title: Structural revision of some recently published iridoid glucosides.
abstract: The structures of six different iridoid glucosides have been revised. Three compounds isolated from Eremostachys glabra and designated 6,9-epi-8-O-acetylshanziside (1), 5,9-epi-penstemoside (2), and 5,9-epi-7,8-didehydropenstemoside (3) have been shown to be identical to the known iridoids barlerin (4, 8-O-acetylshanziside), penstemoside (5), and 7,8-didehydropenstemoside (6), respectively. Another compound named harpagoside-B, isolated from Scrophularia deserti and proposed to be 9-epi-6-O-methylharpagoside (11), was demonstrated from the spectroscopic data given to be the known harpagoside (10b). Finally, two alleged iridoid galactosides from Buddleja crispa named buddlejosides A and B (12a and 12b) have been shown to be the corresponding glucosides; the former is identical to agnuside (13a), while the latter is 3,4-dihydroxybenzoylaucubin (13b), an iridoid glucoside not previously published. This clearly showed that care should be taken with the interpretation of NOEs involving bridgehead protons in iridoid structures because they can be capricious and lead to erroneous structural assignments.
authors.affiliation: Department of Chemistry, Technical University of Denmark, DK-2800, Lyngby, Denmark. srj@kemi.dtu.dk
authors.forename: Søren R
authors.initials: SR
authors.lastname: Jensen
authors.forename: Ihsan
authors.initials: I
authors.lastname: Caliş
authors.forename: Charlotte H
authors.initials: CH
authors.lastname: Gotfredsen
authors.forename: Inger
authors.initials: I
authors.lastname: Søtofte
mesh_terms: D032861:Buddleja / Q000737:chemistry; D039823:Iridoids / Q000737:chemistry*; D019686:Lamiaceae / Q000737:chemistry; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010946:Plants, Medicinal / Q000737:chemistry*; D032266:Scrophularia / Q000737:chemistry
chemical_list: D039823:Iridoids