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Biosynthesis of ergot alkaloids. Evidence for two isomerizations in the isoprenoid moiety during the formation of tetracyclic ergolines

Journal of the American Chemical Society (Impact Factor: 11.44). 12/1968; 90(23):6500-7. DOI: 10.1021/ja01025a048
Source: PubMed

ABSTRACT Canoclavine-I (1), but not chanoclavine-II (5) or isochanoclavine-I (6), is an efficient precursor of tetracyclic ergot alkaloids. Its cyclization to give agroclavine (2) is accompanied by a cis-trans isomerization at the double bond of the isoprenoid moiety. Experiments with mevalonic acids stereospecifically tritiated at C-4 indicate that another such cis-trans isomerization occurs earlier in the pathway. Thus the apparently "normal" labeling of tetracyclic ergot alkaloids from mevalonic-2-14C acid in the trans-carbon atom of the isoprenoid moiety is an accidental result caused by two isomerizations. The cyclization of chanoclavine-I proceeds with complete retention of the hydrogen at C-10, but with only 70% retention of the hydrogen at C-9. The latter result is discussed in view of possible mechanisms of the reaction.

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    • "This inversion occurs in a later step and it is of mechanistic importance as it is under full retention of hydrogen. Later, in agreement with these findings, DMAT (17) was detected as free intermediate in Claviceps mycelium when total synthesis of alkaloids was inhibited by depriving Claviceps cultures from supply with oxygen or adding ethionine that finally established a direct correlation between DMAT formation and alkaloid synthesis (Robber and Floss, 1968; Agurell and Lindgren, 1968). "
    Ergot - The Genus Claviceps, Edited by V. Kren, L. Cvak, 01/1999: pages 95 - 163; Harwood Academic Publishers London.
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