Oxygen heterocycles—in particular, tetrahydropyrans (THPs) and tetrahydrofurans—are common structural features of many biologically active polyketide natural products. Mupirocin is a clinically important antibiotic isolated from Pseudomonas fluorescens and is assembled on a THP ring, which is essential for bioactivity. However, the biosynthesis of this moiety has remained elusive. Here, we show an oxidative enzyme-catalysed cascade that generates the THP ring of mupirocin. Rieske non-haem oxygenase (MupW)-catalysed selective oxidation of the C8–C16 single bond in a complex acyclic precursor is combined with an epoxide hydrolase (MupZ) to catalyse the subsequent regioselective ring formation to give the hydroxylated THP. In the absence of MupZ, a five-membered tetrahydrofuran ring is isolated, and model studies are consistent with cyclization occurring via an epoxide intermediate. High-resolution X-ray crystallographic studies, molecular modelling and mutagenesis experiments of MupZ provide insights into THP ring formation proceeding via an anti-Baldwin 6-endo-tet cyclization.

氧杂环，尤其是四氢吡喃（THP）和四氢呋喃，是许多具有生物活性的聚酮化合物天然产物的常见结构特征。莫匹罗星是从荧光假单胞菌中分离出的临床上重要的抗生素并组装在THP环上，这对生物活性至关重要。然而，该部分的生物合成仍然难以捉摸。在这里，我们显示了氧化酶催化的级联反应，产生了莫匹罗星的THP环。在复杂的无环前体中，Rieske非血红素加氧酶（MupW）催化的C8–C16单键的选择性氧化与环氧水解酶（MupZ）结合，以催化随后的区域选择性环形成，从而得到羟基化的THP。在没有MupZ的情况下，会分离出五元四氢呋喃环，并且模型研究与通过环氧化物中间体发生的环化反应是一致的。MupZ的高分辨率X射线晶体学研究，分子建模和诱变实验提供了通过反Baldwin 6- endo进行THP环形成过程的见解-tet环化。