Despite the limited geographic range of Eranthis plants, it is possible to search for active substances, develop methods for biological and chemical synthesis of the isolated substances, and create a finished therapeutic substance based on them. Seven out of ~14 species found in Asia and parts of Europe have been studied to various degrees. Here, data are presented on the diversity of sets of chromones, furochromones, triterpene saponins, coumarins, and other classes of secondary metabolites of Eranthis species according to the literature. For new compounds—isolated from Eranthis for the first time—structural formulas are also provided.
1. Introduction
According to molecular and morphological data, the tribe Cimicifugeae Torrey & Gray belongs to the family Ranunculaceae Juss. and includes four recognized genera and ~49 species:
Actaea L. (32 species),
Anemonopsis Siebold et Zucc. (one species),
Beesia Balf. f. et W. W. Sm. (two species), and
Eranthis Salisb. (14 species)
[1,2,3][1][2][3]. Most of these species occur mainly in the northern hemisphere and are perennial herbs
[4]. The taxonomic position of the genera
Eranthis and
Beesia has been a matter of systematic uncertainty within the tribal rank in the Ranunculaceae family. According to morphological information,
Beesia has been assigned to three different tribes (Helleboreae DC., Actaeeae Spach, and Trollieae Schröd.) by intuitive taxonomic techniques but has seldom been included in cladistic analyses
[5,6,7][5][6][7]. By contrast, the
Eranthis genus has consistently been assigned to the Helleboreae tribe or as the only genus to the tribe Eranthideae T. Duncan & Keener in morphological classifications but always has been a sister taxon to plants of the Actaeeae tribe in cladistic analyses
[8]. The genus
Eranthis consists of 8–14 species growing in southern Europe and temperate Asia
[9,10,11][9][10][11]. Traditionally, the genus has been subdivided into two sections:
Eranthis sect.
Eranthis and
E. sect. Shibateranthis (Nakai) Tamura
[12]. The type section
Eranthis is characterized by plants with tubers, yellow sepals, and emarginate or slightly bilobate upper petal margins without pseudonectaries (
Figure 1)
[6,11][6][11]. The section
Eranthis in Europe includes
E. hyemalis (L.) Salisb. and
E. bulgarica (Stef.) Stef., whereas in Southwest and West Asia, it includes
E. cilicica Schott et Kotschy,
E. kurdica Rukšāns,
E. longistipitata Regel, and
E. iranica Rukšāns et Zetterl.
[13,14,15,16][13][14][15][16]. The section Shibateranthis has long-lived tubers, white sepals, and bilobate or forked petal margins with pseudonectaries (
Figure 1)
[6,17][6][17]. Representatives of this section have a natural geographic range in temperate North and East Asia (
E. albiflora Franch.,
E. byunsanensis B.Y. Sun,
E. lobulata W.T.Wang,
E. pinnatifida Maxim.,
E. pungdoensis B.U. Oh,
E. sibirica DC.,
E. stellata Maxim., and
E. tanhoensis Erst)
[10,11][10][11].
Figure 1. Species of the genus Eranthis. (A) E. longistipitata, (B) E. cilicica, (C) E. hyemalis, (D) E. sibirica, (E) E. tanhoensis, and (F) E. stellata.
Plants of the tribe Cimicifugeae are some of the richest sources of various active ingredients and of therapeutic and health-promoting substances. The value of the constituents has been confirmed by many years of use in East Asian countries in folk medicine. Thus, it is important to integrate new technologies into research on Cimicifugeae, both for the sustainable use of pharmaceutical resources from Cimicifugeae and for a search for new compounds with potential clinical efficacy and fewer adverse effects
[18,19,20][18][19][20]. In the tribe Cimicifuga, representatives of the genus
Actaea are the most frequently studied plants in the world of science. Nonetheless, little is known about the chemical profile and biological activity of other representatives of Cimicifugeae:
Beesia and
Anemonopsis. In recent decades, new information has been obtained about the chemical profiles of (and biological effects of extracts and individual compounds from)
Eranthis species, which are early flowering geophytes with a limited geographic range.
2. Phytocomponents Identified in Eranthis Plants and Their Chemotaxonomic Significance
2.1. Chromones
Since the 1960s, from some
Eranthis species, a series of substances has been isolated that represents an important class of oxygen-containing heterocyclic compounds that are derivatives of benzo-γ-pyrone: chromones. Their isolation has been performed by various chromatographic methods, and the structures of individual compounds have been investigated by 1-dimensional (H-NMR) and 2-dimensional nuclear magnetic resonance (C-NMR) spectroscopy. In structure, chromones are similar to flavonoids and coumarins but are substantially less common in the wild. Chromones can give rise to hydroxy- and methoxy-derivatives and can attach a sugar moiety, whereas after condensation with benzene, pyran, or furan rings, they can be transformed into a variety of benzo-, pyrano-, or furochromones, respectively. Compounds from the class “simple furochromones and chromones” are most often found in
Eranthis species; chromones have been detected in underground parts, whereas furochromones have been found in underground and aboveground parts (
Table 1).
Table 1.
Chemical constituents of the genus
Eranthis
(all classes of metabolites identified to date: vertical subdivisions in the table).