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Displaying results 1 to 10 of 12.

Publications

Thuy, T. T.; Ripperger, H.; Porzel, A.; Sung, T. V.; Adam, G.; Counlarins, limonoids and an alkaloid from Clausena excavata Phytochemistry 52, 511-516, (1999) DOI: 10.1016/S0031-9422(99)00122-3

In addition to a known alkaloid, some limonoids and coumarins, the new coumarins excavatins A–M have been isolated from Clausena excavata. Their structures have been assigned by NMR and CD investigations.
Publications

Thuy, T. T.; Porzel, A.; Ripperger, H.; Sung, T. V.; Adam, G.; Bishordeninyl terpene alkaloids from Zanthoxylum avicennae Phytochemistry 50, 903-907, (1999) DOI: 10.1016/S0031-9422(98)00612-8

In addition to (−)-culantraramine and (−)-culantraraminol the bishordeninyl terpene alkaloids, (−)-culantraramine N-oxide, (−)-culantraraminol N-oxide and avicennamine, have been isolated from the leaves of Zanthoxylum avicennae. Their structures have been assigned by MS and especially by NMR investigations.
Publications

Miersch, O.; Porzel, A.; Wasternack, C.; Microbial conversion of jasmonates - hydroxylations by Aspergillus niger Phytochemistry 50, 1147-1152, (1999) DOI: 10.1016/S0031-9422(98)00698-0

Aspergillus niger is able to hydroxylate the pentenyl side chain of (−)-jasmonic acid (JA) leading to (11S)- (−)-hydroxy-JA/ (11R)- (−)-hydroxy-JA (2:1) and (−)-11,12-didehydro-JA. Methyl (−)-jasmonate (JA-Me) is converted upon hydrolysis. During prolonged cultivation or at non-optimized isolation procedures, the 11-hydroxy- (9Z)-pentenyl side chain may isomerize to (10E)-9-hydroxy- and (9E)-11-hydroxy-compounds by allylic rearrangement. The fungus hydroxylates (±)-9,10-dihydro-JA at position C-11 into 11j-hydroxy-9,10-dihydro-JA. As JA-Me, the methyl dihydro-JA is hydroxylated only upon hydrolysis into the free acid.
Publications

Lichtblau, D.; Porzel, A.; Schmidt, J.; Voigt, B.; Adam, G.; Synthesis of a novel brassinosteroid type with an annelated dioxonane side chain J. Chem. Soc., Perkin Trans. 1 1999, 53-58, (1999) DOI: 10.1039/A807078D

In studies directed towards the synthesis of 25-hydroxybrassinolide 1 we found, that upon reaction of intermediate 7 with trimethylaluminium–n-butyllithium an alkylating fission of the epoxide ring and rearrangement of the tetrahydropyranyl unit takes place to afford after deprotection the new dioxonane-annelated brassinosteroid 9.
Publications

Kramell, R.; Porzel, A.; Miersch, O.; Schneider, G.; Wasternack, C.; Chromatographic resolution of peptide-like conjugates of jasmonic acid and of cucurbic acid isomers J. Chromatogr. A 847, 103-107, (1999) DOI: 10.1016/S0021-9673(99)00335-0

The chiral separation of peptide-like conjugates of jasmonic acid and of cucurbic acid isomers was investigated by liquid chromatography on Chiralpak AS and Nucleodex β-PM. The retention sequences reflect distinct chromatographic properties with respect to the chirality of the jasmonic acid part or of the cucurbic acid isomers. The chromatographic behaviour of the amide conjugates on a reversed-phase C18 column provides evidence for the resolution of diastereomeric conjugates depending on the chirality of both constituents of the conjugate molecule. The chromatographic procedures are suitable for the analytical and preparative separation of such conjugates.
Publications

Kramell, R.; Porzel, A.; Miersch, O.; Schneider, G.; Analysis of synthetic isoleucine conjugates of cucurbic acid isomers by liquid chromatography Phytochem. Anal. 10, 82-87, (1999) DOI: 10.1002/(SICI)1099-1565(199903/04)10:2<82::AID-PCA448>3.0.CO;2-K

