RING-CLEAVAGE OF SULFUR HETEROCYCLES - HOW DOES IT HAPPEN

Sulfur heterocycles are common constituents of petroleum and liquids d erived from coal, and they are found in some secondary metabolites of microorganisms and plants. They exist primarily as saturated rings and thiophenes. There are two major objectives driving investigations of the microbial metabolism of organosulfur compounds. One is the quest t o develop a process for biodesulfurization of fossil fuels, and the ot her is to understand the fates of organosulfur compounds in petroleum- or creosote-contaminated environments which is important in assessing bioremediation processes. For these processes to be successful, cleava ge of different types of sulfur heterocyclic rings is paramount. This paper reviews the evidence for microbial ring cleavage of a variety of organosulfur compounds and discusses the few well-studied cases which have shown that the C-S bond is most susceptible to breakage leading to disruption of the ring. In most cases, the introduction of one or m ore oxygen atom(s) onto the adjacent C atom and/or onto the S atom wea kens the C-S bond, facilitating its cleavage. Although much is known a bout the thiophene ring cleavage in dibenzothiophene. there is still a great deal to be learned about the cleavage of other sulfur heterocyc les.