The Isolation and oxidative coupling of lignans

Abstract

The first part of this work discusses the results of a re-examination of the lignan constituents contained in extracts of the wood of the New Zealand podocarp, Dacrydium intermedium. The structures and absolute configurations of five new lignans isolated from these extracts have been formulated on the basis of spectroscopic and chemical evidence. X-Ray crystallography has been used to confirm the structure assigned to one of the new lignans. In addition, the structure of one of the three lignans isolated during a previous investigation of the lignans of D. intermedium has been revised. In the second part of this work the non-phenolic and monophenolic oxidative coupling of a number of natural and synthetic diarylbutane lignans has been investigated. Oxidative coupling with a thallium (III) oxidant prepared in situ from thallic oxide and trifluoroacetic acid has been found to efficiently convert these lignans into either dibenzocyclooctadiene or aryltetralin lignans. Evidence is presented which indicates that the nature of the aromatic substituents in the parent diarylbutane lignans plays an important role in determining the outcome of oxidative coupling. The dibenzocyclooctadiene lignan prepared from oxidative coupling of dimethylmatairesinol has been converted into a compound which has significant in vitro antileukemic activity.