Summary:
During menopausal transition and after menopause, the production of natural
endogenous hormones, the estrogens, diminish causing to females, a wide range
of symptoms,
while is considered the main cause of hormone dependent syndrome (postmenopausal
syndrome). Plant derived compounds, also known as phytoestrogens (PEs), have
emerged as
a potential class of nonsteroidal molecules, which induce biological responses
in mammals,
mimicking or modulating the action of the endogenous estrogens (17β-estradiol,
estriol,
estrone), deputizing to some extent, the deficient protective effect of natural
hormones.
The Leguminosae family has a rich content of phytoestrogens, detected among a
vast
majority of plant species. Erythrina excelsa Baker - Leguminosae is a tree,
geographically
confined in sub-Saharan Africa, where is widely used in traditional African
medicine to
alleviate menopausal symptoms. Additionally, the extend biological evaluation
of the
ethanolic extract of stem bark of Erythrina excelsa provided scientific
evidence of its
significant estrogenic activity both in vitro (yeast estrogen screen-YES) and
in vivo.
(uterotrophic assay). Moreover, Onobrychis alba (Waldst. & Kit.) Desv. subsp.
laconica
(Orph. ex Boiss.) Hayek is a Greek endemic species, which according to the
previews
research of our laboratory, belongs to a genus that has revealed several
constituents with
estrogenic activity among other pharmacological properties.
Thus, the choice of plant material was based in our continuous effort to
discover new
phytoestrogens. The hereto subject of interest is the phytochemical
investigation, isolation
and structure elucidation of secondary metabolites with potential estrogenic
activity from
the stem bark of E. excelsa and the roots of O. alba subsp. laconica.
Noteworthy, both
species, have scarce or no scientific reports of our phytochemical and
pharmacological
interest.
Therefore, after the extraction, the present study was aimed firstly at the
qualitative
investigation, which was performed with analytical techniques such as TLC,
HPLC-PDA,
UHPLC-ESI-HRMS & HR-MS/MS, in order to identify the potential active components
in
both plant exracts. Chromatographic and spectrometric features as well as the
HRMS/MS
spectra and HRMS analysis in full scan, were incorporated for the
identification procedure.
Subsequent fractionation of the extracts with chromatographic techniques such
as HSCCC,
MPLC and preparative TLC led to the isolation of secondary metabolites. For the
structure
elucidation of the purified isolated compounds, phasmatometric (HRMS) and mostly
phasmatoscopic 1 & 2D NMR techniques, were employed.
Conclusively, the phytochemical study of the ethanolic extract of Erythrina
excelsa
led to the isolation and identification of 7 isoflavones, 1 coumestan and 1
prerocarpan,
where the majority of them are reported in the species, for the first time.
Respectively, 5
isoflavones, 6 coumestans, 4 arylobenzofurans, among them 7 new natural
products, were
isolated and identified for the first time in methanolic extract of Onobrychis
alba subsp.
laconica. Finally, 16 secondary metabolites of O. alba subsp laconica
dicloromethanic extract
were rapidly identified with the LC-HRMS-based dereplication method.
Overall, both extracts led to the isolation and elucidation of 23 secondary
metabolites, that belong to the chemical categories of phytoestrogens,
verifying not only the
traditional use but also the existing pharmacological evaluations. As a future
goal, the
bioactive compounds will be evaluated in order to establish their estrogenic
effects.
