The use of proton NMR spectroscopy allows the analysis of complex multi-component mixtures such as plant extracts by simultaneous quantification of all proton-bearing compounds and consequently all relevant substance classes. Since the spectra obtained are too complicated to be analysed visually, the classification of spectra was carried out using multivariate statistical methods. The spectroscopic data of various extracts of St. John's wort (Hypericum perforatum) samples derived from 4 different accessions extracted with 6 distinct solvents were chemometrically evaluated and calibrated using the partial least square (PLS) algorithm. In a first approach, we found a consistent correlation for the spectroscopic pattern of the extracts and the corresponding IC (50) values derived from non-selective binding to opioid receptors. Consequently, the multivariate data analysis was used to predict the pharmacological efficacy of further St. John's wort extracts on the basis of their proton NMR spectra. In a second approach a PLS 2 model was used to predict the biological activity for eight St. John's wort extracts based on two pharmacological data sets: (i) non-selective binding to opioid receptors and (ii) antagonist effect at corticotrophin-releasing factor type 1 (CRF (1)) receptors. The PLS 2 model confirmed the useful application of the presented approach to assess the quality of medicinal herbs and extracts by spectroscopic analysis derived from bioactivity-related quality parameters.
Two new hydrolyzable tannins, isoterchebulin (1) and 4,6-O-isoterchebuloyl-d-glucose (2), together with
six known tannins, 3−8, were isolated from the bark of Terminalia macroptera
. Their structures were
elucidated by extensive 1D and 2D NMR studies, MS, and chemical transformations. Biological activities
of all compounds were evaluated against the snail Biomphalaria glabrata, the bacteria Bacillus subtilis
and Pseudomonas fluorescens, the nematode Caenorhabditis elegans, and four cancer cell lines (Hep G2,
MCF-7/S, MDA-MB-231, and 5637 cells). All compounds except 3 showed antimicrobial activities against
B. subtilis (MIC 8−64 μg/mL), whereas only 1 was active against C. elegans (100 μg/mL) and B. glabrata
(LC100 = 60 μg/mL). 3 and 8 were toxic against 5637 cells with LC50 = 84.66 and 41.40 μM, respectively.
Application of both LC-MS and LC-NMR to a partially purified extract of Vernonia fastigiataled to the direct identification of antibacterial sesquiterpene lactones 1-9 without isolation of individual compounds. The rapid structural analysis of both major and minor components of this class of compounds demonstrated the power of structure-guided screening as a complementary method to assay-guided screening.
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