Chemotaxonomy of the Oleaceae: Iridoids As Taxonomic Markers
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Phytochemistry 60 (2002) 213–231 www.elsevier.com/locate/phytochem Review Chemotaxonomy of the Oleaceae: iridoids as taxonomic markers Søren Rosendal Jensena,*, Henrik Franzyka, Eva Wallanderb aDepartment of Chemistry, The Technical University of Denmark, DK-2800, Lyngby, Denmark bBotanical Institute, Go¨teborg University, PO Box 461, SE-40530 Go¨teborg, Sweden Received 19 December 2001; received in revised form 6 March 2002 Abstract The distribution and biosynthesis of iridoid glucosides in the Oleaceae is reviewed and five distinct biosynthetic pathways to iri- doids have been identified in the family, deoxyloganic acid apparently being a common intermediate. Likewise, the distributions of caffeoyl phenylethanoid glycosides (CPGs), i.e. verbascoside and its analogues, as well as cornoside are listed. Iridoid glucoside data exist for 17 genera of Oleaceae and the occurrence of iridoids from the different biosynthetic pathways correlate extremely well with the phylogenetic classification inferred from recent chloroplast DNA sequence data. Thus the tribe Fontanesieae (Fontanesia)contains ‘‘normal’’ secoiridoids, Forsythieae (Abeliophyllum, Forsythia) contains cornoside and/or iridoids from the forsythide pathway, Myxopyreae (Myxopyrum, Nyctanthes) have iridoids from the myxopyroside pathway, and finally, the two tribes Jasmineae and Oleeae (the remaining genera) both contain iridoids from the oleoside pathway. Within Jasmineae, one group of Jasminum sp. is characterized by the presence of jasminin or similar compounds, while another group of Jasminum species and Menodora display derivatives of 10-hydroxyoleoside, compounds not present in the other group. CPGs are reported from about half of the species investigated. With regard to taxonomy at the order level, the chemical data might support a position within or close to Lamiales due to the common presence of CPGs, the iridoids being of less significance since they are of a type that are barely found elsewhere. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Oleaceae; Taxonomy; Phylogeny; Iridoid glucosides; Biosynthesis; Verbascoside; Cornoside; Menodora; Forestiera; Nestegis Contents 1. Introduction ............................................................................................................................................................................... 214 2. Biosynthesis of iridoids ..............................................................................................................................................................214 3. Iridoids and CPGs in Oleaceae ..................................................................................................................................................216 3.1. Abeliophyllum ....................................................................................................................................................................216 3.2. Forsythia............................................................................................................................................................................216 3.3. Nyctanthes ......................................................................................................................................................................... 218 3.4. Myxopyrum .......................................................................................................................................................................218 3.5. Fontanesia..........................................................................................................................................................................218 3.6. Menodora...........................................................................................................................................................................218 3.7. Jasminum ...........................................................................................................................................................................218 3.8. Syringa............................................................................................................................................................................... 220 3.9. Ligustrum...........................................................................................................................................................................221 3.10. Fraxinus............................................................................................................................................................................. 222 3.11. Chionanthus .......................................................................................................................................................................222 3.12. Forestiera...........................................................................................................................................................................223 3.13. Olea ................................................................................................................................................................................... 223 * Corresponding author. Tel.: +45-4525-2157/03; fax: +45-4593-3968. E-mail address: [email protected] (S.R. Jensen). 0031-9422/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0031-9422(02)00102-4 214 S.R. Jensen et al. / Phytochemistry 60 (2002) 213–231 3.14. Nestegis.............................................................................................................................................................................. 223 3.15. Phillyrea............................................................................................................................................................................. 224 3.16. Picconia ............................................................................................................................................................................. 224 3.17. Osmanthus ......................................................................................................................................................................... 224 4. Discussion .................................................................................................................................................................................. 224 5. Experimental .............................................................................................................................................................................. 227 5.1. Menodora robusta (Benth. A) Grey ...................................................................................................................................227 5.2. Forestiera acuminata (Michx.) Poir. ..................................................................................................................................227 5.3. Nestegis sandwicensis (Gray) O. & I. Deg. & L. Johnson..................................................................................................227 Acknowledgements..........................................................................................................................................................................227 References ....................................................................................................................................................................................... 227 1. Introduction when hydrolyzed by the enzymes in the plant (Konno et al., 1998, 1999). Thus, the glucoside is compartmenta- The Oleaceae is a family of medium size with 25 genera lized in the cells of the intact plant, but when the tissue and about 600 species. With regard to chemical con- is damaged by insect chewing, the compound is hydro- stituents, it has been quite extensively investigated. It is lyzed to the aglucone which react irreversibly with the mainly characterized by the presence of iridoid gluco- proteins and renders these more or less indigestible and sides and phenylethanoid derivatives in the form of thus useless, especially with regard to the essential esters and glycosides of tyrosol (p-hydroxyphenyl-etha- amino acid lysine. nol) and in particular the closely related dopaol (3,4- dihydroxyphenyl-ethanol). Coumarins and lignan glu- cosides are also common in the family, but they appear 2. Biosynthesis of iridoids to have a more limited distribution (Hegnauer, 1969, 1990). The presence of iridoids is linking Oleaceae both The iridoids are of terpenoid origin and their biosynth- to Lamiales and to Gentianales, and since most of the esis has been fairly well investigated (Inouye and Uesato, iridoids are formally of the seco-type, a closer relation- 1986; Jensen, 1991, 1992), thus it is known that two main ship with Gentianales is indicated. This fact was among routes exist. One main route (route I;Fig.1)isleading others adopted by Dahlgren (Dahlgren et al., 1981; from iridodial (1) via iridotrial (2) to deoxyloganic acid (3) Dahlgren, 1989) to place Oleales as a sister group to which is the known precursor of many carbocyclic iridoids Gentianales. However, the presence of tyrosol/dopaol- having the 8b-stereochemistry including loganin (6)and derivatives in Oleaceae, both as iridoid esters and loganic acid (10), secologanin and secologanic acid (11) (mainly) as verbascoside and its analogues (caffeoyl as well as the derived secoiridoids and complex indole phenylethanoid glycosides=CPGs) could conversely