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DOI: 10.1055/s-0043-108910
An Intramolecular CAr–H•••O=C Hydrogen Bond and the Configuration of Rotenoids[*]
Publication History
received 08 February 2017
revised 26 March 2017
accepted 04 April 2017
Publication Date:
20 April 2017 (online)
Abstract
Over the past half a century, the structure and configuration of the rotenoids, a group of natural products showing multiple promising bioactivities, have been established by interpretation of their NMR and electronic circular dichroism spectra and confirmed by analysis of single-crystal X-ray diffraction data. The chemical shift of the H-6′ 1H NMR resonance has been found to be an indicator of either a cis or trans C/D ring system. In the present study, four structures representing the central rings of a cis-, a trans-, a dehydro-, and an oxadehydro-rotenoid have been plotted using the Mercury program based on X-ray crystal structures reported previously, with the conformations of the C/D ring system, the local bond lengths or interatomic distances, hydrogen bond angles, and the H-6′ chemical shift of these compounds presented. It is shown for the first time that a trans-fused C/D ring system of rotenoids is preferred for the formation of a potential intramolecular C6′–H6′•••O=C4 H-bond, and that such H-bonding results in the 1H NMR resonance for H-6′ being shifted downfield.
Key words
Millettia caerulea - Fabaceae - rotenoids - intramolecular CAr–H•••O=C H-bond - NMR spectra and electronic effects - conformation and configuration* Dedicated to Professor Dr. Max Wichtl in recognition of his outstanding contributions to natural product research.
Supporting Information
- Supporting Information
Structures of rotenone, deguelin, and tephrosin and synthesis of deguelin, synthesis of [11-3H]-7-demethylmunduserone from 7,2′-di-hydroxy-4′,5′-di-methoxyisoflavone, chemical and crystal structures and ECD spectrum of (−)-rotenone, structures of (+)-3-hydroxy-α-toxicarol and (−)-caeruleanone D and their ECD spectra, structures and molecular models of (−)-rotenone, (−)-deguelin, (−)-tephrosin, (2R,3R,1″R,2″S)-1″,2″-dihydro-1″,2″-dihydroxytephrosin, and (+)-usararotenoid A, and their epimers, structures and molecular models of (−)-13-homo-13-oxa-2,3-dehydrorotenone and 2,3-dehydrosermundone and structures and selected δ values for several cis-rotenoids and their trans isomers are available as Supporting Information.
