Phenological Variations in the Content of Polyphenols and Triterpenoids in Epilobium angustifolium Herb Originating from Ukraine

Abstract

The composition of secondary metabolites undergoes significant changes in plants depending on the growth phase and the influence of environmental factors. Therefore, it is important to determine the harvesting time of plant material for the optimum secondary metabolite profile and therapeutic activity of the primary material. The shoots of Epilobium angustifolium are used as a healing tea due to the presence of polyphenolic compounds. The aim of this study was to assess the composition of phenolic compounds and triterpenoid saponins in E. angustifolium leaves and flowers and to estimate the dynamics of their content depending on the flowering phase. Qualitative and quantitative characterisation of polyphenols and triterpenoids in E. angustifolium samples from Ukraine of three flowering phases were performed using the high-performance liquid chromatography photo diode array (HPLC-PDA) method. During the present study, 13 polyphenolic compounds and seven triterpenoids were identified in the plant material. It was noted that the largest content and the best polyphenol profile was in late flowering. The most important polyphenolic compounds in the plant material were chlorogenic acid, hyperoside, isoquercitin, and oenothein B. The triterpenoid profile was at its maximum during mass flowering, with corosolic and ursolic acids being the dominant metabolites. The results of the analysis revealed that the quantity of many of the tested metabolites in the raw material of E. angustifolium is dependent on the plant organ and flowering phase. The largest content of most metabolites in the leaves was in late flowering. In the flowers, the quantity of the metabolites studied was more variable, but decreased during mass flowering and increased significantly again in late flowering. The results show that E. angustifolium raw material is a potential source of oenothein B and triterpenoids.

Keywords: Chamaenerion angustifolium; biologically active compounds; flowering phase; phenology.

Figure 1

Representative HPLC-DAD chromatograms of polyphenols of Epilobium angustifolium flowers harvested during early flowering. Peak assignments: 1—gallic acid; 2—neochlorogenic acid; 3—oenothein B; 4—chlorogenic acid; 5—oenothein A; 6—ellagic acid; 7—rutin; 8—hyperoside; 9—isoquercitrin; 10—guaijaverin (quercetin-3-O-arabinopyranoside); 11—quercitrin; 12—afzelin (kaempferol-3-O-rhamnoside); 13—quercetin.

Figure 2

Representative HPLC-DAD chromatograms (λ = 205 nm) of triterpenoid acids and neutral triterpenoids of Epilobium angustifolium flowers harvested during early flowering. Peak assignments: 1—maslinic acid; 2—corosolic acid; 3—oleanolic acid; 4—ursolic acid; 5—betulin; 6—erythrodiol; 7—uvaol.

Figure 3

Dynamics of gallic acid (A), oenothein B (B), rutin (C), hyperoside (D), and guaijaverin (E) and the total content of polyphenols (F) in Epilobium angustifolium flowers and leaves in different flowering phases.

Figure 4

Dynamics of maslinic (A), corosolic (B), and ursolic (C) acids and the total content of triterpenoids (D) in Epilobium angustifolium flowers and leaves in different flowering phases.

Figure 5

The proposed biosynthetic pathway of ellagitannins (oenothein B) in E. angustifolium (modified from data in [39,42]). The metabolic pathway starts with erythrose-4-phosphate and phosphoenolpyruvate (not shown in the figure). The enzymes that catalyse the individual steps from erythrose-4-phosphate and phosphoenolpyruvate are the following: 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase, 3-dehydroquinate synthase, dehydroquinate dehydratase/shikimate dehydrogenase. Further, the biosynthetic steps involve: DQD/SDH—dehydroquinate dehydratase/shikimate dehydrogenase; DHS—dehydratase; SD—shikimate dehydrogenase; SK—shikimate kinase enzyme; EPSPS—5-enolpyruvylshikimate 3-phosphate synthase; CS—chorismate synthase; FMNH2—reduced flavin mononucleotide; PAL—phenylalanine ammonia lyase; C4H—cinnamate 4-hydroxylase; 4CL—4-coumaroyl-CoA ligase; CHS—chalcone synthase; CHI—chalcone isomerase; chorismate mutase prephenate aminotransferase; arogenate dehydrogenase; arogenate dehydratase; PCA—hydroxylase.