingredients may have beneficial effects as a wound healing remedy.

A bioassay-guided investigation of a Philippine specimen of the echinoderm Comanthus parvicirrus yielded ten compounds evenly divided into anthraquinones and naphthopyrones. Four of the five anthraquinones were identified as 1′-deoxyrhodoptilometrin (2) and rhodoptilometrin (3) along with their respective 6-O-sulfate derivatives (4 and 5) in addition to a new natural anthraquinone congener (1). The isolated naphthpyrones were comaparvin (6), 6-methoxycomaparvin (7), 6-hydroxycomaparvin-8-O-sulfate (10), 6-methoxycomaparvin-5-methylether (8), and its 8-O-sulfate derivative (9). The structures of the isolated compounds were unambiguously assigned on the basis of spectroscopic methods. The absolute configuration of 3 and 5 was determined as (S)-(–) isomer. The isolated compounds were evaluated for their antibacterial, antifungal, antiviral and cytotoxic activities. In the cytotoxicity (MTT) assay against mouse lymphoma L5178Y cells, 2 and the unseparable mixture of 6 and 7 exhibited pronounced activity (IC50 values of 7.71 and 16.5 µM, respectively) compared to kahalalide F (IC50=4.3 µM) which was tested and proven to be mainly through induction of apoptosis. Moreover amongst the tested compounds for the protein kinase inhibitory activity against 24 different enzymes, anthraquinone congeners (2-5) and the unseparable naphthopyrone mixture (6/7) exhibited the most potent and selective behaviour with IC50 values between 1.8 and 33 µM. Compounds (1-3) and (6-8) were also tested for their potential to inhibit the activation of the transcription factor NF-κB, which plays an important role in cancer development and inflammation. Only naphthopyrones (6-8) significantly inhibited NF-κB activity (IC50's of 50–100 µM) and their mechanism of action was investigated.

Trypanosomiasis (also known as sleeping sickness), an important parasitic disease caused by Trypanosoma brucei, is considered as a neglected disease that reemerged over the last few decades. This fact necessitates the search and development of new drugs to target this disease. In our continuous search for new and biologically active natural products for medicinal applications or as leads for the development of new therapies, fungal endophytes have proven to be a promising vast resource of unique metabolites with great pharmacological potential. In this study we investigated an endophytic Penicillium sp. which was isolated from stem tissues of Limonium tubiflorum (Rutaceae) growing in Egypt. Chemical investigation of the fungal extract yielded four new metabolites, including a new bianthrone (1), two new curvularin derivatives (2 and 3), as well as a new sulfinylchromone (4), in addition to 13 known metabolites (5-17). All structures were assigned by comprehensive spectral analysis (1D and 2D NMR) and mass spectrometry. Some of the isolated constituents proved active against T. brucei with MIC values ranging from 4.9 to 9.7 µM.

Extracts of the fungus Stemphylium globuliferum, an endophyte of the Moroccan medicinal plant Mentha pulegium, exhibited considerable cytotoxic and antimicrobial activities when tested in vitro. Chemical investigation of the extracts yielded four new secondary metabolites, including altersolanol K (1), altersolanol L (2), altersolanol M (3), and altersolanol N (4), together with the known compounds 6-O-methylalaternin (5), macrosporin (6), altersolanol A (7), tetrahydroaltersolanol B (8), altersolanol C (9), altersolanol J (10), stemphypyrone (11) and indole-3-carboxaldehyde (12). The structures of all compounds were determined on the basis of one- and two-dimensional NMR spectroscopy and mass spectrometry. Among the altersolanol derivatives tested, compound (3) was the most active congener against L5178Y cell line with an EC50 value of 1.14 µM. Moreover, all anthraquinones exhibited antibiotic activity against several pathogenic microbes. Interestingly, the new altersolanol N together with altersolanol C showed considerable antiviral activity against HRV39, whereas tetrahydroaltersolanol B was very active against HRV2, HRV8 and HRV16.

