Biogenetic interrelationships of ergot alkaloids.
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A suitable method has been developed for the routine analysis of the ergot alkaloids ergometrine, ergometrinine, ergosine, ergosinine, ergotamine, ergotaminine, ergocornine, ergocorninine, alpha-ergocryptine, alpha-ergocryptinine, beta-ergocryptine, beta-ergocryptinine, ergocristine and ergocristinine in cereal products. The method consists of food extraction, cleaning of the crude extract by a modified form of the Extrelut method, and identification and quantitative determination of the alkaloids by high pressure liquid chromatography (HPLC). The results are confirmed by thin layer chromatography (TLC) and gas-chromatography/mass spectrometry (GC/MS). Market investigations have shown contaminations in ecological as well as in conventional products, with rye products mainly being contaminated. Within the EEC, a maximum value of 0.05% ergot respectively a total alkaloid content of 1 mg/kg in cereals used for food production is prescribed. This value was not exceeded in any of the investigated samples.
Many cool-season grasses harbor fungal endophytes in the genus Neotyphodium, which enhance host fitness, but some also produce metabolites--such as ergovaline--believed to cause livestock toxicoses. In Claviceps species the first step in ergot alkaloid biosynthesis is thought to be dimethylallyltryptophan (DMAT) synthase, encoded by dmaW, previously cloned from Claviceps fusiformis. Here we report the cloning and characterization of dmaW from Neotyphodium sp. isolate Lp1, an endophyte of perennial ryegrass (Lolium perenne). The gene was then disrupted, and the mutant failed to produce any detectable ergovaline or simpler ergot and clavine alkaloids. The disruption was complemented with the C. fusiformis gene, which restored ergovaline production. Thus, the biosynthetic role of DMAT synthase was confirmed, and a mutant was generated for future studies of the ecological and agricultural importance of ergot alkaloids in endophytes of grasses.
Natural sources, i.e. fungal strains and species producing ergot alkaloids (EA), are surveyed together with the chemical structures of EA and a list of new natural EA discovered in the last three decades. Other topics include new efficient chromatographic methods (HPLC) for the separation and isolation of new natural EA and also immunological methods of EA detection.
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The present paper investigated the proliferative response of murine splenic cells in the tissue culture after stimulation with the polyclonal activators PHA, ConA and PWM. Proliferation of cells and DNA synthesis were measured by means of radioactively labelled thymidine. Furthermore, the primary antibody response of murine splenic cells in the tissue culture after activation with sheep red blood cells was examined. The response was measured by determining the number of plaque forming cells (PFC). The number of PFC's was determined by the plaque method of local haemolysis, in modification by the drop method. In these tests the ergot alkaloids dihydroergocornine, dihydroergocristine, dihydro-alpha-ergocryptine and dihydro-beta-ergocryptine were evaluated in two doses, 600 and 1200 micrograms/kg/day p. o. for the period of 14 days. Dihydroergocornine in these tests increased the primary antibody response in a statistically significant manner; on the other hand, after its administration in the higher dose decreased proliferation after PHA was found. The finding after dihydroergocristine administration was of interest. This ergot alkaloid slightly increased proliferation of cells after PHA and PWM as well as the primary antibody response of murine cells. After the administration of dihydro-alpha-ergocryptine increased proliferation after stimulation with PWM and increased primary antibody response, and after the administration of dihydro-beta-ergocryptine increased proliferation of cells after stimulation with PHA were found.
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Using the chiral methyl group methodology, the methylation step in the biosynthesis of ergot alkaloids catalyzed by the enzyme AdoMet:dimethylallyltryptophan N-methyltransferase was found to proceed with net inversion of methyl group configuration. The enzyme thus conforms to the majority of methyltransferases studied which mediate a direct SN2 transfer of the methyl group from AdoMet to the acceptor nucleophile in a ternary enzyme substrate complex.
Two novel natural derivatives (2 and 3) of the ergot alkaloid alpha-ergokryptine (1), as well as their synthetically brominated analogues (5 and 6) were isolated and identified by NMR and MS methods. Compounds 2 and 5 contain what appears to be a so far unknown natural amino acid building block. Complete 1H and 13C NMR assignments are given for compounds 1-6.
Pharmacokinetic studies were carried out with nine tritium-labeled ergot alkaloids (dihydroergotmine, dihydroergotoxine, dihydroergostine, dihydroergocornine, dihydroergovaline, dihydroergonine, ergotamine, 1-methyl-ergotamine, and bromocriptine). Each drug was administered to 6 subjects in a randomized cross-over design as single oral and intravenous doses. Plasma levels and urinary excretion of tritium-labeled material were analyzed on a phenomenological basis by non-linear regression as a sum of exponentials. All substances showed the highest plasma concentration about 2 hours after oral administration (range 1.0-2.7 hours). The mean invasion half-life was 0.5 hours (range 0.32-1.12 hours). The mean elimination half-lives ranged from 1.4-6.2 hours for the alpha-phase and from 13 to 50 hours for the beta-phase, the longest values being observed with bromocriptine. From cumulative urinary excretion data after oral and after intravenous administration, a quotient of absorption was calculated. Values between 25 and 30% were found for most dihydrogenated drugs, namely dihydroergotamine, dihydroergotoxine, dihydroergostine, and dihydroergocornine, the only exceptions being dihydroergovaline and dihydroergonine, which were less well absorbed. Ergotamine and 1-methyl-ergotamine had an absorption quotient of about two-thirds and bromocriptine was nearly completely absorbed.
High concentration of inorganic phosphate in the culture medium of Aspergillus fumigatus inhibited ergot alkaloid synthesis. Addition of L-tryptophan but not mevalonate or 5-methyltryptophan to the above culture restored the alkaloid synthesis to the level found in normal cultures. The decrease in alkaloid synthesis in the fungus accompanies an increase in cell mass, cellular protein and sterol content. Aspartate aminotransferase and alanine aminotransferase activities were significantly increased in the high-phosphate culture.
A method is described for the isolation, separation and quantitative determination of ergot alkaloids in cereals and cereal products.