Chemotaxonomy of Plantago. Iridoid glucosides and caeoyl phenylethanoid glycosides Nina Rùnsted a , Edith GoÈbel a,1 , Henrik Franzyk a , Sùren Rosendal Jensen a, *, Carl Erik Olsen b a Department of Organic Chemistry, The Technical University of Denmark, DK-2800 Lyngby, Denmark b Department of Chemistry, The Royal Veterinary and Agricultural University, DK-1871 Frederiksberg C, Denmark Received 2 May 2000; received in revised form 10 July 2000 Abstract Data for 34 species of Plantago (Plantaginaceae), including subgen. Littorella (=Littorella uni¯ora), have been collected with regard to their content of iridoid glucosides and caeoyl phenylethanoid glycosides (CPGs). In the present work, 21 species were investigated for the ®rst time and many known compounds were found together with three new iridoid glucosides. Of these, arborescoside and arborescosidic acid, both of the uncommon type with an 8,9-double bond, were present in several species, while 6-deoxymelittoside was found only in P. subulata. The known compounds deoxyloganic acid, caryoptoside and rehmannioside D were isolated from the genus for the ®rst time. The earlier reported occurrence of sorbitol in the family was con®rmed, and this compound was shown by NMR spectroscopy to be the main sugar in the three species investigated for this. The combined data show that CPGs are present in all species investigated. With regard to the iridoids, the distribution patterns showed a good correlation with the classi®cation of Rahn. Thus, aucubin is typical for the whole genus, while bartsioside and catalpol as well as 5-substituted iridoids are each characteristic for a subgenus in the family. Finally, the close relationship between Plantago and Veronica suggested by chloroplast DNA sequence analysis, could be corroborated by the common occurrence of the rare 8,9-unsaturated iridoids in these two genera. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Plantago; Plantaginaceae; Chemotaxonomy; Iridoid glucosides; Bartsioside; Aucubin; Catalpol; Arborescoside; Arborescosidic Acid; 6- Deoxymelittoside; Verbascoside; Sorbitol 1. Introduction In recent years, a considerable number of dierent iridoids have been isolated from the genus Plantago, and these include aucubin and compounds biosyntheti- cally related to it. The early work on the genus concerns mainly aucubin and catalpol and has been reviewed by Hegnauer (1969). A number of taxonomic works pri- marily by Swiatek (1977) and by Andrzejewska-Golec (1997), Andrzejewska-Golec and Swiatek (1984) and Andrzejewska-Golec et al. (1993) have shown that the iridoids can be used as valuable taxonomic markers. In addition, caeoyl phenylethanoid glycosides (CPGs) have been shown to be widely distributed in the genus and have similarly been suggested to be taxonomic markers (Andary et al., 1988) in the Plantaginaceae. As part of an ongoing study of the water-soluble com- pounds in the genus Plantago (Damtoft et al., 1994a; Jensen et al., 1996; Franzyk et al., 1998), we have now investigated a larger number of species for iridoids and CPGs. Previously, we have elucidated the biosynthesis of aucubin and catalpol, mainly in Scrophularia (Jensen, 1991, 1992; Damtoft et al., 1993, 1994b; Damtoft, 1994), but also more recently in Plantago major (Jensen et al., unpublished) to be that shown in Fig. 1. 2. Results In the present work, frozen plant material was homo- genized with ethanol and the water-soluble part was subjected to reverse phase chromatography. The fractions were monitored by NMR spectroscopy and the isolated compounds identi®ed by comparison with known data. Structures of new compounds were elucidated by spec- troscopy. In the following, we will go through the species 0031-9422/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0031-9422(00)00306-X Phytochemistry 55 (2000) 337±348 www.elsevier.com/locate/phytochem * Corresponding author. Tel.: +45-452-52103; fax: 45-459 33968. E-mail address: oksrj@pop.dtu.dk (S.R. Jensen). 1 Nee Falkesgaard.