7 - The Halogenated Sulphatides

Abstract

This chapter discusses the halogenated sulfatides. The marine organisms that have yielded halogenated compounds have yielded nearly exclusively bromo compounds, with occasional exceptions. It is possible to obtain a bromo analogue of a natural chloro compound in almost all cases. Such analogues are obtained by culturing the microorganism in a chloride-free medium, and adding bromide in appropriate concentration. The chapter discusses the chlorinated alkyl sulphates of Ochromonas danica. These curious lipids, chlorinated alkyl sulphates, are the only known chlorolipids to date. They are rather well characterized, and have only been reported in phytoflagellates. In addition to unusual chemical structures, these substances are also characterized by an unusual physiology. A very significant aspect of these unusual lipids is the structure of the alkyl disulphates. The occurrence of the second sulfate ester on the 14 or 15 carbon of an alkyl chain implies that the lipid molecule has polar groups at both ends of the chain. This is unique in lipid chemistry. The fact that all other lipids whose structures are known have polar groups at only one end of the aliphatic chain is a foundation stone of the current theories of membrane structure. This unique structure has broad ramifications as a membrane component.