A Practical Synthesis of Zosteric Acid : One Step Towards New Sustainable Antifouling Agent?

Zosteric acid is a secondary metabolite of the aquatic plant Zostera Marina, the most wide-ranging marine flowering plant in the Northern Hemisphere. In the last few years this compound stimulated a great deal of interest due to its demonstrated capability of hindering deleterious biofilm formation without exhibiting toxicity. Therefore zosteric acid represents a potential candidate for replacing toxic biocides employed in commercially available antifouling paints. Zosteric acid has been isolated from natural sources through extraction with MeOH-H2O mixtures or chemically synthesized from p-hydroxycinnamic acid (1). The extraction method affords only small amounts of the compound, whereas the chemical method suffers from limitations derived from the use of a corrosive reagent such as chlorosulfonic acid and toxic or dangerous solvents such as pyridine and diethyl ether.1 Moreover, the isolation procedure is quite troublesome affording zosteric acid in 50% yield after purification through ion-exchange resins, followed by evaporation of huge amounts of water. Scheme 1 We recently developed a new environmentally friendly method employing the complex Py.SO3 as a solid, stable, sulfating agent (Scheme 1). The desired compound was isolated as sodium salt in nearly quantitative yields by neutralization of the reaction mixture with aqueous NaOH, followed by addition of methanol to remove sodium sulphate formed as byproduct. Such a procedure can be easily scaled-up, thus providing a practical synthesis of sodium zosterate and zosteric acid derivatives to be used as substitutes of toxic compound in the formulation of new environmentally friendly antifouling paints. References [1] S. Alexandratos, US Patent, 5990336 (1999).