Cyclization of Polyphenols from Natural Products: Potential Pharmacological and Toxicological Implications
| dc.contributor.advisor | Krol, Ed S | |
| dc.contributor.committeeMember | Bandy, Brian | |
| dc.contributor.committeeMember | Yang, Jian | |
| dc.contributor.committeeMember | Palmer, David | |
| dc.contributor.committeeMember | Manderville, Richard | |
| dc.creator | Dalio Bernardes da Silva, Gabriel | |
| dc.creator.orcid | 0000-0002-2249-9856 | |
| dc.date.accessioned | 2023-01-06T16:23:28Z | |
| dc.date.available | 2023-01-06T16:23:28Z | |
| dc.date.copyright | 2022 | |
| dc.date.created | 2022-12 | |
| dc.date.issued | 2023-01-06 | |
| dc.date.submitted | December 2022 | |
| dc.date.updated | 2023-01-06T16:23:29Z | |
| dc.description.abstract | Previously our group identified that the dicatechol lignan nordihydroguaiaretic acid (NDGA) can undergo spontaneous autoxidation and intramolecular cyclization at pH 7.4 to form a dibenzocyclooctadiene (cNDGA). We also observed that autoxidation of NDGA or cNDGA was required for inhibition of -synuclein aggregation in vitro, a protein associated with Parkinson’s disease. A number of dicatechol ethanes have been shown to inhibit -synuclein aggregation in vitro and we propose that the anti-aggregation effects are the result of autoxidation/ intramolecular cyclization. My first goal was to determine if dicatechol ethanes could spontaneously autoxidize/ cyclize and inhibit -synuclein aggregation in vitro. In order to assess the formation of 6-membered ring dicatechols, I synthesized and characterized three diphenylethane analogs with 0, 2 or 4 methyl groups on the 2-carbon linker. I determined that all of the analogs spontaneously cyclize at pH 7.4 into the corresponding dibenzocyclohexadienes which were also oxidatively labile and formed additional oxidation products. The rate of cyclization to form dibenzocyclohexadienes is 10-30 times faster than for dibenzocyclooctadienes and both the diphenylethanes and dibenzocyclohexadienes inhibit -synuclein aggregation in vitro. A second goal of my project was to study the metabolism of quebecol, a triphenylethane natural product isolated from maple syrup production which is under investigation as a chemopreventive and chemotherapeutic, although there are no reports on the hepatic metabolism of quebecol. In order to assess hepatic metabolism, I synthesized and isolated quebecol and investigated its in vitro metabolism in rat liver microsomes (RLM) and human liver microsomes (HLM). I anticipated that phase II metabolism would predominate, and I observed formation of three glucuronide metabolites in both RLM and HLM. To determine the hepatic contribution to first-pass glucuronidation, I validated an HPLC-UV method following FDA and EMA guidelines (selectivity, linearity, accuracy and precision) to quantify quebecol metabolism in microsomes. In vitro enzyme kinetics were performed for quebecol glucuronidation in HLM including 8 concentrations from 5-30 M. I determined a Michaelis-Menten constant (KM) of 5.1 M, intrinsic clearance (Clint) of 0.04 mL/min/mg and maximum velocity (Vmax) of 0.22 mol/min/mg. In contrast I was unable to detect any P450 metabolites of quebecol in either RLM or HLM. In spite of the presence of three phenols that could form para-quinone methides, glutathione (GSH) trapping experiments provided no evidence for reactive intermediate formation. To confirm the absence of para-quinone methides I attempted to prepare standards using MnO2 as oxidant and trapping with GSH. Rather than observe the expected para-quinone methides, instead I observed ortho-quinone formation resulting from MnO2-mediated dealkylation. Together with extensive phase II glucuronidation, this suggests that the risk of reactive intermediate formation from quebecol is negligible. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | https://hdl.handle.net/10388/14399 | |
| dc.language.iso | en | |
| dc.subject | Di-catechol diphenylethanes | |
| dc.subject | dibenzocyclohexadienes | |
| dc.subject | in vitro alpha-synuclein aggregation | |
| dc.subject | oxidative instability | |
| dc.subject | intramolecular cyclization | |
| dc.subject | vicinal dimethyl effect | |
| dc.subject | geminal dimethyl effect | |
| dc.subject | quebecol | |
| dc.subject | glucuronidation | |
| dc.subject | hepatic metabolism | |
| dc.subject | para-quinone methide | |
| dc.title | Cyclization of Polyphenols from Natural Products: Potential Pharmacological and Toxicological Implications | |
| dc.type | Thesis | |
| dc.type.material | text | |
| thesis.degree.department | Pharmacy and Nutrition | |
| thesis.degree.discipline | Pharmacy | |
| thesis.degree.grantor | University of Saskatchewan | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |