Biologically Active Polyethylene Glycol-Based Multiple-Catechol-Containing Biopolymer Poly[3-(3,4-dihydroxyphenyl) glyceric acid] from Different Medicinal Plants of Boraginaceae Family

High molecular weight (>1000 kDa or >500 kDa) water-soluble preparations (HMPs) from Symphytum asperum, S. caucasicum, S. officinale, S. grandiflorum, Anchusa italica, Cynoglossum officinale, Borago officinalis, and Paracynoglossum imeretinum (Boraginaceae) were obtained. The main chemical constituent of these HMPs is the first and only representative of a previously unreported class of natural polyethers — a novel poly[oxy-1-carboxy-2-(3,4-dihydroxyphenyl)ethylene], also known as poly[3-(3,4-dihydroxyphenyl)­glyceric acid] (P-DGA). The structure elucidation of P-DGA was performed using data from various nuclear magnetic resonance (NMR) techniques, including liquid-state 1H, 13C NMR, two-dimensional (2D) homonuclear gCOSY, two-dimensional (2D) heteronuclear 1H/13C gHSQCED, two-dimensional (2D) DOSY (Diffusion-ordered spectroscopy), and solid-state 13C NMR spectra. The polyoxyethylene (polyethylene glycol) (PEG) chain serves as the backbone of this biopolymer, with a residue of 3-(3,4-dihydroxyphenyl)glyceric acid functioning as the repeating unit. The 3,4-dihydroxyphenyl (catechol) and carboxyl groups consistently substitute for two carbon atoms in the PEG backbone chain. Hence, P-DGA represents a unique class of natural polyethers. Each repeating trifunctional structural unit of P-DGA contains two phenolic hydroxyl groups in the ortho position and one carboxyl group. The multifunctionality of P-DGA likely explains its wide spectrum of biological activities, including anti-complementary, antioxidant, anti-inflammatory, burn and wound healing, antimicrobial, and anti-cancer properties.