Assessment of Chemical Composition of High Molecular Fractions from Myosotis arvensis and Myosotis micrantha (Boraginaceae) by Nuclear Magnetic Resonance Spectroscopy

Background: In our previous studies, we investigated water-soluble mucilaginous high molecular fractions (HMF) of medicinal plants Symphytum asperum, S. caucasicum, S. grandiflorum, S. officinale, Anchusa italica, Cynoglossum officinale, Borago officinalis, and Paracynoglossum imeretinum (Boraginaceae family).The water extracts of the aforementioned plants were fractionated using ultrafiltration with membrane filters having cut-off values of 1000 kDa or 500 kDa.This fractionation procedure allowed us to remove most polysaccharides and obtain water-soluble HMFs.The main chemical constituent of HMFs of plants described above was found to be biologically active unique caffeic acid-derived biomacromolecule poly[oxy-1carboxy-2-(3,4-dihydroxyphenyl)ethylene] that is poly [3-(3,4-dihydroxyphenyl)glyceric acid] (PDHPGA).Objectives: Within our ongoing search for biologically active biopolymers in plant species belonging to different genera of the Boraginaceae family, the present study aimed to isolate and investigate water-soluble high-molecular fractions (Mr>500 kDa) of roots for Myosotis arvensis (MA) and stems-roots for Myosotis micrantha (MM) (HMF-MA and HMF-MM, respectively) to study their main chemical constituents and carry out their structure elucidation.Methods: As described in some earlier publications, HMF-MA and HMF-MM were isolated from water mucilage extracts using ultrafiltration with a membrane filter having a cut-off value of 500 kDa.Analyses of HMF-MA and HMF-MM were conducted using non-destructive physicochemical instrumental methods, including Fourier Transform Infrared Spectroscopy (FTIR), a method considered one of the most effective for identifying functional groups, and Nuclear Magnetic Resonance (NMR) techniques, which are powerful tools for elucidating the structure of chemical compounds.Results: The NMR spectroscopy revealed that the main chemical constituent of HMF-MA and HMF-MM is a complex pectin-type polysaccharide.Conclusions: Thus, the high-molecular fraction of Myosotis arvensis and Myosotis micrantha (Mr > 500 kDa) does not contain biologically active PDHPGA, and its main chemical component is a pectin-type polysaccharide, acetylated rhamno-arabino-galacto-galactopyranosyluronan, where carboxyl groups of galacturonic acid are partially methylated.