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Publications
Four β-carboline alkaloids, brunneins A–C (1–3) and 3-(7-hydroxy-9H-β-carboline-1-yl)propanoic acid (4), were isolated from fruiting bodies of the agaricoid fungus Cortinarius brunneus. The structures of 1–3 were determined by analysis of NMR and MS data, and the structure of compound 4 was determined by comparison with published data. Brunnein A (1) exhibited very low cholinesterase inhibitory effects and no cytotoxicity.
Publications
Plumbago indica L. contains naphthoquinones that are derived from six acetate units. To characterize the enzyme catalyzing the first step in the biosynthesis of these metabolites, a cDNA encoding a type III polyketide synthase (PKS) was isolated from roots of P. indica. The translated polypeptide shared 47–60% identical residues with PKSs from other plant species. Recombinant P. indica PKS expressed in Escherichia coli accepted acetyl‐CoA as starter and carried out five decarboxylative condensations with malonyl coenzyme A (‐CoA). The resulting hexaketide was not folded into a naphthalene derivative. Instead, an α‐pyrone, 6‐(2′,4′‐dihydroxy‐6′‐methylphenyl)‐4‐hydroxy‐2‐pyrone, was produced. In addition, formation of α‐pyrones with linear keto side chains derived from three to six acetate units was observed. As phenylpyrones could not be detected in P. indica roots, we propose that the novel PKS is involved in the biosynthesis of naphthoquinones, and additional cofactors are probably required for the biosynthesis of these secondary metabolites in vivo.
Publications
Papaver alkaloids play a major role in medicine and pharmacy. In this study, [ring-13C6]-tyramine as a biogenetic precursor of these alkaloids was fed to Papaver somniferum seedlings. The alkaloid pattern was elucidated both by direct infusion high-resolution ESI-FT-ICR mass spectrometry and liquid chromatography/electrospray tandem mass spectrometry. Thus, based on this procedure, the structure of about 20 alkaloids displaying an incorporation of the labeled tyramine could be elucidated. These alkaloids belong to different classes, e.g. morphinan, benzylisoquinoline, protoberberine, benzo[c]phenanthridine, phthalide isoquinoline and protopine. The valuable information gained from the alkaloid profile demonstrates that the combination of these two spectrometric methods represents a powerful tool for evaluating biochemical pathways and facilitates the study of the flux of distant precursors into these natural products.
Publications
Two new triterpenoids, named gouanic acid A (1) and gouanic acid B (2), were isolated from the aerial parts of Gouania ulmifolia, along with six known compounds. The structures of the new compounds were determined by spectroscopic methods, mainly NMR (1D and 2D) and mass spectrometry. The new compounds did not show significant antimicrobial activities.
Publications
A new cardenolide, 17β-H-periplogenin-3-O-β-d-digitoxoside (1), and a new pregnane glycoside, Δ5-pregnene-3β,16α-diol-d-O-[2,4-O-diacetyl-β-digitalopyranosyl-(1 → 4)-β-d-cymaropyranoside]-16-O-[β-d-glucopyranoside] (2) were isolated from the roots of Streptocaulon tomentosum (Asclepiadaceae) together with a series of known compounds. Their chemotaxonomic significance for the separation of S. tomentosum from Streptocaulon juventas is discussed, suggesting a rather clear distinction of these species.
Publications
The naphthalene-like smell of Scytinostroma portentosum (Berk. & Curt.) Donk originates predominantly from indole (1) together with 3-chloroindole (3) and to a lesser extent of 1-octen-3-ol (9). Naphthalene (8) itself could not be detected.