Studies on the epoxidation of bromoallenes, biomimetic transannular rearrangements and the total synthesis of members of the Laurencia natural product family

Abstract

The research presented here regards the biosynthetic origins of several secondary metabolites isolated from red algae of the genus Laurencia. This thesis has been separated into two major parts, and includes an appendix cataloguing the experimental procedures and spectroscopic data. Part I covers the epoxidation of bromoallenes, as inspired by the previously unknown biosynthetic link between two natural products isolated from Laurencia obtusa, one bearing a bromoallene and the other an α,β-unsaturated ester. Employing model bromoallene 1 and a range of epoxidation methods, a procedure was developed that would generate α,β-unsaturated acids 2 in low, but reproducible yields. Isotopic labelling of the substrate with deuterium and carbon-13 allowed elucidation of the mechanism, by observation of the migration of these atoms.Part II of this thesis reports the completion of the total synthesis of a range of Laurencia secondary metabolites. The initial targets of this project proved to be unobtainable, most likely due to the sensitivity of the allyl ether group under reductive conditions. An alternative route was successfully applied to bypass this problematic step, allow the synthesis of a range of Laurencia natural products and provide insights into their biosynthesis. Positive identification of these compounds was achieved by a Δδ analysis of the collected 1H & 13C NMR spectra, with that reported in literature.