Biocatalysis of Cycloastragenol by Filamentous Fungi to Produce Unexpected Triterpenes

Abstract

AbstractThe biocatalysis of cycloastragenol, a natural tetracyclic triterpenoid with anti‐aging activity, by cultured whole cells of three strains of filamentous fungi, namely Cunninghamella elegans AS 3.1207, Syncephalastrum racemosum AS 3.264 and Doratomyces stemonitis AS 3.1411 produced 15 metabolites. Thirteen of them are new compounds. The structures of these metabolites were fully characterized on the basis of HR‐ESI‐MS analyses together with 1D and 2D NMR spectroscopy. The three fungal strains exhibited significant biocatalytic preferences: C. elegans enabled hydroxylation reactions, particularly on the 28‐ and 29‐CH3 groups; S. racemosum efficiently catalyzed a complicated rearrangement reaction to form the unusual ranunculane skeleton, which was further substituted with diverse side chains at C‐19; D. stemonitis mainly led to carbonylation reactions, especially on 3‐OH. It is particularly noteworthy that S. racemosum also catalyzed an unexpected ring expansion reaction to generate the rare 9(10)a‐homo‐19‐nor‐cycloartane skeleton. Biocatalysis was proved powerful in the structural diversification of cycloastragenol for future structure‐activity relationship studies.