Markus Rückert

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.

Ancistrobertsonines b, C, and D as well as 1,2-didehydroancistrobertsonine D from Ancistrocladus robertsoniorum

Abstract From the East African Liana Ancistrocladus robertsoniorum , four new naphthylisoquinoline alkaloids have been isolated using High Speed Countercurrent Chromatography (HSCCC) and High Performance Liquid Chromatography (HPLC). Their stereostructures were established by spectroscopic, chemical, and chiroptical methods. Two of the new compounds, ancistrobertsonines B and C, constitute O - and N -permethylated 5,1′-coupled and 5,8′-coupled regioisomeric naphthylisoquinolines, while ancistrobertsonine D and its 1,2-didehydro analogue are based on a 7,1′-coupling mode between the isoquinoline and naphthalene moieties. Biological tests revealed that some of the isolated alkaloids possess moderate antimalarial activities.

Acetogenic isoquinoline alkaloids: CXXI. Use of on-line high-performance liquid chromatography–nuclear magnetic resonance spectrometry coupling in phytochemical screening studies: rapid identification of metabolites in Dioncophyllum thollonii

Abstract Exemplarily for a root extract of the West African liana Dioncophyllum thollonii a strategy for the rapid identification of secondary metabolites in plant extracts is presented, based upon on-line coupling of high-performance liquid chromatography with nuclear magnetic resonance detection. For a first overview, an on-flow experiment was performed, which allowed the identification of the naphthylisoquinoline alkaloid dioncophylline A. A second alkaloid, 5′-O-demethyldioncophylline A, was identified by subsequent application of stop-flow two-dimensional HPLC–NMR ROESY experiments. In the case of coeluting compounds, the design of appropriate time-slice experiments allowed the characterization of the diastereomeric tetralones trans- and cis-isoshinanolone. Thus, through consequent use of all different experimental modes available in HPLC–NMR, a phytochemical screening of plant extracts can be realized in a fast and reliable way. The NMR detection allows the characterization of diastereomeric compounds even in the case of far-reaching chromatographic coelution.

Characterization of metabolites in plant extracts of Ancistrocladus likoko by high-performance liquid chromatography coupled on-line with 1H NMR spectroscopy†‡

One‐ and two‐dimensional stop‐flow HPLC–NMR experiments were applied to investigate a root extract of Ancistrocladus likoko (Ancistrocladaceae). Three new naphthylisoquinoline alkaloids with a 5,8′ coupling pattern were found. The constitutions and relative configurations were elucidated by application of H,H‐TOCSY and ROESY experiments carried out in the stop‐flow mode. This example demonstrates the potential of HPLC‐NMR as an efficient coupling technique for plant screening studies in phytochemical analysis. Copyright

Dioncophylline D and 8-O-Methyldioncophylline D, 7,8′-Coupled naphthylisoquinoline alkaloids from triphyophyllum PELTATUM

Abstract Theisolation and structural elucidation of two novel naphthylisoquinoline alkaloids, dioncophylline D and its 8- O -methyl analogue, from the West African liana Triphyophyllum peltatum are described. Their structures are based on the rare 7,8′-coupling between the two molecular moieties. The absolute configuration at the stereocentres of the isoquinoline half was established by oxidative degradation to give R -3-aminobutyric acid and d -alanine. Both alkaloids are characterized by a rapid rotation around the biaryl axis. The two new alkaloids are apparently found in young (carnivorous) plants, exclusively.

Acetogenic isoquinoline alkaloids. CXII. Separation and identification of dimeric naphthylisoquinoline alkaloids by liquid chromatography coupled to electrospray ionization mass spectrometry

The atropodiastereomeric dimeric naphthylisoquinoline alkaloids, michellamines A (1a), B (1b) and C (1c), together with their monomers, korupensamines A (2a) and B (2b), were investigated using electrospray ionization tandem mass spectrometry coupled to liquid chromatography (LC-ESI-MS-MS). From the spectra obtained, characteristic product ions were chosen to monitor the chromatographic separation achieved on an RP-18 column. Under acidic conditions required for chromatographic analysis, the monomeric alkaloids 2a and 2b yielded protonated molecules [M + H]+, while the dimers, the michellamines, exhibited doubly protonated [M + 2H]2+ molecules. In addition, the coeluting alkaloids 1b and 2b were identified unambiguously be means of tandem mass spectrometry. Thus, together with the retention times of the alkaloids, the product ion spectra allowed us the identification of michellamines in the presence of their presumed biogenetic monomeric precursors. Application of the HPLC-MS-MS method successfully proved the enzymatic formation of michellamine C (1c) by in vitro dimerization of korupensamine B (2b).

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.