Synthesis and Antibacterial Properties of Oligomeric Dehydrogenation Polymer from Lignin Precursors.

The lignin precursors of coniferin and syringin were synthesised, and guaiacyl-type and guaiacyl-syringyl-type oligomeric lignin dehydrogenation polymers (DHP and DHP-GS) were prepared with the bulk method. The carbon-13 nuclear magnetic resonance spectroscopy showed that both DHP-G and DHP-GS contained β-O-4, β-5, β-β, β-1, and 5-5 substructures. Extraction with petroleum ether, ether, ethanol, and acetone resulted in four fractions for each of DHP-G (C ₁₁ -C ₁₄ ) and DHP-GS (C ₂₁ -C ₂₄ ). The antibacterial experiments showed that the fractions with lower molecular weight had relatively strong antibacterial activity. The ether-soluble fractions (C ₁₂ of DHP-G and C ₂₂ of DHP-GS) had strong antibacterial activities against E. coli and S. aureus . The C ₁₂ and C ₂₂ fractions were further separated by preparative chromatography, and 10 bioactive compounds (G ₁ -G ₅ and GS ₁ -GS ₅ ) were obtained. The overall antibacterial activities of these 10 compounds was stronger against E. coli than S. aureus . Compounds G ₁ , G ₂ , G ₃ , and GS ₁ , which had the most significant antibacterial activities, contained β-5 substructures. Of these, G ₁ had the best antibacterial activity. Its inhibition zone diameter was 19.81 ± 0.82 mm, and the minimum inhibition concentration was 56.3 ± 6.20 μg/mL. Atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) showed that the antibacterial activity of G ₁ was attributable to a phenylcoumarin dimer, while the introduction of syringyl units reduced antibacterial activity.