Isolation and structural elucidation of 3',4',5'-trimethoxyflavone from the flowers of Primula veris

Comparative Phytochemical Analyses of Flowers from Primula veris subsp. veris Growing Wild and from Ex Situ Cultivation in Greece

In the last decades, Primula veris subsp. veris (roots and flowers) has been over harvested through legal and illegal ways in Greece, due to its extremely high commercial demand, as it is used in industry because of its well-known therapeutic properties. As ex situ cultures of the plant have been already developed, in the current comparative study, the herbal teas (infusions) from both flowers of cowslip growing wild in the Prespa Lake Park (NW Greece), and from ex situ propagated and cultivated plant material, have been investigated, with the ultimate goal of assessing them qualitatively. Furthermore, through classic phytochemical studies, the ten most abundant metabolites, belonging to the chemical categories of flavonol-glycosides and methoxy flavones, have been identified and structurally determined. The chemical profile of both infusions has been further analyzed through UHPLC-HRMS, showing that they show only light differences. The total phenolic content (TPC) of both studied samples (wild and ex situ cultivation), was determined by the Folin-Ciocalteau method, followed by an antioxidant activity assay though DPPH where, in both cases, wild plants exerted higher phenolic load and stronger antioxidative properties. According to the reported results, it could be proposed that the ex situ cultivated plant material could facilitate the mass production of plants and the sustainable cultivation of cowslip in the Greek mountains.

Two Novel Natural Flavonoids from Primula palinuri

The farinose exudate produced by Primula palinuri was found to consist of 12 flavones at least. Two of them are novel natural compounds, 2′-hydroxy-2-methoxychalcone and 8,2′,5′-trihydroxyflavone 5′-benzoate. The structure was determined by analysis of MS and 2D NMR spectral data and spectral comparison with the known compounds.

Phytochemistry of European Primula species

The genus Primula is the largest among the Primulaceae and is widespread mainly in the cold and temperate regions of the Northern Hemisphere. Since the beginning of the Twentieth century, several studies on the phytochemical composition of different species of Primula have been carried out. The main constituents examined were tissue and epicuticular flavonoids and saponins, which are of therapeutic significance. Only in recent years studies of the volatiles emitted by leaves and flowers have been carried out as well, but they are restricted to a small number of species. Only a few authors have documented the morphology and function of glandular trichomes in relation to the production of flavonoids and volatile organic compounds (VOCs). The use of Primula in folk medicine is described in the literature. Investigation of the biological and pharmacological activities of Primula are reported. This study aims at providing a collection of publications on the genus Primula along with a critical revision of literature data. It focuses on the possible taxonomic significance of the secondary metabolites and on their ecological role as attractors for pollinators and deterrents against herbivores and parasites, in order to build the base for further studies.

Farinose alpine Primula species: phytochemical and morphological investigations

This work investigated the epicuticular and tissue flavonoids, the volatiles and the glandular trichome structure of the leaves of four species of Primula L. that grow in the Italian Eastern Alps. Primula albenensis Banfi and Ferlinghetti, P. auricula L., P. farinosa L., P. halleri Gmelin produce farinose exudates that are deposited on the leaf surface as filamentous crystalloids. In addition to compounds already known, a new flavone, the 3,5-dihydroxyflavone, was isolated from the acetone extract of leaf farinas and three new flavonol glycosides, 3'-O-(β-galactopyranosyl)-2'-hydroxyflavone, isorhamnetin 3-O-α-rhamnopyranosyl-(1→3)-O-[α-rhamnopyranosyl-(1→6)]-O-β-galactopyranoside, quercetin 3-O-α-rhamnopyranosyl-(1→3)-O-[α-rhamnopyranosyl-(1→6)]-O-β-galactopyranoside, were isolated from the MeOH extract of the leaves. All the structures were elucidated on the basis of their (1)H and (13)C NMR data and 2D NMR techniques, as well as on HPLC-MS. The leaf-volatiles emitted by these Primula species were mainly sesquiterpene hydrocarbons, with the exception of P. albenensis, which produced almost exclusively a non-terpene derivative; P. halleri flowers were also examined and the volatiles emitted by the flower parts (corolla and calyx) were compared with the corresponding leaves.

Rare Flavones from the Glandular Leaf Exudate of the Oxlip, Primula Elatior L

5,6,2′,3′,6′-Pentamethoxyflavone (1), together with 3′,5′-dihydroxy-4′-methoxyflavone (2), 2′-methoxyflavone, 3′-methoxyflavone, 3′,4′-dimethoxyflavone, 2′,5′-methoxyflavone, 3′-hydroxy-4′,5′-dimethoxyflavone, 3′,4′,5′-trimethoxyflavone, and 3′-hydroxy-4′,5′-methylenedioxyflavone were found in the leaf exudate of the oxlip, Primula elatior (Primulaceae). The structures of flavones 1 and 2 were substantiated by 2D NMR spectroscopy.

Lipophilic flavones of Primula veris L. from field cultivation and in vitro cultures

Ten lipophilic flavones were isolated from the leaves of Primula veris from field cultivation - the newly described 3'-hydroxy-4',5'-dimethoxyflavone and 3'-methoxy-4',5'-methylenedioxyflavone, the previously known from chemical synthesis 3',4'-dimethoxyflavone, 2',5'-dimethoxyflavone, and also flavone, 2'-hydroxyflavone, 2'-methoxyflavone, 3'-methoxyflavone, 3',4',5'-trimethoxyflavone and 5,6,2',6'-tetramethoxyflavone (zapotin) which were previously known from plants. The same flavones were found in the leaves of P. veris obtained by in vitro propagation. The structural assignments were derived from (1)H NMR, (13)C NMR, EIMS and UV spectral data and the influence of B-ring oxygen substituents on the C-2, C-3 and H-3 NMR resonances in flavones unsubstituted in the A ring is taken into consideration.

Evaluation of detection methods for the reversed-phase HPLC determination of 3',4',5'-trimethoxyflavone in different phytopharmaceutical products and in human serum

Quantitative determination of the major compound, 3',4',5'-trimethoxyflavone (1), in plant extracts, in tablets of Flos and of Radix Primulae veris and in human serum has been accomplished using reversed-phase HPLC with UV, fluorescence and mass spectrometric (MS) detection. Compared to UV detection, fluorescence detection showed greater selectivity, was 10-fold more sensitive and allowed the determination of 1 in human serum after sample pre-treatment by solid-phase extraction. MS detection of 1 using electrospray ionisation (ESI) interface could be improved by substituting trifluoroacetic acid with the more polar and less conductive additive acetic acid, giving rise to a 230-fold improvement in analyte detectability at the cost of an increase of only 45% in the peak width of the eluting peak at its half height. Further optimisation of the acetic acid concentration showed the highest signal intensity at 1.25% for HPLC-atmospheric pressure chemical ionisation (APCI)-MS and at 0.75% for HPLC-ESI-MS. The optimised MS method proved to be extremely selective, 50 times more sensitive than UV detection and 5 times more sensitive than fluorescence detection. Furthermore, fragment-ion spectra produced by collision induced dissociation-MS have been used as "fingerprints" for identifying compounds in the highly complex mixtures examine.