title: Photochemical formation of intricarene.
abstract: Sunlight is the ultimate driver of biosynthesis but photochemical steps late in biosynthetic pathways are very rare. They appear to play a role in the formation of certain furanocembranoids isolated from Caribbean corals. One of these compounds, intricarene, has been suspected to arise from an intramolecular 1,3-dipolar cycloaddition involving an oxidopyrylium. Here we show, by a combination of experiments and theory, that the oxidopyrylium forms under photochemical conditions and that its cycloaddition occurs via a triplet state. The formation of a complex by-product can be rationalized by another photochemical step that involves a conical intersection. Our work raises the question whether intricarene is biosynthesized in the natural habitat of the corals or is an artefact formed during workup. It also demonstrates that the determination of exact irradiation spectra, in combination with quantum chemical calculations, enables the rationalization of complex reaction pathways that involve multiple excited states.
authors.affiliation: 1] Department of Chemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany [2] Center for Integrated Protein Science, 81377 Munich, Germany [3].
authors.forename: Desiree
authors.initials: D
authors.lastname: Stichnoth
authors.affiliation: 1] Department of Chemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany [2].
authors.forename: Patrick
authors.initials: P
authors.lastname: Kölle
authors.affiliation: 1] Department of Chemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany [2] Center for Integrated Protein Science, 81377 Munich, Germany.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Kimbrough
authors.affiliation: Faculty of Physics, Lehrstuhl für BioMolekulare Optik, Ludwig-Maximilians-Universität, 80538 Munich, Germany.
authors.forename: Eberhard
authors.initials: E
authors.lastname: Riedle
authors.affiliation: Department of Chemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany.
authors.forename: Regina
authors.initials: R
authors.lastname: de Vivie-Riedle
authors.affiliation: 1] Department of Chemistry, Ludwig-Maximilians-Universität, 81377 Munich, Germany [2] Center for Integrated Protein Science, 81377 Munich, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Trauner
mesh_terms: D000818:Animals; D037421:Anthozoa; D010788:Photosynthesis; D014315:Triterpenes / Q000378:metabolism*
chemical_list: D014315:Triterpenes; C507581:intricarene