Enzymatic C-H Oxidation-Amidation Cascade in the Production of Natural and Unnatural Thiotetronate Antibiotics with Potentiated Bioactivity

The selective activation of unreactive hydrocarbons by biosynthetic enzymes has inspired new synthetic methods in C-H bond activation. Herein, we report the unprecedented two-step biosynthetic conversion of thiotetromycin to thiotetroamideC involving the tandem oxidation and amidation of an unreactive ethyl group. We detail the genetic and biochemical basis for the terminal amidation in thiotetroamideC biosynthesis, which involves a uniquely adapted cytochrome P450-amidotransferase enzyme pair and highlights the first oxidation-amidation enzymatic cascade reaction leading to the selective formation of a primary amide group from a chemically inert alkyl group. Motivated by the ten-fold increase in antibiotic potency of thiotetroamideC ascribed to the acetamide group and the unusual enzymology involved, we enzymatically interrogated diverse thiolactomycin analogues and prepared an unnatural thiotetroamideC analogue with potentiated bioactivity compared to the parent molecule.