A detailed analysis of a Philippine specimen of the marine echinoderm Comanthus sp. yielded fifteen compounds including four anthraquinones identified as 1'-deoxyrhodoptilometrin (1) along with its 6-O-sulfate derivative (3), and rhodoptilometrin (2) with its 6-O-sulfate derivative (4). In addition five naphthpyrones including comaparvin (5), 6-methoxycomaparvin (6), 6-methoxycomaparvin-5-methylether (7), 6-methoxycomaparvin-5-methylether-8-O-sulfate (8), and 6-hydroxycomaparvin-8-O-sulfate (9) were likewise isolated and identified. Further compounds include steroids and a nucleoside derivative. The structures of the isolated compounds were unambiguously elucidated based on HRESIMS analysis, 1D and 2D NMR, and by comparison with the literature. For compounds 2 and 4 the absolute configurations were identified for the first time using the Mosher reaction. Both compounds are (S)-(-) enantiomers. All isolated compounds were evaluated for their cytotoxic activities against cancer cells using the (MTT) assay and compared to the well known marine cancer drug candidate kahalalide F (EC50=6.3 µg/mL). 1'-Deoxyrhodoptilometrine (1) and an unseparable mixture of comaparvin (5) and 6-methoxycomaparvin (6) exhibited pronounced cytotoxicity against mouse lymphoma L5178Y cells with EC50 values of 2.3 and 5.2 µg/mL, respectively.

The endophytic fungus Stemphylium globuliferum was isolated from stem tissues of the Moroccan medicinal plant Mentha pulegium. Extracts of the fungus, which was grown on solid rice medium, exhibited considerable cytotoxicity when tested in vitro against L5178Y cells. Chemical investigation yielded eight new secondary metabolites, alterporriol F, alterporriol G and its atropisomer H, alterporriol I and its atropisomer J, altersolanol K, altersolanol L and stemphypyrone, beside eight known compounds. The structures were determined on the basis of one- and two-dimensional NMR spectroscopy and mass spectrometry. Among the alterporriol-type anthranoid dimers, the mixture of alterporriols G and H exhibited considerable cytotoxicity against L5178Y cells with an EC50 value of 2.7 µg/mL, whereas the other congeners showed only modest activity. The compounds were also tested for protein kinase inhibitory activity in an assay involving 24 different kinases. Compounds methylalaternin, macrosporin, altersolanol A and the mixture of alterporriol G and H were the most potent and also selective inhibitors, displaying EC50 values between 0.64 and 1.4 µg/mL toward individual kinases.

Protein kinases, which function as components of signal transduction pathways, play a central role in diverse biological processes, such as control of cell growth, metabolism, differentiation, and apoptosis [1]. Identification of the key roles of protein kinases in cancer has led to extensive efforts to develop kinase inhibitors for the treatment of a wide range of cancers [2]. In continuation of our efforts to discover natural protein kinase inhibitors we studied extracts of liquid and rice cultures of the fungal endophyte Alternaria sp. isolated from the Egyptian medicinal plant Polygonum senegalense. Chromatographic separation of the extracts yielded the known compounds alternariol (1), alternariol 5-O-methyl ether (2), altenusin (3), 2,5-dimethyl-7-hydroxychromone (4), tenuazonic acid (5), altertoxin I (6), talaroflavone (7), and altenuene (8), in addition to seven new metabolites (9–15). The structures of the compounds were unambiguously established on the basis of NMR spectroscopic and mass spectrometric data. Compounds 1–3, 9, and 12 showed cytotoxic activity toward L5178Y mouse lymphoma cell line with EC50 values ranging from 1.7 to 7.8µg/mL. When analyzed in vitro for their inhibitory potential against 24 different protein kinases, compounds 1–3, 6, 9, and 11–13 inhibited several of these enzymes (IC50 values 0.22–9.8µg/mL).

