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Publications - Bioorganic Chemistry

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Publications

Winter, J.; Schneider, B.; Meyenburg, S.; Strack, D.; Adam, G.; Monitoring brassinosteroid biosynthetic enzymes by fluorescent tagging and HPLC analysis of their substrates and products Phytochemistry 51, 237-242, (1999) DOI: 10.1016/S0031-9422(98)00760-2

Both the vicinal side chain hydroxyl groups and the 6-oxo function of brassinosteroids were modified by fluorescence tagging. Dansylaminophenylboronic acid was used as a derivatizing agent to form fluorescent esters of brassinosteroids containing a side-chain cis-diol structure. 6-Oxo type brassinosteroids were derivatized by means of dansylhydrazine. The modified brassinosteroids, as far as possible derivatized both at the diol and the oxo group, were separated by HPLC and the optimal emission wavelength was determined. By this approach almost all brassinosteroids, including biosynthetic precursors, were susceptible to highly sensitive analysis in the fmol range. This method has been verified as an analytical tool to determine brassinosteroids in cell culture extracts and to monitor brassinosteroid biosynthetic enzymes. 24-Epibrassinolide has been detected in tomato cell suspension cultures. Several steps of brassinosteroid biosynthesis, including the Baeyer–Villiger oxidation of 24-epicastasterone to give 24-epibrassinolide, were monitored in vitro with protein preparations of the same cell culture line.
Publications

Wessjohann, L. A.; Scheid, G.; Recent Advances in Chromium(II)- and Chromium(III)-Mediated Organic Synthesis Synthesis 1999, 1-36, (1999) DOI: 10.1055/s-1999-3672

Synthetic transformations utilizing chromium(II) or chromium(III) reagents, mainly C-C-coupling reactions, are discussed. Chromium reagents find increasing application in complex total syntheses where other organometallics are difficult to apply. They are easy to prepare and exhibit extraordinary chemoselectivity and high diastereoselectivity. In this article emphasis is laid on recent results in synthetic procedures, on little known general aspects of (organo)chromium chemistry, and on areas not reviewed before. The most important recent advances include reactions catalytic in chromium ions, anti-selective Reformatsky-type aldol reactions with excellent asymmetric induction, domino radical/carbanion reactions, asymmetric chromium(III) catalyzed epoxide openings and homogeneous alkene polymerization catalysts. Some progress is also made in ligand controlled enantioselective reactions with Cr(II) reagents, but satisfying solutions remain a major challenge in the field.
Publications

Weiss, M.; Schmidt, J.; Neumann, D.; Wray, V.; Christ, R.; Strack, D.; Phenylpropanoids in mycorrhizas of the Pinaceae Planta 208, 491-502, (1999) DOI: 10.1007/s004250050586

Tissue-specific accumulation of phenylpropanoids was studied in mycorrhizas of the conifers, silver fir (Abies alba Mill.), Norway spruce [Picea abies (L.) Karst.], white pine (Pinus strobus L.), Scots pine (Pinus silvestris L.), and Douglas fir [Pseudotsuga menziesii (Mirbel) Franco], using high-performance liquid chromatography and histochemical methods. The compounds identified were soluble flavanols (catechin and epicatechin), proanthocyanidins (mainly dimeric catechins and/or epicatechins), stilbene glucosides (astringin and isorhapontin), one dihydroflavonol glucoside (taxifolin 3′-O-glucopyranoside), and a hydroxycinnamate derivative (unknown ferulate conjugate). In addition, a cell wall-bound hydroxycinnamate (ferulate) and a hydroxybenzaldehyde (vanillin) were analysed. Colonisation of the root by the fungal symbiont correlated with the distribution pattern of the above phenylpropanoids in mycorrhizas suggesting that these compounds play an essential role in restricting fungal growth. The levels of flavanols and cell wall-bound ferulate within the cortex were high in the apical part and decreased to the proximal side of the mycorrhizas. In both Douglas fir and silver fir, which allowed separation of inner and outer parts of the cortical tissues, a characteristic transversal distribution of these compounds was found: high levels in the inner non-colonised part of the cortex and low levels in the outer part where the Hartig net is formed. Restriction of fungal growth to the outer cortex may also be achieved by characteristic cell wall thickening of the inner cortex which exhibited flavanolic wall infusions in Douglas fir mycorrhizas. Long and short roots of conifers from natural stands showed similar distribution patterns of phenylpropanoids and cell wall thickening compared to the respective mycorrhizas. These results are discussed with respect to co-evolutionary adaptation of both symbiotic partners regarding root structure (anatomy) and root chemistry.
Publications

Vogt, T.; Ibdah, M.; Schmidt, J.; Wray, V.; Nimtz, M.; Strack, D.; Light-induced betacyanin and flavonol accumulation in bladder cells of Mesembryanthemum crystallinum Phytochemistry 52, 583-592, (1999) DOI: 10.1016/S0031-9422(99)00151-X

