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Six new and four known dihydrochalcone glucoside derivatives (1-10), the phenylpropanoid coniferin (11), and the lignans (+)-pinoresinol (12) and lariciresinol (13) were isolated from the subaerial plant parts of Thonningia sanguinea in the course of a screening campaign for new antidiabetic lead compounds. The structures of the new substances were elucidated by HRESIMS, NMR, GC-MS, and ECD data evaluation. 2'- O-(3-Galloyl-4,6- O- S-hexahydroxydiphenoyl-β-d-glucopyranosyl)-3-hydroxyphloretin (4), 2'- O-(4,6- O- S-hexahydroxydiphenoyl-β-d-glucopyranosyl)phloretin (5), 2'- O-(3- O-galloyl-4,6- O- S-hexahydroxydiphenoyl-β-d-glucopyranosyl)phloretin (6), and thonningianin B (9) showed moderate protein tyrosine phosphatase-1B inhibition in an enzyme assay (IC values ranging from 19 to 25 μM), whereas thonningianin A (10) was identified as a more potent inhibitor (IC = 4.4 μM). The observed activity differences could be explained by molecular docking experiments. The activity of 10 could further be confirmed in HEPG2 liver carcinoma cells, where the compound was able to increase the level of phosphorylated insulin receptors in a concentration-dependent manner.

Thonningia sanguinea is a parasitic herb widely used in traditional African medicine. Dihydrochalcone glucosides (unsubstituted, substituted with hexahydroxydiphenoyl or galloyl moieties) are the main constituents in the subaerial parts of this plant. In the present study, purification of the six major compounds from a methanol extract of the plant's subaerial parts was achieved by centrifugal partition chromatography.A first dimension centrifugal partition chromatography separation with the solvent system methyl tert-butyl ether/1,2-dimethoxyethane/water (1:2:1) in the ascending mode enabled the isolation of the two major bioactive compounds thonningianin A and B from 350 mg of methanol extract within only 16 min with respectable yields (25.7 and 21.1 mg), purities (87.1 and 85%), and recoveries (71.2 and 70.4%). Using a multiple heart-cutting strategy, the remaining four major dihydrochalcone glucosides of the extract were further separated in a second dimension centrifugal partition chromatography with the solvent system ethyl acetate/1,2-dimethoxyethane/water (2:1:1) in the descending mode with high purities (88.9-98.8%).

Thonnigia sanguinea is a plant widely used in traditional African medicine against a variety of diseases. The obligate parasite is growing throughout tropical African forests and utilizes a large variety of hosts. Dihydrochalcone glucoside derivatives isolated from the subaerial parts of this plant were identified as potential antidiabetic lead compounds. In this study, an ultrahigh-performance liquid chromatographic method coupled with a photodiode array detector was developed for the quantitation of six major dihydrochalcone derivatives. The analytes were baseline separated in complex samples within 14 minutes on a Phenomenex Luna Omega 1.6 µm C18 column using a mobile phase consisting of water and acetonitrile (each + 0.01% trifluoroacetic acid) in gradient elution. Method validation confirmed the selectivity, linearity (R2 ≥ 0.9992), precision (inter-day ≤ 1.98%, intraday ≤ 2.00%), and accuracy (recovery rates of 97.4 – 106.3% for all analytes). At 280 nm, the LODs and LOQs were found to be lower than 1.42 and 4.30 µg/mL, respectively. Eight plant batches from the northern Angolan province of Uíge (collected in the wild or bought on markets) were extracted with methanol using an ultrasound-assisted extraction protocol and subsequently analyzed with the validated method. Results indicated high contents of dihydrochalcone glucosides in all eight samples. Most notably, the two bioactive constituents thonningianin A and B were present in fairly large amounts (2.42 – 5.35 w%).

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