Unlocking a Peroxidation Activity of Ketosteroid Isomerase with Ferrocenes as an Electron Mediator

Abstract

Enzymatic direct hydroxylation of steroid skeletons is vital for generation of physiologically and pharmacologically valuable compounds due to their structural and functional diversity. In this study, we discovered that ketosteroid isomerase (KSI) exhibited peroxidation activity using ferrocene and its analogues as electron mediators. KSI effectively converted steroidal and bicyclic enone substrates into hydroxylation products with 20–65% isolated yields in the presence of PPh3, providing an alternative approach to hydroxylation at the allyl position of steroidal and bicyclic enones. The mechanism studies suggested that the ferrocenium cation and radical intermediate were generated via a single-electron transfer process, and a reaction mechanism was proposed. This study not only demonstrates the catalytic diversity of KSIs via ferrocene-mediated electron transfer but also showcases valuable catalytic promiscuity of ketosteroid isomerases for design of enzymatic reactions and development of synthetic methods.