Oxidative Properties of Lignan
Lignin Compounds
Lignin Monomers
Abstract
The lignin polymer is synthesized via oxidative coupling of three basic monomers: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. These three monomers each possess a phenol group that stabilizes the radical intermediate generated during the oxidation reaction. Two radicals dimerize together to create lignan, which is biologically active and currently being tested for pharmacological properties such as, antiallergy effect, analgesic effect, and stress reducing activity. HPLC was used to study the oxidation of coniferyl alcohol, the monomeric lignan, and validate the formation of dimers. The mechanisms of this dimer formation were also studied to better understand the oxidative coupling of the lignin monomers.
Science Seminar
Oxidation of Monomers
Standards of Lignan
Oxidation Reactions of Monomers
Beaker reactions with varying reaction conditions were completed to analyze the oxidation of each monomer. For each monomer, 100 mL of a 2 mM standard solution of the monomer was made using 50/50 dioxane/pH 5 buffer. Three reactions were then completed with varying concentrations of hydrogen peroxide in the presence of HRP. The first reaction was composed of 5 mL of the substrate, 10 µL of hydrogen peroxide (1 mM final concentration hydrogen peroxide) and 5 µL of HRP. The second reaction was composed of 5 mL of the substrate, 5 µL of hydrogen peroxide (0.5 mM final concentration hydrogen peroxide) and 5 µL of HRP. The third reaction was composed of 5 mL of the substrate, 5 µL of hydrogen peroxide (0.25 mM final concentration hydrogen peroxide) and 5 µL of HRP. These reactions were then analyzed on the HPLC for oxidation products of each monomer.
Lignan
Background
Lignan is formed from the oxidative coupling of two lignin monomers. The dimers are often linked between the beta-carbons on the side chain of each monomer. Many of the dimers stated often in literature possess this linking structure. These dimers have biological activity, whereas the larger structure of lignin does not. This allows them to have potential healths benefits associated with them. Some of these benefits are anti-microbial, anti-inflammatory, and antioxidant. The relationship between allergies and lignan has also been studied. It might be related to having an anti-histamine effect on allergy symptoms.
Cancer
Research is currently being done to study the relationship between cancer and lignan. Breast cancer has been studied the most, but other cancers such as prostate and ovarian are being researched. Currently there are no conclusions regarding those cancers, as the research is in beginning stages. Many studies are centered around whether consumption of flax seeds correlates to a reduction in the risk of breast cancer, as well as the mortality. The reason flax seeds are being researched is because they have the highest concentration of lignans. With breast cancer, it was found flax seed consumption did decrease the risk of breast cancer, as well as the mortality of breast cancer, in post-menopausal women. This is believed to be because the lignan acts as a competitive inhibitor to estrogen. Some lignans, such as matairesinol and lariciresinol, have structures similar to estrogen. This allows them to bind to the estrogen receptor on the cancer cell, therefore blocking estrogen from binding. This prevents further growth of the cancer.
Analysis of Monomer Oxidation
The reactions and the standards were analyzed on the HPLC using an acetonitrile (ACN) and 0.1% TFA in water gradient for 30 minutes. The first 15 minutes were ran at 100% water, 15-25 minutes were ran at an 100% ACN, and the remaining 5 minutes at 100% water. This method is saved as "Phenol_30m_02." This method was developed by Bradley Sturgeon and Chris Knutson. This method varies slightly from the method I used when I was analyzing lignin, but overall represents the same goal.
| Matairesinol | Coniferyl Alcohol | Pinoresinol |
The two lignans matiresinol and pinoresinol were chosen since these were mentioned repeatedly in literature. By doing standards of these lignans, they could potentially be identified in the chromatogram of coniferyl alcohol. By oxidizing coniferyl alcohol with hydrogen peroxide it is possible some of the radicals formed dimers via oxidative coupling. It could be determined whether the peaks later in the chromatogram of the coniferyl alcohol corresponded to one of the lignans. The peaks unfortunately did not correspond to either of the lignans analyzed. Other lignans should be chosen in order to determine which exist in the coniferyl alcohol oxidation chromatogram.