Preparation of eumelanin-related metabolites 5,6-dihydroxyindole, 5,6-dihydroxyindole-2-carboxylic acid, and their O-methyl derivatives

5,6-Dihydroxyindole (5,6DHI) and 5,6-dihydroxyindole-2-carboxylic acid (5,6DHI2C) are ultimate precursors of the black melanin, eumelanin. These indolic metabolites and their O-methyl derivatives are excreted in urine of melanoma patients at high levels and of healthy persons at low levels. We describe here a simplified procedure for preparing milligram to subgram quantities of 5,6DHI and 5,6DHI2C and their O-methyl derivatives. Dopachrome generated in situ by ferricyanide oxidation of dopa at pH 6.5 underwent spontaneous decarboxylation to give 5,6DHI in 40% isolation yield, while treatment of dopachrome with alkali at pH 13 afforded 5,6DHI2C in 38% isolation yield. Two isomeric O-methyl derivatives of 5,6DHI were prepared by treatment with diazomethane, while those of 5,6DHI2C were prepared by treatment with diazomethane followed by alkaline hydrolysis of the methyl esters. 5,6DHI and 6-hydroxy-5-methoxyindole were also obtained by heating the corresponding carboxylic acids in decalin. 5-Hydroxy-6-methoxyindole and 6-hydroxy-5-methoxyindole-2-carboxylic acid could also be prepared by debenzylation of the commercially available O-benzyl derivatives.     

Vegetation fluctuation in mediterranean dune ponds in relation to rainfall variation and water extraction

Abstract. The structure of dune ponds hygrophytic vegetation has a spatial organisation in belts around the pond basin, closely related to water level and flooding regime. Doñana National Park has an important representation of temporal dune ponds, which are subjected to rainfall fluctuations and may be suffering the impact of water extraction from the neighbouring tourist resort. Permanent transects in a vegetation complex of five dune ponds have been monitored during a eight year period (1990-1997). This period was characterised by a number of dry years (annual rainfall around 300 mm), located between two wet cycles (800-900 mm). Transects were analysed in 1990 (wet period), 1994 (dry) and 1997 (wet) by hierarchical agglomera-tive clustering. During the dry period hygrophytic species showed regression, with a high mortality of some species like Ulex minor, while the xerophytic species advanced to lower areas. Seedlings of some xerophytic species colonised the dry surface of the pond basin. The lowering of the water table varied in the different ponds, ranging from 312 to 190 cm depending on topography and the distance to the pumping area. The new period of flooding during 1995-96 and 1996-97 cycles provided the opportunity for hygrophytic spe cies to re-establish themselves in their original places. This study suggest that changes in vegetation are caused by the interaction between weather conditions and human disturbance (water extractions). In our example man-made disturbance is more marked during the dry periods while wet periods tend to obscure the effects of water extractions. From a management perspective, long-term monitoring of water table and vegetation structure is revealed as a key procedure to the management of land-water ecotones on pressured areas and threatened habitats.     

Expression of a lipocalin in prokaryote and eukaryote cells: quantification and structural characterization of recombinant bovine beta-lactoglobulin.

In this paper we quantify and characterize the expression of recombinant beta-lactoglobulin (rBLG) in prokaryote and eukaryote cells. In Escherichia coli we used the pET26 vector, which permits the secretion of rBLG in periplasm. We studied the expression of rBLG in COS-7 cells and in vivo in mouse tibialis muscle. The expression of rBLG was measured by two immunoassays specific, respectively, for BLG in its native and denatured conformation. We observed that rBLG was essentially expressed in a denatured form in E. coli even in the periplasm, whereas rBLG in eukaryote cells was found in its native conformation.     

Im-trityl protection of histidine.

A rational attempt to prepare FmocHis(piTrt)OH regiospecifically gave in fact the well-known tau-trityl isomer, and experiments with model systems indicate that the prospects for access to pi-trityl histidine derivatives, which would be of great value for the racemization-free synthesis of histidine-containing peptides, are poor.     

Inhibition of farnesylation blocks growth but not differentiation in FRTL-5 thyroid cells.

The cholesterol lowering drug lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, blocks DNA synthesis and proliferation of thyrotropin (TSH) primed FRTL-5 rat thyroid cells. The blockade can be completely prevented and/or reversed by mevalonate and largely prevented and/or reversed by farnesol whereas cholesterol and/or other non-sterol mevalonate derivatives such as ubiquinone, dolichol or isopentenyladenosine are ineffective. TSH-dependent augmentation of cyclic-AMP and cAMP dependent differentiated functions, such as iodide uptake, are unaffected by lovastatin. 3H-Thymidine incorporation into DNA is also decreased by alpha-hydroxyfarnesyl-phosphonic acid, an inhibitor of protein farnesylation which mimicks the effect of lovastatin since it also leaves unaffected TSH stimulated iodide uptake. It is suggested that the HMG-CoA reductase inhibitor lovastatin affects cell proliferation mainly through inhibition of protein farnesylation which results in altered function proteins relevant for proliferation control, notably p21ras and/or other small GTPases.     

Pharmakogenetik der oralen Antikoagulation mit Cumarinen

The recent identification of VKORC1 has made important contributions to our understanding of the vitamin K cycle. The VKORC1 enzyme was shown to be the molecular target of coumarin drugs. Mutations and polymorphisms in coding and noncoding regions of the VKORC1 gene have been shown to cause both a partial to total coumarin resistance and coumarin sensitivity. Availability of molecular diagnostics (VKORC1, CYP2C9) and drug monitoring by HCPLC (determination of coumarin, vitamin K, and vitamin K epoxide levels) is helpful for detecting hereditary and acquired factors influencing coumarin therapy. In the future, these tools may be instrumental in designing individualized oral anticoagulation therapy regimens.     

Transposition-mediated transcriptional overexpression as a mechanism of insecticide resistance

It has been proposed that amplification of genes for esterase that provide resistance to insecticides may originate from transposition events. To test this hypothesis, we have constructed a minigene coding for a soluble acetylcholinesterase under the control of a nontissue-specific promoter (hsp70). When introduced into Drosophila, the gene is expressed in all tissues and the extra acetylcholinesterase produced confers a low level of insecticide resistance (twofold). The minigene was mobilized by crossing the initial transformant with a strain providing a source of P-element transposase. After 34 generations of exposure to the organophosphate parathion, we obtained a strain with a higher resistance (fivefold). This strain had only one extra Ace gene, which overexpressed acetylcholinesterase. Thus, following transposition, resistance resulted from the overexpression of a single copy of the gene and not from gene amplification. Received: 9 August 1996 / Accepted: 27 May 1997