A Biosynthetically-Inspired Chemical Synthesis of Naturally Occurring Halogenated Medium Ring Ethers from Laurencia

Seaweeds and alga provide a rich source of naturally occurring bromine and chlorine (halogenated) containing natural products. In particular, Laurencia species provide such halogenated compounds as medium ring ethers (rings of 7,8 or 9-atoms consisting of one oxygen and the rest as carbon) that have traditionally been viewed as difficult to synthesize in a laboratory. Previously, the biogenesis of these compounds has been assumed to involve the cyclisation of an alcohol onto a reactive bromonium ion to create the medium ring. However, there are some unexplained difficulties with the currently proposed biogenesis. We now propose that alcohols are not the true biogenetic precursors. Consideration of the various configurations of the metabolites from Laurencia species allows a unifying biosynthetic scheme to be proposed from an alternative common precursor, which are spring-loaded to overcome the traditional difficulties associated with making medium-sized rings.