Scorzonera radiata occurs in the mountainous regions of Mongolia. The root part is used in Mongolian traditional medicine for the treatment of many diseases, such as for curing fever, carbuncle, and mastitis. An extract of the aerial parts of the Mongolian medicinal plant Scorzonera radiata afforded two new stilbenes, as well as 13 known compounds including three flavones and nine phenolic acid compounds. Six of the phenolic compounds are quinic acid congeners. The structures of the isolated compounds were clearly elucidated on the basis of NMR (1H, 13C, COSY, HMBC), mass spectrometric data and chemical methods. The biological activities of the new stilbene derivatives 1 and 2 have been assessed. Compound 1 exhibited higher antioxidative activity in the DPPH assay when compared to its dimethoxylated congener. However, both compounds did not show any cytotoxicity towards L5178Y mouse lymphoma cell line.

In this study we investigated the natural products produced by a hitherto undescribed endophytic fungal strain of the genus Alternaria when grown in liquid medium and on solid rice medium. From extracts of the fungus grown in liquid culture we obtained new sulphated derivatives of alternariol (1) and its monomethyl ether (2) as well as the known compounds alternariol and its monomethyl ether, altenusin, 2,5-dimethyl-7-hydroxychromone, tenuazonic acid and altertoxin I. When grown on solid rice medium the fungus yielded four new compounds (3–6) in addition to alternariol and its monomethyl ether, altenusin, talaroflavone and altenuene. Furthermore, we isolated a new altenuene isomer that was given the trivial name 4'-epialtenuene (7). The structures of the compounds were unambiguously established on the basis of NMR spectroscopic and mass spectrometric data. The crude extracts and the isolated compounds exhibited moderate to strong toxicity toward L5178Y (mouse lymphoma) cell line. Altenusin, alternariol and its monomethyl ether were also unambiguously identified in Polygonum senegalense thereby proving that this fungal endophyte contributes to the chemical composition of the host plant.

In the last decades interest in the group of flavonoids has markedly increased due to their presumed beneficial effects in humans. Many flavonoids act as radical scavengers and are suggested to prevent chronic diseases such as atherosclerosis or even cancer [1]. For a critical evaluation of the effects of flavonoids with regard to human health, quantitative (daily intake as part of diet or as food supplements) as well as qualitative (structural) aspects have to be taken into consideration [2]. As part of a broader Sino-German project on flavonoids from plants used for human consumption, we analyzed four different cultivars of Vigna angularis (Willd.) Ohwi & H. Ohashi, two of them growing in China (Hangzhou) and the other two cultivated in Germany (Düsseldorf). All analyzed plants yielded catechin, myricetin–3-O–rutinoside, and rutin as main compounds but differed with regard to their total flavonoid concentrations which were lower in the Chinese cultivars. We analyzed pharmacological effects of these compounds focussing mainly on their antioxidative properties. All flavonoids exhibited a good radical scavenger activity in a cell free system (DPPH assay). In different cellular systems (rat H4IIE hepatoma and C6 glioma cells) we further analyzed protective effects of these substances against oxidative stress using the fluorescent probe DCF. Beside these antioxidative effects, cytotoxic and pro-apoptotic activities of these compounds were also determined. In consideration of these data it can be emphasized that a known composition of flavonoids is necessary in nutrient uptake.

Marine natural products with their unique structural features and pronounced biological activities continue to provide lead structures in the search for new drugs from nature. Invertebrates such as sponges, tunicates, mollusks and others that are either sessile or slow moving and mostly lack morphological defense structures have so far provided the largest number of marine-derived secondary constituents including some of the most interesting drug candidates. This review highlights recent research findings of our group related to natural products from marine invertebrates. Areas that are covered include ecological functions of secondary constituents from sponges against predatory fish, the search for new pharmacologically active constituents from sponges and tunicates, and sponge-associated fungi as an evolving source for new bioactive natural products.

