Alkaloids

Early reports suggested the presence of alkaloids in Echinacea species but several subsequent workers were unable to verify this. The common plant

Formula Chart No. 6 Unsaturated alkyl amides of echinacea.

Formula Chart No. 6 Unsaturated alkyl amides of echinacea.

Formula Chart No. 7 Additional unsaturated alkyl amides of echinacea.

constituent glycine betaine, however, has been definitely identified as present. Subsequently the pyrrolizidine alkaloids tussilagine and isotussilagine were detected in E. purpurea and E. angustifolia (71). Some pyrrolizidine alkaloids are known to produce oxidative metabolites following ingestion that are carcinogenic. At present, however, there is no evidence of carcinogenicity for the echinacea alkaloids. (Formula Chart 8).

B. Plant Identification via Analysis of Solvent Soluble Components

Identification of echinacea material can be done conveniently even in powdered form and in extracts by HPLC and TLC examination of the

Formula Chart No. 8 Echinacea alkaloids.

Formula Chart No. 8 Echinacea alkaloids.

organic-soluble materials because they are easily separated and detected by UV. Alcoholic tinctures of echinacea contain caffeic acid derivatives and polyacetylenes (72). In particular, the roots of E. angustifolia and E. pallida contain 0.3-1.7% echinacoside (65,73) while extracts of the two plants can be distinguished in that 1,3- and 1,5-O-dicaffeoylquinic acids are present only in the roots of E. angustifolia (67). Cichoric acid and caftaric acid are significant E. purpurea root constituents but echinacoside is not present. Cichoric acid is a prominent constituent in the aerial parts of most echinacea species (57,75,76). The aerial parts of E. angustifolia and E. pallida also contain verbascoside (57). Des-rhamnosylverbascoside and 6-O-caffeoylechinacoside have been isolated from E. pallida (57). E. purpurea leaves also contain cichoric acid methyl ester, 2-O-caffeoyl-3-O-feruloyltartaric acid and 2-O-caffeoyl-3-O-cumaroyltartaric acid (54). Other work showed the presence of 2-O-caffeoyl-3-O-feruloyltartaric acid, 2,3-O-di-5-[a-carboxyl-|h-(3,4-dihy-droxyphenyl)ethylcaffeoyl] tartaric acid, and 2-O-caffeoyl-3-O-[5-{a-car-boxy-|h-(3,4-dihydroxyphenyl) ethyl}caffeoyll]tartaric acid in E. pallida (57). These variations in the levels of caffeic acid derived constituents are not regarded as being particularly meaningful in terms of immunostimulation but they clearly have excellent potential value in distinguishing among the various plants that might be commercialized under the name echinacea.

Numerous flavonoids, such as rutoside, have been identified in echinacea leaves (59,67,77). The general flavonoid content is about 0.38-0.48%.

Cichoric acid is especially abundant in the flowers of all Echinacea species examined (1.2-3.1%) and in the roots of E. purpurea (0.6-2.1%). Much less is present in the other aboveground parts (67). The content of cichoric acid is quite variable based on the season and the state of development of the plant. Quantitation is further complicated in that it is not stable during preparation of alcoholic tinctures and in expressed juices (73,75). Analysis of cichoric and caftaric acids by a micellar electrokinetic chromatographic method (MECK) apparently works well for extracts of E. purpurea (78). In this methodology a surfactant is used to produce micelles to facilitate the separations.

The major 2-ketoalkenes and 2-ketoalkynes of E. pallida roots are tetradeca-8Z-ene-11,13-diyn-2-one, pentadeca-8Z-11,13-diyn-2-one, penta-

deca-8Z,13Z-diene-11-yn-2-one, pentadeca-8Z-,13Z-diene-11-yn-2-one, pen-tadeca-8Z,11E,13Z-triene-2-one, and pentadeca-8Z-11Z-diene-2-one (4,67). These are found only in traces in E. angustifolia and E. purpurea. These unsaturated compounds readily autooxidize on storage to h-hydroxylated analogs even in root powder form (4). The differing concentration of these auto-oxidation products would provide a suitable means of distinguishing between E. pallida and E. angustifolia but their specific amounts would be time-dependent.

As detailed above, many alkamides are present in E. angustifolia roots where they are particularly abundant in quantity. Their structures are derived from undeca- and dodecanoic acid and differ from one another in the degree of unsaturation and the configuration of the double bonds (66). In E. purpurea roots there are characteristic differences in that most of the 11 alkamides possess a 2,4-diene moiety. This makes a convenient marker for distinguishing the source of the material (4,75). The aerial parts contain similar constituents (67,68). The concentration of most of these compounds is significantly less than 1% (0.001-0.151%). Alkamide levels in various parts of E. purpurea differ sufficiently to suggest that measurements of their distribution could be used to determine the origin of extracts (79). The photochemical instability of such compounds would require considerable caution in sample preparation and handling (80).

Pyrrolizidine alkaloids (tussilagine and isotussilagine) have been isolated from Echinacea species (81) but these seem to be of little interest from a chemotaxonomic viewpoint since they do not have a convenient UV chromophore.

A gas chromatographic method has been published that detects the presence of uracil herbicides in the roots of E. angustifolia. This would be useful in characterizing either cultivated or wild-picked echinacea materials (82). The gas chromatographic-mass spectroscopic methodology has also been applied to the analysis of echinacea mixtures themselves (83).

The variations in the kinds and amounts of solvent-soluble constituents from plant to plant part make identification and standardization of commercial preparations possible but their number and variation make this a complex undertaking. A recent study has analyzed the effect of some processing variables on the content of solvent-soluble constituents. Chopping altered the level of some alkamides slightly in E. purpurea roots but drying had no significant effect on the amounts detected. Levels of all alkamides fell by over 80% on storage at room temperature for 16 months and also fell significantly even when the plant material was stored at 18 °C (82).

Adulteration by Parthenium can also be detected readily by chromato-graphic methods based on the presence of sesquiterpene esters that are not present in echinacea (46,65,68).

In summary, despite the complexity of extracts, they are readily assayed and such assays can serve as surrogate markers for species verification. The lack of strong evidence supporting a causal relationship between an individual constituent and its presence in extracts reduces the value of such determinations. It seems prudent for the time being to perform biological assays as well.

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