Isolation and Structure Elucidation of Three Dimeric A-type Proanthocyanidins from Empetrum Nigrum L.

Introduction. Urinary tract infections are a common group of diseases worldwide, affecting more than 150 million people every year. In about 30 % of patients with initial infection, UTI becomes chronic. Herbal medicines, along with synthetic diuretics and antibiotics, are widely used for the prevention and treatment of UTIs, which makes the search and isolation of various substances from plant materials an important task. The present study is devoted to the isolation of compounds belonging to the class of proanthocyanidins from the aerial part of the black crowberry (Empetrum nigrum L.).Aim. Method development for the isolation of individual dimeric type A proanthocyanidins from the aerial part of Empetrum nigrum and the elucidation of their chemical structure using modern physicochemical methods of analysis.Materials and methods. Shoots of Empetrum nigrum were collected next to the Saint Petersburg State Chemical-Pharmaceutical University Nursery Garden of Medicinal Plants (Leningrad region, Vsevolozhsky district, Priozerskoe highway, 38 km) in August 2019. Fraction analysis was performed through analytical high-performance liquid chromatography (HPLC) using a Prominence LC-20 (Shimadzu corp., Japan) equipped with a SPD-M20A diode-array detector, as well as by high performance thin layer chromatography (HPTLC) using a CAMAG HPTLC system (Switzerland). The isolation of compounds was carried out by open column chromatography using sorbents with different selectivity, as well as by preparative HPLC using a Smartline system (Knauer, Germany) equipped with a spectrophotometric detector. The structures of the isolated compounds were established by 1D and 2D NMR experiments (Bruker Avance III 400 MHz, Germany), as well as high-resolution mass spectrometry (HR-ESI-MS) (Bruker Micromass Q-TOF, Germany).Results and discussion. Using the developed methods, from the Empetrum nigrum shoots we managed to isolate and characterised three individual compounds belonging to the class of A-type proanthocyanidins. According to NMR and mass spectrometry data, compound 1 is epicatechin-(2β → O → 5, 4β → 6)-epicatechin, with an extremely rare type of intermonomer bond (2β → O → 5, 4β → 6). Compounds 2 and 3 are epicatechin-(2β → O → 7, 4β → 8)-epicatechin (procyanidin A2) and epicatechin-(2β → O → 7, 4β → 8)-catechin (procyanidin A1), respectively. All individual compounds (1-3) were found and isolated from Empetrum nigrum for the first time.Conclusion. As a result of the research, three individual compounds (A-type proanthocyanidins) were isolated from the aerial part of Empetrum nigrum. All individual compounds (1-3) were found and isolated from Empetrum nigrum for the first time. Future assessment of the isolated compounds biological activity is presumed.