Conjugates of 3,7‐trans cucurbic acid isomers with either (S )‐ or (R )‐isoleucine were synthesised from the diastereomeric conjugate of (3R , 7R )‐jasmonic acid and (3S , 7S )‐jasmonic acid by sodium borohydride reduction. The resulting diastereomers were characterised by nuclear magnetic resonance spectra. The authentic substances were subjected to liquid chromatography using a reversed‐phase C18 matrix and the chiral stationary phase Chiralpak AS. For all (6RS )‐hydroxy epimeric pairs, a baseline separation could be observed. The elution sequences obtained indicate that the 3,6‐trans oriented epimers with (S )‐isoleucine elute prior to the 3,6‐cis configured individuals independent of the mode of chromatography. In contrast, the elution pattern of the conjugates containing (R )‐isoleucine was reversed on the chiral stationary phase. The epimers with a 3,6‐cis configured hydroxy group and the acid side chain eluted faster than those with the 3,6‐trans configuration. The chromatographic conditions described are suitable for resolving mixtures of isomeric N‐(cucurbinoyl)‐isoleucines in order to assign their stereochemistry and to obtain chiral reference materials on a preparative scale.
Publications

Drosihn, S.; Porzel, A.; Voigt, B.; Brandt, W.; Wagner, C.; Merzweiler, K.; Adam, G.; Conformational studies of two new brassinosteroid analogues with a 22,23-trans diol function J. Chem. Soc., Perkin Trans. 2 1999, 233-238, (1999) DOI: 10.1039/A807440B

22,24-Diepiteasterone (3) and 23,24-diepiteasterone (4) were synthesized starting from a mixture of the corresponding (22S,23S)- and (22R,23R)-epoxides. Using detailed NOE investigations and molecular dynamic simulations with explicit solvent, the preferred conformations of both compounds were determined in solution. For both compounds 3 and 4 a preferred conformation of the side chain was found. For 4, by X-ray analysis the conformation in crystalline state was determined which differs distinctly from that in solution.
Publications

Buske, A.; Busemann, S.; Mühlbacher, J.; Schmidt, J.; Porzel, A.; Bringmann, G.; Adam, G.; Antidesmone, a novel type isoquinoline alkaloid from Antidesma membranaceum (Euphorbiaceae) Tetrahedron 55, 1079-1086, (1999) DOI: 10.1016/S0040-4020(98)01107-7

A novel type of tetrahydroisoquinoline alkaloid, antidesmone (1), was isolated from Antidesma membranaceum Müll. Arg.. The structure of 1 was determined to be (5S)-1-hydroxy-4-methoxy-3-methyl-5-octyl-5,6,7,8-tetrahydroisoquinolin-8-one by spectroscopic methods (MS, 1H, 13C 2D NMR, CD) and chemical derivatisation. The absolute (S)-configuration was determined by quantumchemical calculation of CD spectra.Antidesmone (1), a novel type of tetrahydroisoquinoline alkaloid, was isolated from Antidesma membranaceum Müll. Arg. The structure of 1 was determined to be (5S)-1-hydroxy-4-methyl-5-octyl-5,6,7,8-tetrahydroisoquinolin-8-one.
Publications

Ang'edu, C. A.; Schmidt, J.; Porzel, A.; Gitu, P.; Midiwo, J. O.; Adam, G.; Coumarins from Hypericum keniense (Guttiferae) Pharmazie 54, 235-236, (1999)

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Publications

Rothe, K.; Porzel, A.; Neumann, S.; Grimm, E.; Characteristics of the phloem path: analysis and distribution of carbohydrates in the petiole of Cyclamen J. Exp. Bot. 50, 1807-1816, (1999) DOI: 10.1093/jxb/50.341.1807

Compartmentation fluxes of carbohydrates along the phloem path were analysed in the petiole of Cyclamen persicum (L.) Mill. Sucrose represented the dominant fraction (58–75% of soluble carbohydrates in the vascular symplast). Planteose (12–22%), glucose (3–8%) and fructose (3–13%) occurred in lower amounts (data from liquid chromatography, percentages of the total peak area). Starch was not detectable. Upon feeding leaves with 14CO2, 98% and 90% of radiolabel was recovered as sucrose in the vascular symplast after 3 h and 24 h, respectively. Thus, sucrose appeared to be the exclusive transport sugar in Cyclamen. Experiments with asymmetrically labelled sucrose revealed that there was no metabolism of translocated sucrose. Analysis of six consecutive petiole segments (each 2 cm in length) showed a homogeneous longitudinal distribution of sucrose and planteose. The lateral distribution of these sugars differed markedly. On average, the sucrose concentration amounted to 4.7 and 0.4 mg g−1 FM in the vascular apoplast and petiole parenchyma, respectively. Sucrose was unloaded without hydrolysis and stored in the periphery of the phloem path. Planteose was identified as another storage saccharide. Sucrose synthesis by sucrose phosphate synthase occurred when isolated vascular bundles were incubated with [14C]glucose or [14C]fructose. These data suggest that the phloem path is characterized by both source and sink like activity.
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