OPTIMIZATION OF THE BIOTRANSFORMATION OF L-TYROSINE INTO L-DIHYDROXYPHENYLALANINE (DOPA) BY ALGINATE-ENTRAPPED CELLS OF MUCUNA-PRURIENS

The optimization of the biotransformation of l-tyrosine into l-dihydroxyphenylalanine (DOPA), and of formyl-tyrosine into formyl-DOPA by alginate-entrapped cells of Mucuna pruriens is reported. This optimization is discussed in terms of parameters that are relevant for the entrapped cell system (charge of the beads with cells, bead diameter, permeation of the cells) and some parameters that are relevant for the enzymatic transformation (pH, pO2, concentration of ascorbate). The optimization experiments resulted in the description of a biotransformation system which operates at a constant redox potential. With this transformation system a transformation efficiency of 70% could be obtained, at a biotransformation-rate of 435 μmol·h-1·g-1 (DW of cells) at a substrate concentration of 19 mM

PYRROLIZIDINE ALKALOIDS, FLAVONOIDS AND VOLATILE COMPOUNDS IN THE GENUS EUPATORIUM - EUPATORIUM-CANNABINUM L, AN ANCIENT DRUG WITH NEW PERSPECTIVES

Within the scope of a study of antitumour compounds in higher plants a survey is given concerning the presence of pyrrolizidine alkaloids, flavonoids and volatile compounds in Eupatorium species. Preliminary results of a phytochemical study of these compounds in E. cannabinum are also presented. From the results of a GC-MS analysis of an alkaloid extract from aerial parts of E. cannabinum the conclusion can be drawn, that the composition of pyrrolizidine alkaloids is more complicated than reported in literature. This is caused by the fact that different stereoisomers exist. The presence of at least two alkaloids with a molecular weight of 283 (supinine or isomers) and four alkaloids with a molecular weight of 299 (echinatine or isomers) could be shown. In subterranean plant material also other pyrrolizidine alkaloids are present. A great number of flavonoids, also as glycosides, have been shown in Eupatorium species, often in low quantities. Rutin, present in many Eupatorium species, could not be detected in subterranean parts of E. cannabinum. Relatively little attention has been paid to the analysis of volatile compounds (essential oils) of Eupatorium species. Thymol derivatives are often reported to be present in Eupatorium species. Thirty-five compounds could be detected by means of a GC-MS analysis in the essential oil of E. cannabinum about which no literature data were available

ON THE IMPROVEMENT OF THE PODOPHYLLOTOXIN PRODUCTION BY PHENYLPROPANOID PRECURSOR FEEDING TO CELL-CULTURES OF PODOPHYLLUM-HEXANDRUM ROYLE

In order to improve the production of the cytotoxic lignan podophyllotoxin, seven precursors from the phenylpropanoid-routing and one related compound were fed to cell suspension cultures derived from the rhizomes of Podophyllum hexandrum Royle. These cell cultures were able to convert only coniferin into podophyllotoxin, maximally a 12.8 fold increase in content was found. Permeabilization using isopropanol, in combination with coniferin as a substrate, did not result in an extra increase in podophyllotoxin accumulation. Concentrations of isopropanol exceeding 0.5% (v/v) were found to be rather toxic for suspension growth cells of P. hexandrum. When coniferin was fed in presence of such isopropanol concentrations, beta-glucosidase activity was still present, resulting in the formation of the aglucon coniferyl alcohol. In addition, podophyllotoxin was released into the medium under these permeabilization conditions. Entrapment of P. hexandrum cells in calcium-alginate as such or in combination with the feeding of biosynthetic precursors, did not improve the podophyllotoxin production. Cell-free medium from suspension cultures at later growth stages incubated with coniferin, resulted in the synthesis of the lignan pinoresinol