Chemical markers in Veronica sect. Hebe. III☆

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Abstract

In a continued chemosystematic investigation of the water-soluble compounds in Veronica sect. Hebe, we have investigated two more of the species formerly classified as Parahebe. Both species contained mannitol in considerable amounts and in addition some glucosides of iridoid acids. Veronica cheesemanii was characterised by aucubin and its esters: 2′-O-benzoylaucubin and an aucubin diester named cheesemanioside. The main iridoid compounds in Veronica hookeriana were catalpol and its ester verminoside, but this species also contained the sugar ester methyl 1-O-benzoyl-3-α-glucuronosylglycerol and a caffeoyl phenylethanoid glycoside (CPG) named parahebeoside, a 2′-O-β-xylopyranosyl derivative of the known plantamajoside. The results show that the studied species of the former genus Parahebe are very different with regard to their chemical content. This is in agreement with the DNA sequence data and implies the genus was polyphyletic as previously circumscribed.

Introduction

In a number of studies of Veronica L. and its related genera (Albach and Chase, 2001, Albach and Chase, 2004) it has been demonstrated that the Southern Hemisphere genera Hebe Juss. and Parahebe W. Oliv. are derived from within Veronica. Consequently they have now been included in this genus in section Hebe (Albach et al., 2004, Garnock-Jones et al., 2007). The genera Veronica and Hebe have traditionally been considered members of the family Scrophulariaceae. However, Veronica (and thus Hebe) has recently been transferred to the Plantaginaceae (Albach et al., 2005, Olmstead, 2005).

The chemotaxonomic investigations of Veronica (Taskova et al., 2004, Taskova et al., 2006, Jensen et al., 2005 and references therein), have shown that the iridoid glucosides aucubin (6), catalpol (7) and a variety of 6-O-catalpol esters (e.g. 7a and 7b) are characteristic for this genus. These are also present in sect. Hebe; however, from this taxon with more than 100 species, only a few different 6-O-catalpol esters have so far been isolated, namely the 3,4-dihydroxybenzoyl ester verproside and/or verminoside (7b). Within section Hebe some species are also characterised by 6-O-rhamnopyranosyl-substituted iridoids, compounds not found in Northern Hemisphere representatives of the genus. Iridoids are usually accompanied by caffeoyl 3,4-dihydroxyphenylethanoid glycosides (CPGs). In a recent study of Veronica sect. Hebe (Jensen et al., 2008), we investigated Veronica catarractae G. Forster that was previously classified as Parahebe. The current paper reports our chemotaxonomic investigation of another two species formerly included in this taxon, Veronica cheesemanii Benth. and Veronica hookeriana Walp.

Section snippets

General

Fresh plant material was homogenized with MeOH (4 × weight) and filtered. The concentrated extracts were partitioned in Et2O–H2O, after which the aq. phase was taken to dryness and separated by prep. chromatography using a reverse phase Merck Lobar RP-18 SiGel column (size B) and H2O–MeOH mixtures (1:0–1:2) as the eluents. Difficult separations were done on a Merck HiBar column (250–25) packed with LiChrosorb RP-18 (7 μm). Isolated compounds are listed in order of elution; the proportion of

Results and discussion

Fresh foliage of V. cheesemanii and V. hookeriana was extracted with methanol and the water-soluble part of the extract was subjected to reverse phase column chromatography. In both species mannitol (1) was the main carbohydrate; they also contained the iridoid glucosides epiloganic acid (2), mussaenosidic acid (3) and arborescosidic acid (5). In addition to these common constituents, V. cheesemanii contained large amounts of aucubin (6), 2′-O-benzoylaucubin (6a) as well as a novel diester of

Acknowledgements

We thank Dr Philip Garnock-Jones, Victoria University of Wellington, New Zealand, for providing the authenticated plant material, and Kristian Fog Nielsen, BioCentrum, DTU, for recording the mass spectra.

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      2020, Saudi Pharmaceutical Journal
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      Our phytochemical studies on the aqueous extract prepared from the aerial parts of P. major subsp. major resulted in the isolation of three previously known compounds (Fig. 1). The chemical structures of these compounds were identified as calceorioside B (1), homoplantaginin (2) and plantamajoside (3) by comparing their spectroscopic data with the relevant literatures previously published (Zheng et al., 2002; Dawa et al., 2009; Maggi et al., 2009; Jensen et al., 2011). Despite the extract (27.04%), and among the isolated compounds, calceorioside B (41.16%) exerted significant inhibition at 100 μg/mL when compared to reference compound, homoplantaginin and plantamajoside were found to be inactive in the hyaluronidase enzyme inhibition test at the same concentration (Fig. 2).

    • Iridoid glucosides in the genus Veronica (Plantaginaceae) from New Zealand

      2017, Phytochemistry
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      Pseudoveronica using cultivated specimens of sect. Hebe (Johansen et al., 2007; Pedersen et al., 2007) and sect. Labiatoides (Jensen et al., 2008). This was followed by material collected in the wild in New Zealand (Maggi et al., 2009; Taskova et al., 2010, 2011; 2012). We have now investigated Veronica hookeri (Buchanan) Garn.-Jones (syn.

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      2015, Natural Product Research

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      2012, Phytochemistry
      Citation Excerpt :

      Although present in relatively small amounts, a variety of different esters were isolated and identified. As in other species of Veronica sect. Hebe the majority of CPGs were 2′-arabinosyl derivatives of plantamajoside (Pedersen et al., 2007; Jensen et al., 2008; Maggi et al., 2009; Taskova et al., 2010, 2011). The latter is a CPG with a 3′-O-glucosyl substituent typical and somewhat unique to the Plantaginaceae (Jensen et al., 2011).

    • A new phenylethanoid triglycoside in Veronica beccabunga L

      2011, Biochemical Systematics and Ecology
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    ☆

    The second paper in this series is Pedersen et al., 2007.

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