Synthesis of analogues of nordihydroguaiaretic acid and their oxidative metabolism

Abstract

In order to investigate the structural features responsible for the cytotoxicity of the naturally occurring lignan nordihydroguaiaretic acid, the synthesis of four structural analogues of NDGA is proposed for the purpose of studying their oxidative metabolism. One analogue in particular (1), a mono-catechol analogue, is successfully synthesized employing a double Stobbe condensation approach. Following synthesis of this compound a series of oxidation experiments is performed consisting of: incubation in rat liver microsomes with and without the trapping agent glutathione (GSH), oxidation with mushroom tyrosinase, oxidation with silver oxide, and oxidation with horseradish peroxidase. Results are analyzed via HPLC and UPLC-MS. It is found that 1 does not autoxidize at pH 7.4 as NDGA does. Two products are produced during incubation of 1 in rat liver microsomes with UPLC-ESI(-)-MS results giving m/z of 879.2 and 574.18. This is consistent with 1 plus 2 GSH and 1 plus 1 GSH respectively; confirming 1 will oxidize to an electrophilic moiety. Oxidation with mushroom tyrosinase is found to produce high levels of product two with m/z 574.2. Oxidation with horseradish peroxidase is found to produce high levels of the m/z 879.2 product. Silver Oxide produced multiple products rather than the expected one major product, but most are found to be inconsistent with the products seen during rat liver microsomal incubation, and are not pursued.