title: Stereochemical studies on algal pheromone biosynthesis. A model study with the flowering plant Senecio isatideus (Asteraceae).
abstract: Unsaturated C8 and C11 hydrocarbons act as chemical signals (chemotaxis) during sexual reproduction of many marine brown algae. One of these compounds, namely (+)-(6S)-6-(1Z-butenyl)cyclohepta-1,4-diene (= ectocarpene) is also formed as a major hydrocarbon by the flowering plant Senecio isatideus (Asteraceae). On administration of enantiospecifically labelled (8R)- or (8S)-[7,8-2H2]trideca-3,6,9-trienoic acid instead of the natural precursor dodeca-3,6,9-trienoic acid to this plant, the artificial C12 analogue of ectocarpene is formed. Mass spectroscopic analysis of the metabolites revealed this process to be enantiospecific for the C(8)-HRe atom of the precursor acid. The stereochemical course of the overall reaction is in agreement with a precise, U-shaped embedding of the trienoic acid into the active center of the enzyme(s) and Re-attack onto a hydrogen at the C(8) methylene group of this precursor. The reactive intermediate cyclizes by pi-orbital interaction between C(4) and C(6) of the acid and is accompanied by decarboxylation. The first product is a thermally unstable (1S,2R)-cis-1-(1E,3Z-hexadienyl)-2-vinylcyclopropane, which immediately rearranges to (+)-(6S)-ectocarpene (homo-Cope rearrangement). The present work provides first experimental evidence for a homo-Cope rearrangement as a naturally occurring electrocyclic reaction.
authors.affiliation: Institut für Organische Chemie der Universität, Karlsruhe, Federal Republic of Germany.
authors.forename: C
authors.initials: C
authors.lastname: Neumann
authors.forename: W
authors.initials: W
authors.lastname: Boland
mesh_terms: D003500:Cyclization; D003508:Cycloheptanes / Q000378:metabolism*; D056890:Eukaryota / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006358:Hot Temperature; D008958:Models, Molecular; D008968:Molecular Conformation; D000459:Phaeophyceae / Q000378:metabolism*; D010675:Pheromones / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*; D013237:Stereoisomerism
chemical_list: D003508:Cycloheptanes; D010675:Pheromones; C044377:ectocarpene