Treatment of the halophyte Mesembryanthemum crystallinum L. (ice plant) (Aizoaceae) with high intensities of white light resulted in a rapid cell-specific accumulation of betacyanins and flavonoids with 6-methoxyisorhamnetin 3-O-{[(2‴-E-feruloyl)-3‴-O-(β-d-glucopyranosyl)](2″-O-β-d-xylopyranosyl)}-β-d-glucopyranoside (mesembryanthin) as the predominant component, within bladder cells of the leaf epidermis. Induced accumulation of these metabolites was first detected 18 h after the initiation of light treatment in bladder cells located at the tip of young leaves followed by the bladder cells located on the epidermis of fully expanded leaves. UV-A light apparently is sufficient to induce accumulation of betacyanins and flavonoids. Application of 2-aminoindan 2-phosphonic acid, a specific inhibitor of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), not only inhibited the accumulation of flavonoids but also reduced betacyanin formation. Based on these observations we suggest these bladder cells as a model system to study regulation of betacyanin and flavonoid biosyntheses.
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

Siener, T.; Holzgrabe, U.; Drosihn, S.; Brandt, W.; Conformational and configurational behaviour of κ-agonistic 3,7-diazabicyclo[3.3.1]nonan-9-ones—synthesis, nuclear magnetic resonance studies and semiempirical PM3 calculations J. Chem. Soc., Perkin Trans. 2 1999, 1827-1834, (1999) DOI: 10.1039/A806641H

2,4-Diaryl substituted 3,7-diazabicyclo[3.3.1]nonan-9-one 1,5-diesters were found to have a high affinity for κ-opioid receptors. To develop highly potent analgesics, the purpose of this study was the synthesis and the structural characterisation of the novel 2,4-bis(4-nitrophenyl), 2,4-bis(3-nitrophenyl), 2,4-bis(4-quinolyl), 2,4-bis(2-quinolyl), 2,4-bis(1-naphthyl) and 2,4-bis(2-naphthyl) substituted 3,7-diazabicyclo[3.3.1]nonan-9-one 1,5-diesters by means of NMR spectroscopy and molecular modelling. It could be proved that several derivatives undergo trans–cis-isomerisation of the aromatic rings linked to the rigid skeleton whereas others show rotational isomerisation. Semiempirical quantum-chemical PM3 calculations were performed to analyse the thermodynamic stability of the isomers as well as the mechanism of the trans–cis- or cis–trans-conversion.
Publications

Schröder, G.; Unterbusch, E.; Kaltenbach, M.; Schmidt, J.; Strack, D.; De Luca, V.; Schröder, J.; Light-induced cytochrome P450-dependent enzyme in indole alkaloid biosynthesis: tabersonine 16-hydroxylase FEBS Lett. 458, 97-102, (1999) DOI: 10.1016/S0014-5793(99)01138-2

Vinblastine and vincristine are two medically important bisindole alkaloids from Catharanthus roseus (Madagascar periwinkle). Attempts at production in cell cultures failed because a part of the complex pathway was not active, i.e. from tabersonine to vindoline. It starts with tabersonine 16-hydroxylase (T16H), a cytochrome P450-dependent enzyme. We now show that T16H is induced in the suspension culture by light and we report the cloning of the cDNA. The enzyme was expressed in Escherichia coli as translational fusion with the P450 reductase from C. roseus, and the reaction product was identified by mass spectrometry. The protein (CYP71D12) shares 47–52% identity with other members of the CYP71D subfamily with unknown function. The induction by light was strongly enhanced by a nutritional downshift (transfer into 8% aqueous sucrose). We discuss the possibility that the entire pathway to bisindoles can be expressed in suspension cultures.
Publications

Schmidt, A.; Grimm, R.; Schmidt, J.; Scheel, D.; Strack, D.; Rosahl, S.; Cloning and Expression of a Potato cDNA Encoding Hydroxycinnamoyl-CoA:Tyramine N-(Hydroxycinnamoyl)transferase J. Biol. Chem. 274, 4273-4280, (1999) DOI: 10.1074/jbc.274.7.4273

Hydroxycinnamoyl-CoA:tyramineN-(hydroxycinnamoyl)transferase (THT; EC 2.3.1.110) catalyzes the transfer of hydroxycinnamic acids from the respective CoA esters to tyramine and other amines in the formation ofN-(hydroxycinnamoyl)amines. Expression of THT is induced byPhytophthora infestans, the causative agent of late blight disease in potato. The amino acid sequences of nine endopeptidase LysC-liberated peptides from purified potato THT were determined. Using degenerate primers, a THT-specific fragment was obtained by reverse transcription-polymerase chain reaction, and THT cDNA clones were isolated from a library constructed from RNA of elicitor-treated potato cells. The open reading frame encoding a protein of 248 amino acids was expressed in Escherichia coli. Recombinant THT exhibited a broad substrate specificity, similar to that of native potato THT, accepting cinnamoyl-, 4-coumaroyl-, caffeoyl-, feruloyl- and sinapoyl-CoA as acyl donors and tyramine, octopamine, and noradrenalin as acceptors tested. Elicitor-induced THT transcript accumulation in cultured potato cells peaked 5 h after initiation of treatment, whereas enzyme activity was highest from 5 to 30 h after elicitation. In soil-grown potato plants, THT mRNA was most abundant in roots. Genomic Southern analyses indicate that, in potato, THT is encoded by a multigene family.
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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