This study reports the first enzymatic synthesis leading to several oligomer analogues of poly[3-(3,4-dihydroxyphenyl)glyceric acid]. This biopolymer, extracted from plants of the Boraginaceae family has shown a wide spectrum of pharmacological properties, including antimicrobial activity. Enzymatic ring opening polymerization of 2-methoxycarbonyl-3-(3,4-dibenzyloxyphenyl)oxirane (MDBPO) using lipase from Candida rugosa leads to formation of poly[2-methoxycarbonyl-3-(3,4-dibenzyloxyphenyl)oxirane] (PMDBPO), with a degree of polymerization up to 5. Catalytic debenzylation of PMDBPO using H₂ on Pd/C yields poly[2-methoxycarbonyl-3-(3,4-dihydroxyphenyl)oxirane] (PMDHPO) without loss in molecular mass. Antibacterial assessment of natural polyethers from different species of Boraginaceae family Symhytum asperum, S. caucasicum,S. grandiflorum, Anchusa italica, Cynoglossum officinale, and synthetic polymers, poly[2-methoxycarbonyl-3-(3,4-dimethoxyphenyl)oxirane (PMDMPO) and PMDHPO, reveals that only the synthetic analogue produced in this study (PMDHPO) exhibits a promising antimicrobial activity against pathogenic strains S.aureus ATCC 25923 and E.coli ATCC 25922 the minimum inhibitory concentration (MIC) being 100 µg/mL.

This study reports the antimicrobial activities of the biopolymers poly[3-(3,4-dihydoxyphenyl)glyceric acid] (PDHPGA) and poly[2-methoxycarbonyl-3-(3,4-dihydroxyphenyl)oxirane] (PMDHPO), extracted from the six plants of Boraginaceae family: Symphytum asperum (SA), S. caucasicum (SC), S. gr and iflorum (SG), Anchusa italica (AI), Cynoglosum officinale (CO), and Borago officinalis (BO) collected in various parts of Georgia. The study revealed that the antibacterial activities were moderate, and biopolymers from only three plants showed activities against all tested bacteria. Biopolymers from CO stems as well as SC and AI did not show any activity except low activity against a resistant P. aeruginosa strain, which was the most resistant among all three resistant strains. On the other hand, the antifungal activity was better compared to the antibacterial activity. Biopolymers from BO stems exhibited the best activities with MIC/MFC at 0.37–1.00 mg/mL and 0.75–1.5 mg/L, respectively, followed by those from SG stems. Biopolymers from SC and AI roots showed antifungal activities against all six fungi, in contrast to the antibacterial activity, while biopolymers from CO stems and SA roots had activities against four fungi and one fungus, respectively. The sugar-based catechol-containing biopolymers from BO stems demonstrated the best activities among all tested biopolymers against T. viride, P. funiculosum, P. cyclpoium var verucosum, and C. albicans (MIC 0.37 mg/mL). In addition, biopolymers from SG stems were half as active against A. fumigatus and T. viride as ketoconazole. Biopolymers from all plant materials except for CO stems showed higher potency than ketoconazole against T. viride. For the first time, it was shown that all plant materials exhibited better activity against C. albicans, one of the most dreadful fungal species.

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.