HRMS Methods Research Articles

The Synthesis and Characterisation of a Free‐Base Porphyrin–Perylene Dyad that Exhibits Electronic Coupling in Both the Ground and Excited States

A covalent dyad composed of a free-base porphyrin and a perylene diimide (1) was synthesised and characterised by NMR, HRMS, UV/Vis and fluorometric methods. UV/Vis spectrophotometric analysis indicated a moderate coupling between the components in the ground state. Fluorescence spectroscopy revealed that the emissive properties of the dyad showed that the quantum yield of emission from the porphyrin Soret band increased dramatically and could not be rationalised by a straightforward photoinduced energy (and/or electron) transfer, but rather a coupling of excited states.

New Diterpene Alkaloids from Aconitum sungpanense var. leucanthum

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A new diterpenoid alkaloid from a Tibetan medicinal herb Aconitum naviculare Stapf

A new diterpenoid alkaloid, named as navirine (1), was isolated along with five known alkaloids, i.e., isoatisine (2), hordenine (3), atisine (4), hetisinone (5) and delfissinol (6), from the ethanol extract of the whole plant of Tibetan medicinal plant Aconitum naviculare Stapf. The structure of the new compound was established on the basis of HR-MS, 1H, 13C and 2D NMR spectroscopic methods.

Chemical characterisation of three haemolytic compounds from the microalgal species Fibrocapsa japonica (Raphidophyceae)

The molecular structures of the three main haemolytic compounds (Fj1, Fj2 and Fj3) isolated from the ichthyotoxic microalgal species Fibrocapsa japonica have been investigated by NMR, LC–ESI–MS, ESI–MS–MS, IR, GC–MS and GC–HRMS methods. They are polyunsaturated fatty acids which we identified as: 6,9,12,15-octadecatetraenoic acid (OTA, C18:4ω3), 5,8,11,14,17-eicosapentaenoic acid (EPA, C20:5ω3) and 5,8,11,14-eicosatetraenoic acid (arachidonic acid AA, C20:4ω6). The identity of the latter two was confirmed on the basis of commercial standards (C20:5ω3 and C20:4ω6). Both displayed the same spectroscopic and chromatographic characteristics as Fj2 and Fj3 and had a similar strong haemolytic effect. We propose that when F. japonica cells accumulate in fish gills during blooms these compounds could be the cause of icthyotoxicity.

Phenolic Metabolites of Dalea versicolor that Enhance Antibiotic Activity against Model Pathogenic Bacteria

A new flavonoid (1) was isolated from organic extracts of Dalea versicolor, along with six known phenolic compounds (2-7). The structures of the seven compounds were determined by NMR and HRMS methods. These compounds were evaluated for direct activity against a variety of organisms in vitro, including the Gram-positive bacteria Staphylococcus aureus and Bacillus cereus. In addition, the compounds were evaluated for their ability to potentiate the activity of known antimicrobials through inhibition of multidrug-resistance (MDR) pumps. Compounds 1, 2, 4, and 7 exhibited direct or synergistic activity toward the human pathogen S. aureus and the opportunistic pathogen B. cereus. Compounds 4 and 7 were also found to potentiate the activity of berberine and of prescribed antibiotics, with 4 demonstrating a mode of action consistent with inhibition of the NorA MDR efflux pump in S. aureus.

New geranyl stilbenes from Dalea purpurea with in vitro opioid receptor affinity.

Three new geranyl stilbenes, pawhuskins A, B, and C (1, 2, and 3), were isolated from organic extracts of Dalea purpurea. The structures of the three compounds were determined by NMR and HRMS methods. The activities of these compounds, along with that of the known compound petalostemumol (4), were evaluated in an opioid receptor assay in vitro. Pawhuskin A (1) exhibited the strongest activity of the four compounds with a K(i) value of 0.29 +/- 0.11 microM.