This review article presents our group's recent research findings with regard to bioactive natural products from marine sponges and tunicates, as well as from sponge-derived fungi. The organisms discussed originate in the Indopacific region, which has an exceptionally rich marine biodiversity. Major topics that are covered in our review include the chemical ecology of sponges, focusing on defense against fishes, as well as the isolation and identification of new bioactive constituents from sponges and tunicates. Sponge-derived fungi are introduced as an emerging source for new bioactive metabolites, reflecting the currently growing interest in natural products from marine microorganisms.

Bioassay-guided fractionation of organic extracts of Cladosporium herbarum, isolated from the marine sponge Callyspongia aerizusa, yielded two new macrolide metabolites: pandangolide 3 and 4 (1 and 2) and the known fungal metabolites pandangolide 2 (3), cladospolide B (4), and iso-cladospolide B (5). Also isolated were the antimicrobially active (against Bacillus subtilis and Staphylococcus aureus) furan carboxylic acids: Sumiki's acid (6) and its new derivative, acetyl Sumiki's acid (7). All structures were elucidated by spectroscopic methods.

A marine soft coral species of the genus Heteroxenia collected from Mindoro Island, Philippines yielded two cadinene sesquiterpenes, (+)-alpha-muurolene (1) and a novel derivative (+)6-hydroxy-alpha-muurolene (2), as well as the biologically active polyhydroxysterol, sarcoaldosterol A (3). The structure of the novel compound was unambiguously established on the basis of NMR spectroscopic ((1)H,(13)C, COSY,(1)H-detected direct and long range (13)C-(1)H correlations) and mass spectrometric (EIMS) data. All compounds were active against the phytopathogenic fungus Cladosporium cucumerinum. The isolated terpenes were also active in the brine shrimp lethality test.

Bark of Aglaia spectabilis collected on the island of Phu Quoc (Vietnam) yielded insecticidal cyclopentatetrahydrobenzofurans of the rocaglamide type including four new natural products. Structure elucidation of the new compounds is described. All rocaglamide derivatives isolated exhibited strong insecticidal activity towards neonate larvae of the polyphagous pest insect Spodoptera littoralis when incorporated into an artificial diet. LC50 values varied from 0.8 to 80 ppm. The most active compounds isolated, methylrocaglate and C-3' hydroxylmethylrocaglate, were similar with regard to their insecticidal activity to the well-known natural insecticide azadirachtin.

Abstract From the marine sponge Callyspongia aerizusa collected from the Sea of Bali, Indonesia, fungal isolates of Drechslera hawaiiensis were obtained. Culture filtrates of the fungus yielded four spiciferone derivatives which include spiciferone A (1) and B (2), and two other novel derivatives including spiciferol A (3) which is an alcohol congener of spiciferone A (1) and compound 4 which is an monocyclic spiciferone congener featuring a butoxyl side chain. The structures of the novel compounds were established on the basis of NMR spectroscopic (1H ,13C, COSY) and mass spectrometric (EIMS) data.

Organic extracts of the twigs and leaves of Aglaia odorata yielded eight insecticidal cyclopentatetrahydrobenzofuran rocaglamide derivatives including three congeners which proved to be new natural products. Moreover, four new cyclopentatetrahydrobenzopyran aglain derivatives, as well as the known aminopyrrolidine odorine and odorinol, syringaresinol and flavonoid derivatives were also isolated. Structure elucidation of the new compounds is described and a rationale of the biosynthesis of the rocaglamide and aglain congeners is considered. The isolated rocaglamide derivatives exhibited strong insecticidal activity towards neonate larvae of the polyphagous pest insect Spodoptera littoralis when incorporated into artificial diet with LC50 values varying from 1.0–8.0 ppm. The most active compounds showed LC50 values between 1.0 and 1.1 ppm, comparable to those of the insecticide azadirachtin, which was used as a positive control. The remaining compounds isolated from A. odorata were inactive with regard to insecticidal activity.