Laccase Catalyzed Synthesis of Iodinated Phenolic Compounds with Antifungal Activity

Abstract

Iodine is a well known antimicrobial compound. Laccase, an oxidoreductase which couples the one electron oxidation of diverse phenolic and non-phenolic substrates to the reduction of oxygen to water, is capable of oxidizing unreactive iodide to reactive iodine. We have shown previously that laccase-iodide treatment of spruce wood results in a wash-out resistant antimicrobial surface. In this study, we investigated whether phenolic compounds such as vanillin, which resembles sub-structures of softwood lignin, can be directly iodinated by reacting with laccase and iodide, resulting in compounds with antifungal activity. HPLC-MS analysis showed that vanillin was converted to iodovanillin by laccase catalysis at an excess of potassium iodide. No conversion of vanillin occurred in the absence of enzyme. The addition of redox mediators in catalytic concentrations increased the rate of iodide oxidation ten-fold and the yield of iodovanillin by 50%. Iodinated phenolic products were also detected when o-vanillin, ethyl vanillin, acetovanillone and methyl vanillate were incubated with laccase and iodide. At an increased educt concentration of 0.1 M an almost one to one molar ratio of iodide to vanillin could be used without compromising conversion rate, and the insoluble iodovanillin product could be recovered by simple centrifugation. The novel enzymatic synthesis procedure fulfills key criteria of green chemistry. Biocatalytically produced iodovanillin and iodo-ethyl vanillin had significant growth inhibitory effects on several wood degrading fungal species. For Trametes versicolor, a species causing white rot of wood, almost complete growth inhibition and a partial biocidal effect was observed on agar plates. Enzymatic tests indicated that the iodinated compounds acted as enzyme responsive, antimicrobial materials.

A Key Role for Apoplastic H2O2 in Norway Spruce Phenolic Metabolism

“…These results suggest an important role for apoplastic H 2 O 2 in extracellular lignin production. Moreover, as iodide does not inhibit laccase activity in vitro (Ihssen et al, 2014), the results suggest that peroxidases are crucial for monolignol oxidation during extracellular lignin formation. To investigate the effects of apoplastic H 2 O 2 scavenging on phenolic metabolism, a time-course sampling of cells and culture medium from the various types of culture (Supplemental Fig.…”

Improvement of the Antifungal Activity Against Botrytis Cinerea of Syringic Acid, a Phenolic Acid From Grape Pomace

“…Antioxidant, antitumor, and anti-depressive compounds have been synthesized using this enzyme [8][9][10][11] . Additionally, this enzyme has been recently used for the synthesis of antifungal compounds 12 .…”

Enzymatic biocatalysis of bamboo chemical constituents to impart antimold properties

“…In an innovative and seminal research, Schubert et al (2012) and Ihssen et al (2014) demonstrated that KI could be bound to wood using the laccase-mediator system. In this way, KI would then provide antimicrobial surfaces even after leaching.…”

“…In this way, KI would then provide antimicrobial surfaces even after leaching. The research of Schubert et al (2012) and Ihssen et al (2014) was some of the first to be conducted which demonstrated a new and bio-based technology to fix iodine residues onto Norway spruce wood for potential protection in a safe and environmentally acceptable manner. Their work was focused on wood rather than bamboo or grasses but demonstrated the effectiveness of such treatments against a wide variety of fungi including blue-stain, wood decay, yeasts, and gram-positive and gram-negative bacteria.…”