Michael Wohlfarth

Droserone from cell cultures of Triphyophyllum peltatum (Dioncophyllaceae) and its biosynthetic origin.

The growth and droserone content of callus cultures of Triphyophyllum peltatum grown in liquid 1/5 Linsmaier and Skoog medium was studied. During a lag phase in growth, droserone concentrations in the medium reached a value of 2.1 mg g-1 fr. wt. After this maximum value the concentration decreased slightly to 1.8 mg g-1 fr. wt., while the growth of the calli was enhanced (25% increase in fr. wt. within 7 days). Plumbagin and isoshinanolone were likewise present in the medium. By feeding 13C2-labelled acetate to the cultures the biosynthesis of droserone was elucidated. The incorporation of whole C2-units unambiguously shows its acetogenic origin and fits well in the biosynthetic scheme suggested for the structurally--and biogenetically--related naphthylisoquinoline alkaloids.

The polyketide folding mode in the biogenesis of isoshinanolone and plumbagin from Ancistrocladus heyneanus (Ancistrocladaceae)

Abstract The biosynthetic orgins of the tetralone isoshinanolone and the related naphthoquinone plumbagin were investigated by feeding [13C2]-acetate to suspended callus cultures of Ancistrocladus heyneanus. The orientation of the acetate subunits was elucidated by a similar experiment using [2-13C]-acetate. The polyketide folding mode found for isoshinanolone and plumbagin constitutes a further hint at the acetogenic nature of the naphthylisoquinoline alkaloids, which are typical of A. heyneanus and other species of Ancistrocladaceae and Dioncophyllaceae.

Revised Structure of Antidesmone, an Unusual Alkaloid from Tropical Antidesma Plants (Euphorbiaceae)

Abstract The structure of antidesmone, an alkaloid from Antidesma membranaceum Mull. Arg. and A. venosum E. Mey. (Euphorbiaceae), was revised to be (S)-4,8-dioxo-3-methoxy-2-methyl-5-n-octyl-1,4,5,6,7,8-hexahydroquinoline [(S)-2], not the isoquinoline derivative 1, as assumed previously. The revision was initiated by biosynthetic feeding experiments of one of our groups.

Observation of exchangeable protons by high-performance liquid chromatography–nuclear magnetic resonance spectroscopy and high-performance liquid chromatography–electrospray ionization mass spectrometry: a useful tool for the hyphenated analysis of natural products ☆

The first high-performance liquid chromatography-nuclear magnetic resonance (HPLC-NMR) investigation of exchangeable protons of low-molecular-mass natural products is reported. Model alkaloids or crude plant extracts were dissolved in 2H2O-1H2O-MeCN (deuterium oxide-water-acetonitrile) or 2H2O-MeCN and, after direct injection or chromatographic separation, examined in a 60-microl NMR flow probe. Exchangeable amino protons initially detected by HPLC-electrospray ionization mass spectrometry were subsequently identified and investigated by stop-flow 1H-NMR, two-dimensional (2D) total correlation spectroscopy (TOCSY), and 2D nuclear Overhauser effect spectroscopy (NOESY). These experiments extend the applicability of HPLC-NMR for the investigation and structure elucidation of natural products.

Jozipeltine A, a Novel, Unnatural Dimer of the Highly Hydroxylated Naphthylisoquinoline Alkaloid Dioncopeltine A

Abstract The synthesis of jozipeltine A (5), the 6′-coupled constitutionally symmetric dimer of the highly antimalarial naphthylisoquinoline alkaloid dioncopeltine A (4), is described. After selective protection of two of the four OH- and NH-functionalities of 4, the coupling succeeds oxidatively, with Ag2O as the reagent. Deprotection gives the target molecule 5, in only three steps from 4. Jozipeltine A is the first naphthylisoquinoline dimer with oxygen functions in the side chain of the naphthalene part. Investigations on its antiplasmodial and antiviral activities provide valuable insight into structure–activity relationships within this promising class of bioactive quateraryls.

Characterization of protein mixtures by ion-exchange chromatography coupled on-line to nuclear magnetic resonance spectroscopy

Abstract The first example of HPLC–NMR analysis of proteins is reported. By this means, a mixture of hen egg lysozyme and horse heart cytochrome was separated and identified. The chromatographic separation is based on ion-exchange HPLC, which is likewise for the first time coupled to 1 H NMR. In the stop-flow mode, characteristic one-dimensional 1 H spectra, two-dimensional total correlation data sets (TOCSY), and nuclear overhauser effect correlation spectra (NOESY) of the two proteins were obtained. In addition, lysozyme from crude hen egg white was unambiguously characterized by using a stop-flow HPLC–NMR-TOCSY experiment. These experiments extend the applicability of HPLC–NMR to the rapid analysis of protein mixtures.