Per Halfdan Nielsen

Structure of red and orange fluorescein

The structures of colorless, red, and yellow-orange fluorescein have been investigated by a combination of solution and solid state13C NMR. It is demonstrated that the three forms have lactonic, zwitterionic, and quinoid structures, respectively. Conflicting X-ray, NMR, and IR structural evidence is discussed for samples of red fluorescein which cannot readily be obtained in definite crystalline form. It is concluded that solid-state13C NMR spectroscopy is superior by revealing primarily the molecular structure but being fairly insensitive toward lattice variations.

Antibacterial activity of marine-derived fungi

A total of 227 marine isolates of ubiqituous fungi were cultivated on different media and the secondary metabolite content of the extracts (ethyl acetate/chloroform/methanol 3 : 2 : 1) characterized by HPLC. The fungi were secured from animals, plants and sediments of Venezuelan waters (0–10 m) including mangroves and lagoonal areas. The extracts were tested for antibacterial activity. A total of 7 were active towards Vibrio parahaemolyticus and 55 towards Staphylococcus aureus, representing 18 different fungal species from 8 ascomycetous genera. For 61 strains of Penicillium citrinum antibacterial activity correlated well with content of secondary metabolites as measured by HPLC. Thirteen isolates of Penicillium steckii produced very similar profiles of secondary metabolites and 6 of these had activity against either V. parahaemolyticus or S. aureus or both.

Fungal depside, guisinol, from a marine derived strain of Emericella unguis

Abstract A marine isolate of the fungus Emericella unguis gave a new antibacterial depside, guisinol (1). The structure determination was based on mass spectrometry and NMR spectroscopical studies. Structurally 1 resembles the depsidones emeguisin A→C previously isolated from another strain of the same species. Five other isolates of E. unguis also produced the same qualitative profile of secondary metabolites including guisinol and dechloronidulin. Other species of Emericella did not produce any of these compounds and they are thus of chemotaxonomic significance.

Seasonal variation and distribution of two phenolic compounds, rosmarinic acid and caffeic acid, in leaves and roots-rhizomes of eelgrass (Zostera Marina L.)

Abstract The seasonal variation and distribution of rosmarinic acid and caffeic acid in leaves and roots-rhizomes of eelgrass (Zostera marina L.) were examined by using an isocratic high-performance liquid chromatography (HPLC) method developed for separation and quantification of the two phenolic compounds in crude plant extracts. The variation in phenolic content was compared to variations in tissue concentrations of nitrogen and phosphorus, in order to test a proposed relationship between nutrient status of the plant and biosynthesis of the secondary metabolites. The concentration of rosmarinic acid (not previously found in a monocotyledon) plus caffeic acid ranged from 0.4 to 19.2 mg (g dw)-1 with rosmarinic acid being the quantitatively most important component. The figures represent low estimates due to loss of phenolics during sample preparation. High phenolic concentrations occurred in spring and low concentrations during summer and fall, and the highest concentrations were most often found in the...

Bryozoan secondary metabolites : a chemotaxonomical challenge

Abstract 1. 1. A survey of the literature shows that microorganisms are found to be present in several species of unrelated bryozoans (syn. ectoprocts). 2. 2. The occurrence and chemical structure of secondary metabolites in bryozoans are discussed. 3. 3. The possibility of a dietary vs a microbial origin of the secondary metabolites is discussed. 4. 4. A hypothesis is proposed that some of the secondary metabolites isolated from bryozoans are synthesized by associated microorganisms.

Standardized extraction method for paralytic shellfish toxins in phytoplankton

The optimal conditions were established for extraction of paralytic shellfish toxins from a Danish clone of Alexandrium tamarense using extraction with acetic acid and HCl in the concentration range 0.01–1.0 N. Physical destruction of the cells was investigated microscopically to select the most efficient extraction procedure.The toxin content was quantitated by an automized isocratic reversed-phase high-performance liquid chromatography (HPLC) method. The best results as judged from the total amount of toxins and the toxin profile were obtained using 0.05–1.0 N acetic acid and 0.01–0.02 N HCl. Hydrochloric acid in the concentration range 0.03–1.0 N caused the amount of C1 and C2 toxins to decrease sharply and concomitant increase of gonyautoxins 2 and 3.The phytoplankton extracts with 0.1 to 0.5 N acetic acid or 0.01 N HCl were stable during 6 months at −20 °C, but the extracts with HCl 0.02 N underwent a change in toxin profile, although the total amount of toxins was constant.

Dipodazine, a diketopiperazine from Penicillium dipodomyis

Abstract Dipodazine, ( Z )-1′,3-didehydro-3-(3″-indolylmethylene)-piperazine-2,5-dione ( 1 ), has been isolated from Penicillium dipodomyis and is also present in P. nalgiovense . The structure was established by spectroscopical methods.

Eleganolone derived diterpenes from Bifurcaria bifurcata

Abstract Three new diterpenes were isolated from the brown alga Bifurcaria bifurcata together with elegandiol and eleganolone. The new compounds are all formally derived from eleganolone. This is the first report on cyclic diterpenoids from Bifurcaria . The structures were established by spectroscopic methods.

Unguisin C, a GABA-containing cyclic peptide from the fungus Emericella unguis.

Besides the known unguisins A and B, a new cyclic heptapeptide, unguisin C, containing a GABA-derived moiety in the ring, was isolated from the fungus Emericella unguis. The structure was determined by 1D and 2D NMR techniques. Marfeys method was used to determine the absolute stereochemistry. Precursor-directed biosynthesis of the unguisins was performed by supplementation of the culture medium with amino acids (L-Ala, L-Ser, L-Phe and L-Leu). A related cyclic heptapeptide, unguisin D, was detected by HPLC and characterized by sequence analysis using LC-QITMS.

Is trimethylamine oxide a reliable indicator for the marine origin of fish

Abstract 1. 1. The non-protein nitrogen fraction of four fish species from Lake Victoria was investigated. 2. 2. The presence of content of trimethylamine oxide (TMAO) was determined by the Conway microdiffusion assay and confirmed by 1 H and 13 C NMR spectroscopy and FAB mass spectrometry. 3. 3. Nile perch ( Lates niloticus ) and a Tilapia sp. contained exceptionally high levels of TMAO (150–200 mg/100 g) for freshwater fish species. 4. 4. TMAO was not present in the catfish Bagrus and Clarias from the same area. 5. 5. Concentrations of free amino acids were 2700–5000 μmol/100 g with taurine accounting for 50–75% of the free amino acids.