Plant-like cadinane sesquiterpenes from an actinobacterial mangrove endophyte

Cadinanes are typical plant sesquiterpenes with a broad range of biological functions. We report the isolation of three cadinanes (1-3) from a bacterial endophyte (Streptomyces sp.) of the mangrove plant Bruguiera gymnorrhiza. The structures of two new cadinenes, (+)-11-hydroxy-epicubenol (1) and (+)-12-hydroxy-epicubenol (2) were elucidated by nuclear magnetic resonance (NMR) and mass spectrometry. The bacterial product (+)-11-hydroxy-epicubenol was elucidated to be an enantiomer of the plant product pubinernoid C. (+)-12-Hydroxy-epicubenol was established as a diastereomer of the basidiomycete product trichapargin A. In addition, a crystal structure analysis corroborated the structure and configuration of 5,11-epoxy-10-cadinanol (3), a cadinane cycloether initially described as a natural product from liverwort. The discovery of oxygenated cadinanes from a bacterial endophyte may set the basis for the production of cadinanes by bacterial fermentation.

Keywords: 2D NMR; NMR; Streptomyces; cadinane; endophyte; epicubenol; sesquiterpene; terpene.