Biocatalytic Steroidal 9α‐Hydroxylation and Fragmentation Enable the Concise Chemoenzymatic Synthesis of 9,10‐Secosteroids

9,10‐Secosteroids are an important group of marine steroids with diverse biological activities. Herein, we report a chemoenzymatic strategy for the concise, modular, and scalable synthesis of ten naturally occurring 9,10‐secosteroids from readily available steroids in three to eight steps. The key feature lies in utilizing a Rieske oxygenase‐like 3‐ketosteroid 9α‐hydroxylase (KSH) as the biocatalyst to achieve efficient C9–C10 bond cleavage and A‐ring aromatization of tetracyclic steroids through 9α‐hydroxylation and fragmentation. With synthesized 9,10‐secosteroides, structure‐activity relationship was evaluated based on bioassays in terms of previously unexplored anti‐infective activity. This study provides experimental evidence to support the hypothesis that the biosynthetic pathway through which 9,10‐secosteroids are formed in nature shares a similar reaction cascade. In addition to the development of a biomimetic approach for 9,10‐secosteroid synthesis, this study highlights the great potential of chemoenzymatic strategies in chemical synthesis.